QUAD [1] Original booklet reproduced at Jute on Amps [Archive]

Phil Allison[_3_]

June 14th 11, 06:37 AM

"Phil Allison"
>
>> Meanwhile, schematic here:
>>
>> http://ampslab.com/vintage_radford_sta100.htm
>
>
> ** Hmmmmm - two UL output stages powered from a common 600V DC supply
> with only simple cap filtering.
>
> With just 100uF effective capacitance, the peak to peak ripple at idle is
> about 18 volts or 3 % of the 600 rail.
>
> That 18 volts of ripple will rise to 45 or more at full output, or about
> 8%.
>
> Good balance in the output valves will prevent any audible hum, but has no
> effect on the 100 /120 Hz amplitude modulation the constantly varying
> screen supply voltage causes.
>
> Means there is a heck of a lot of work for the NFB loop to do.
>
> A filter choke in the PSU and two more caps would fix it completely.
>
> Was Arthur Radford a " penny pincher " ???
>
> Hmmmmmm........

** I little bit of searching finds that the STA100 was a PA amplifier built
to a strict budget.

http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg" It costs less than 10 shillings per watt " !!!!!Only 90 odd pounds for a 200 watt valve amp was a ** snip ** in 1967.Bet you will still find the odd one in some auditorium hooked up to a pair acolumn speakers with 12 inch Celestions and high frequency horns.Late 1967 was right at the end of the valve era for such amplifiers - cosin 1970 this beast appeared and changed the whole landscape.http://www.phaselinearhistory.stereomanuals.com/700seriesamp.htm.... Phil

Phil Allison[_3_]

June 14th 11, 06:59 AM

"Phil Allison"
>
>> Meanwhile, schematic here:
>>
>> http://ampslab.com/vintage_radford_sta100.htm
>
>
> ** Hmmmmm - two UL output stages powered from a common 600V DC supply
> with only simple cap filtering.
>
> With just 100uF effective capacitance, the peak to peak ripple at idle is
> about 18 volts or 3 % of the 600 rail.
>
> That 18 volts of ripple will rise to 45 or more at full output, or about
> 8%.
>
> Good balance in the output valves will prevent any audible hum, but has no
> effect on the 100 /120 Hz amplitude modulation the constantly varying
> screen supply voltage causes.
>
> Means there is a heck of a lot of work for the NFB loop to do.
>
> A filter choke in the PSU and two more caps would fix it completely.
>
> Was Arthur Radford a " penny pincher " ???
>
> Hmmmmmm........

** I little bit of searching finds that the STA100 was a PA amplifier built
to a strict budget.

<
http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg>

" It costs less than 10 shillings per watt " !!!!!

Only 90 odd pounds for a 200 watt valve amp was a ** snip ** in 1967.

Bet you will still find the odd one in some auditorium hooked up to a pair
of column speakers with 12 inch Celestions and high frequency horns !!!

Late 1967 was right at the end of the valve era for such amplifiers - cos
in 1970 this beast appeared and changed the whole landscape.

http://www.phaselinearhistory.stereomanuals.com/700seriesamp.htm

..... Phil

Patrick Turner

June 14th 11, 08:25 AM

On Jun 14, 11:57*am, "Phil Allison" > wrote:
> "Iain Churchus"
>
>
>
> > Enjoyed. Many thanks. I will try to reciprocate with
> > some docs on the Radford STA 100B (B=balanced input)
> > aother fine British valve/tube amp also used by the BBC.
>
> > Meanwhile, schematic here:
>
> >http://ampslab.com/vintage_radford_sta100.htm
>
> ** Hmmmmm *- *two UL output stages powered from a common 600V DC supply with
> only simple cap filtering.
>
> With just 100uF effective capacitance, the peak to peak ripple at idle is
> about 18 volts or 3 % of the 600 rail.
>
> That 18 volts of ripple will rise to 45 or more at full output, or about 8%.
>
> Good balance in the output valves will prevent any audible hum, but has no
> effect on the 100 /120 Hz amplitude modulation the constantly varying screen
> supply voltage causes.
>
> Means there is a heck of a lot of work for the NFB loop to do.
>
> A filter choke in the PSU and two more caps would fix it completely.
>
> Was Arthur Radford a " penny pincher " ???
>
> Hmmmmmm........
>
> .... *Phil

One of the reasons I have given for verifying my claim that the Quad-
II amp was under-designed, ie, designed with included shortcomings was
that Quad have a 16uF between OPT CT and 0V and the rectifier charges
to this point and there is about 22Vrms of ripple including lotsa
harmonics at this circuit point. Quad do have a 20H choke and
following 16uF to make a nice second order filter for the fixed KT66
screen supply and other HT uses including input stages and other
preamps and tuners used with Quad.

So when someone tries to use a 4 ohm speaker with a Quad-II strapped
for 8 ohms, then there is a small amount of class A PO and lotsa class
B where there is little inherent class A CMRR, so the CT hum becomes
in series with the Va on each wave half when each KT66 cuts off for
the majority of the wave.
This effect is reduced to a minima when the RL connected is 16 ohms
when the OPT is strapped for 8 ohms and the RLa-a then becomes about
8k2 including the OPT winding resistances, so all the action is pure
class A and THEN you'll get the quite decent THD/IMD/NOISE performance
from original Quad-II.

The Radford 100W amp may have have KT88 idling with total Pda at 50W
for both tubes. One might get 24W of class A, using a very much higher
RLa-a than the one which allows 100W of class AB1. The amount of pure
class A available for any PP tube amp = RLa-a/2 x Ia squared where Ia
is the idle Idc in one tube of the pair.
With Ea = 600V, and Ia at 41mA, Pda per tube at idle = 25W, and with
RLa-a = 4k8 you get a Va-a max of approx 707Vrms giving 104Watts on a
good day with following breeze. There is only 5 Watts of pure class A,
and yes, the NFB has some work to do as you correctly point out.

So, one would sensibly use the amp with RLa-a = 14 which gives 45W
AB1, and the first 12W is pure class A when the CMRR works fairly
well.

For only pure class A with the Radford 100W, you'd need RL a-a = 28k
ohms, but you only get about 23W max, but then it would be as clean as
a whistle, and the NFB would be very effective and DF excellent and
THD/IMD/Noise very low.

Old Raddy may have had a bean counting gene in his make up but so did
every other manufacturer.

Today, there is no need for plate chokes in amps like Quad-II or
Radford because one may use Si diodes plus large value electros. For
Radford, one might use Si diodes to charge two series 470uF uf caps
with a charge current limiting resistance in series with each pair of
2 x 1n5408 diodes in series off the HT winding with CT.
Then you'd need R = only 68 ohms plus a second pair 470uF caps, so
235u - 68r - 235u and if Idc = 0.16Adc then Vr at C2 = 0.15Vrms. A
choke of 4H would be better. Vr would then become 4mVrms, or SFA.
Resonance is at 5.2Hz. Not too bad.

ARC and Manley labs and others don't **** around with low values of
PSU capacitance. They just routinely use over 1,000uF between OPT CT
and 0V. The high value of C at CT means the CT is anchored to 0V via a
good low impedance value so IMD caused by LF modulating HF even in
class AB is minimised.

I use 470uF rated for 450V in Quad-II amps and they are FAR better
than the crap they had in 1950.

In Quad-II, the PSU noise may be about the same level as THD if one
measures these amps with an ideal load, and because good measurements
can be obtained, many will say there is no need to upgrade Quad-II,
but measurements can be misleading, and unlike Mr Walker, I design
with an open copy of RDH4 beside the bench and I try to make all my
new amps and re-engineered amps measure better than anything Walker
achieved.

Someone recently tried to shoot my arse off by saying 100,000 Quad-II
amps were made and they mostly have survived and there's no need to
alter anything. Well, due to OPT failures, I'd guess 20,000 Quad amps
were dumped, and replaced by SS stereo systems. 50,000 languish in
cupboards of old folks, and 30,000 are unaccounted for. Some might
even still get used sometimes, and not always into a 16 ohm load which
they rather like.

If I manage to seriously alter 20 pairs of Quad-II in a lifetime to
save folks from buying horrendously expensive new models of Quad amps,
then whose side am I on?

I am on the side of ordinary people and on the side of the music; I'm
trying to give both a fair go.

Patrick Turner.

Patrick Turner

June 14th 11, 08:35 AM

On Jun 14, 5:25*pm, Patrick Turner > wrote:
> On Jun 14, 11:57*am, "Phil Allison" > wrote:
>
>
>
>
>
> > "Iain Churchus"
>
> > > Enjoyed. Many thanks. I will try to reciprocate with
> > > some docs on the Radford STA 100B (B=balanced input)
> > > aother fine British valve/tube amp also used by the BBC.
>
> > > Meanwhile, schematic here:
>
> > >http://ampslab.com/vintage_radford_sta100.htm
>
> > ** Hmmmmm *- *two UL output stages powered from a common 600V DC supply with
> > only simple cap filtering.
>
> > With just 100uF effective capacitance, the peak to peak ripple at idle is
> > about 18 volts or 3 % of the 600 rail.
>
> > That 18 volts of ripple will rise to 45 or more at full output, or about 8%.
>
> > Good balance in the output valves will prevent any audible hum, but has no
> > effect on the 100 /120 Hz amplitude modulation the constantly varying screen
> > supply voltage causes.
>
> > Means there is a heck of a lot of work for the NFB loop to do.
>
> > A filter choke in the PSU and two more caps would fix it completely.
>
> > Was Arthur Radford a " penny pincher " ???
>
> > Hmmmmmm........
>
> > .... *Phil
>
> One of the reasons I have given for verifying my claim that the Quad-
> II amp was under-designed, ie, designed with included shortcomings was
> that Quad have a 16uF between OPT CT and 0V and the rectifier charges
> to this point and there is about 22Vrms of ripple including lotsa
> harmonics at this circuit point. Quad do have a 20H choke and
> following 16uF to make a nice second order filter for the fixed KT66
> screen supply and other HT uses including input stages and other
> preamps and tuners used with Quad.
>
> So when someone tries to use a 4 ohm speaker with a Quad-II strapped
> for 8 ohms, then there is a small amount of class A PO and lotsa class
> B where there is little inherent class A CMRR, so the CT hum becomes
> in series with the Va on each wave half when each KT66 cuts off for
> the majority of the wave.
> This effect is reduced to a minima when the RL connected is 16 ohms
> when the OPT is strapped for 8 ohms and the RLa-a then becomes about
> 8k2 including the OPT winding resistances, so all the action is pure
> class A and THEN you'll get the quite decent THD/IMD/NOISE performance
> from original Quad-II.
>
> The Radford 100W amp may have have KT88 idling with total Pda at 50W
> for both tubes. One might get 24W of class A, using a very much higher
> RLa-a than the one which allows 100W of class AB1. The amount of pure
> class A available for any PP tube amp = RLa-a/2 *x Ia squared where Ia
> is the idle Idc in one tube of the pair.
> With Ea = 600V, and Ia at 41mA, Pda per tube at idle = 25W, and with
> RLa-a = 4k8 you get a Va-a max of approx 707Vrms giving 104Watts on a
> good day with following breeze. There is only 5 Watts of pure class A,
> and yes, the NFB has some work to do as you correctly point out.
>
> So, one would sensibly use the amp with RLa-a = 14 which gives 45W
> AB1, and the first 12W is pure class A when the CMRR works fairly
> well.
>
> For only pure class A with the Radford 100W, you'd need RL a-a = 28k
> ohms, but you only get about 23W max, but then it would be as clean as
> a whistle, and the NFB would be very effective and DF excellent and
> THD/IMD/Noise very low.
>
> Old Raddy may have had a bean counting gene in his make up but so did
> every other manufacturer.
>
> Today, there is no need for plate chokes in amps like Quad-II or
> Radford because one may use Si diodes plus large value electros. For
> Radford, one might use Si diodes to charge two series 470uF uf caps
> with a charge current limiting resistance in series with each pair of
> 2 x 1n5408 diodes in series off the HT winding with CT.
> Then you'd need R = only 68 ohms plus a second pair 470uF caps, so
> 235u - 68r - 235u and if Idc = 0.16Adc then Vr at C2 = 0.15Vrms. A
> choke of 4H would be better. Vr would then become 4mVrms, or SFA.
> Resonance is at 5.2Hz. Not too bad.
>
> ARC and Manley labs and others don't **** around with low values of
> PSU capacitance. They just routinely use over 1,000uF between OPT CT
> and 0V. The high value of C at CT means the CT is anchored to 0V via a
> good low impedance value so IMD caused by LF modulating HF even in
> class AB is minimised.
>
> I use 470uF rated for 450V in Quad-II amps and they are FAR better
> than the crap they had in 1950.
>
> In Quad-II, the PSU noise may be about the same level as THD if one
> measures these amps with an ideal load, and because good measurements
> can be obtained, many will say there is no need to upgrade Quad-II,
> but measurements can be misleading, and unlike Mr Walker, I design
> with an open copy of RDH4 beside the bench and I try to make all my
> new amps and re-engineered amps measure better than anything Walker
> achieved.
>
> Someone recently tried to shoot my arse off by saying 100,000 Quad-II
> amps were made and they mostly have survived and there's no need to
> alter anything. Well, due to OPT failures, I'd guess 20,000 Quad amps
> were dumped, and replaced by SS stereo systems. 50,000 languish in
> cupboards of old folks, and 30,000 are unaccounted for. Some might
> even still get used sometimes, and not always into a 16 ohm load which
> they rather like.
>
> If I manage to seriously alter 20 pairs of Quad-II in a lifetime to
> save folks from buying horrendously expensive new models of Quad amps,
> then whose side am I on?
>
> I am on the side of ordinary people and on the side of the music; I'm
> trying to give both a fair go.
>
> Patrick Turner.- Hide quoted text -
>
> - Show quoted text -

Iain Churches[_2_]

June 14th 11, 09:17 AM

"Phil Allison" > wrote in message
...
>
> ** I little bit of searching finds that the STA100 was a PA amplifier
> built
> to a strict budget.
>
> <
> http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg>
>
> " It costs less than 10 shillings per watt " !!!!!
>
> Only 90 odd pounds for a 200 watt valve amp was a ** snip ** in 1967.

That was a month's salary for many people!

> Bet you will still find the odd one in some auditorium hooked up to a pair
> of column speakers with 12 inch Celestions and high frequency horns !!!
>

If you do, offer to exchange it for something "better and more modern"
The STA100 rarely seen for sale, and is highly sought after. A pristine
original example was recently sold for GBP 2000.

Cheers
Iain

Iain Churches[_2_]

June 14th 11, 09:20 AM

"Phil Allison" > wrote in message
...
>
> "Iain Churches"
>>
>> Enjoyed. Many thanks. I will try to reciprocate with
>> some docs on the Radford STA 100B (B=balanced input)
>> aother fine British valve/tube amp also used by the BBC.
>>
>> Meanwhile, schematic here:
>>
>> http://ampslab.com/vintage_radford_sta100.htm
>
>
> ** Hmmmmm - two UL output stages powered from a common 600V DC supply
> with only simple cap filtering.
>
> With just 100uF effective capacitance, the peak to peak ripple at idle is
> about 18 volts or 3 % of the 600 rail.

The electrolytics are mounted under the chassis and
physically very large indeed. They are marked 1000Vwkg
Perhaps in those days higher value caps at this working
voltage were not available, and that he was just using what
he could get ?

> Was Arthur Radford a " penny pincher " ???

Or perhaps Arthur Radford reasoned that
for a commercial amp, overkill just added to the cost

Driving at 1kHz at 100W, my STA 100B has THD 0.09%
Not too shabby, I am sure you will agree:-)

> That 18 volts of ripple will rise to 45 or more at full output, or about
> 8%.
>
> Good balance in the output valves will prevent any audible hum,

Yes. even with ETS (ear to speaker) there is no audible hum on
B+W Nautitlus 802.

> Means there is a heck of a lot of work for the NFB loop to do.

The STA100 has 20dB of NFB and is unconditionally stable.
The manual also states that it can run contiuously and at full
power into shorted or open loads. The expected life span of the
OP was given as 21 years continuous use. A BBC service
tech told me that he cannot recall a single Radford amplifier
that suffered component failure. The BBC had dozens of them.
Mine is a balanced line version ex-BBC.

The whole Radford story is an interesting one. Founded in 1945
the company was in fact a builder of electronics lab test instruments -
low distortion oscillators, psophometers etc, and only began to produce
audio amplifiers (the MA 12 and MA 15 where the first) some ten
years later when a British dealer took him a Dynaco to measure.
Radford is said to have remarked " I can make something far better
than this"

Both he, and his associate Dr A R Bailey, had close
connections with the studio at which I worked in the UK.
We used Radford STA25 amplifiers and Tannoy Lancasters
as the standard monitoring set up in probably thirty
rooms. The studio control rooms had STA 100s.

Wiki has some info at:

http://en.wikipedia.org/wiki/Radford_Electronics

Regards
Iain

Phil Allison[_3_]

June 14th 11, 11:21 AM

"Iain Churchus Retarded ****wit"

>> A little bit of searching finds that the STA100 was a PA amplifier
>> built to a strict budget.
>>
>> <
>> http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg>
>>
>> " It costs less than 10 shillings per watt " !!!!!
>>
>> Only 90 odd pounds for a 200 watt valve amp was a ** snip ** in 1967.
>
>
>> Bet you will still find the odd one in some auditorium hooked up to a
>> pair
>> of column speakers with 12 inch Celestions and high frequency horns !!!
>>
>
> If you do, offer to exchange it for something "better and more modern"
> The STA100 rarely seen for sale, and is highly sought after. A pristine
> original example was recently sold for GBP 2000.

** So do old coins and bits of furniture.

Read the ****ing blurb FROM RADFORD themselves !!!

You retarded MORON !!!!!!!!

The POS is a ****ing Public Address amp.

.... Phil

Patrick Turner

June 14th 11, 11:23 AM

On Jun 14, 6:17*pm, "Iain Churches" > wrote:
> "Phil Allison" > wrote in message
>
> ...
>
>
>
> > ** I little bit of searching finds that the STA100 was a PA amplifier
> > built
> > to a strict budget.
>
> > <
> >http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford...>
>
> > " It costs less than 10 shillings per watt " *!!!!!
>
> > Only 90 odd pounds for a 200 watt valve amp was a ** snip ** *in 1967..
>
> That was a month's salary for many people!

How many ppl exactly?

90 british pounds in 1967 might have been $180 in Oz and AWE for 1967
was $62.
So, the amp cost 3 week's AWE. In today's figures where AWE = $865,
the cost would be about $2,600, and I assume $5,200 for two channels.
Quad-II Forty in Oz are similarly priced but there is -8dB less power
per amplifier.
>
> > Bet you will still find the odd one in some auditorium hooked up to a pair
> > of column speakers with 12 inch Celestions and high frequency horns !!!
>
> If you do, offer to exchange it for something "better and more modern"
> The STA100 rarely seen for sale, and is highly sought after. *A pristine
> original example was recently sold for GBP 2000.

So what. Pristine Quad-II might sell for $3,000, not worth it really.
I've seen a Klangfilm theatre amp system with preamp go for $7,000.
Much repair work had been done, not at all mint. Has 6 x EL34 with Ea
at 900Vdc. Goord, I cooda easy made better. It seems to me the mantra
of "Thou Shalt Honour Thy Brand Name" is alive and well, and the past
sells for silly prices to be company during someone's probable short
future, ie, some rich old ******* gets something to cling to before
the coffin lid is screwed down.

Patrick Turner.
>
> Cheers
> Iain

Phil Allison[_3_]

June 14th 11, 11:27 AM

"Iain Churchus is full of **** "

> The electrolytics are mounted under the chassis and
> physically very large indeed.

** So ****ing what ?

They are far to small in VALUE !!!!!!!!!!!!!!!

> Driving at 1kHz at 100W, my STA 100B has THD 0.09%
> Not too shabby, I am sure you will agree:-)

** Not even faintly possible with the schem as published.

The modulation hum would exceed 1 %.

>> That 18 volts of ripple will rise to 45 or more at full output, or about
>> 8%.
>>
>> Good balance in the output valves will prevent any audible hum,
>
> Yes. even with ETS (ear to speaker) there is no audible hum on
> B+W Nautitlus 802.
>
>> Means there is a heck of a lot of work for the NFB loop to do.
>
>
> The STA100 has 20dB of NFB and is unconditionally stable.

** So ****ing what ?

> The manual also states that it can run contiuously and at full
> power into shorted or open loads.

** Absolute bull****.

The STA100 is a cut to the bone, PA amplifier.

Sold dirt cheap, maybe below cost of production in late 1967.

Just to get rid of them.

BTW

FFS learn to spell "continuously".

..... Phil

Phil Allison[_3_]

June 14th 11, 11:31 AM

" Iain Churchus is a ****** "

> The electrolytics are mounted under the chassis and
> physically very large indeed. They are marked 1000Vwkg

** So you say Radford put two * rare as hens teeth * 1000V electros in
SERIES on a 600V rail ??

Pic required.

This is too funny for words.

..... Phil

Patrick Turner

June 14th 11, 11:48 AM

?
>
> > Was Arthur Radford a " penny pincher " ???
>
> Or perhaps Arthur Radford reasoned that
> for a commercial amp, overkill just added to the cost

What a frightful attitude!
>
> Driving at 1kHz at 100W, my STA 100B has THD 0.09%
> Not too shabby, I am sure you will agree:-)

This is very hard to believe, considering most of the power is in
class B and that typical THD with no GNFB is 6%+ for UL amps like this
one. With 20dB GNFB you'd reduced THD to maybe 0.6%. I might believe
0.09% THD at 10 watts, but not at 100W.

> The STA100 has 20dB of NFB and is unconditionally stable.
> The manual also states that it can run contiuously and at full
> power into shorted or open loads. *

Very silly talk indeed. at full power? There is no power produced with
a short circuit load or an open circuit.

However, with a shorted output, and with the same input signal used
for 100W at 1khz into the rated load for 100W, the amp would have no
NFB so the **current** waves at the output will be square waves, and
the OP stage will be very over driven with coupling caps charged up
with DC so that OP tubes are effectively biased to operate in class C
as switches, so average current x average voltage may not exceed Pda
of 42 watts for the tubes.

But I bet I could make a Radford melt its tubes like what happens in
so many peculiar situations which I end up having to repair.

> OP was given as 21 years continuous use. *

Is that all? I've seen many hot running PTs in old junk run for 70
years OK.

> A *BBC service
> tech told me that he cannot recall a single Radford amplifier
> that suffered component failure.

That's like saying not one British Centurion tank ever broke down, or
that not one Rolls Royce break down.
I reckon the BBC service guy had dementia.

> The BBC had dozens of them.
> Mine is a balanced line version ex-BBC.

Regardless of my criticisms, Radford tube amps were not too bad but
who'd want 100W of mainly class AB power when you could have 6 x 6L6GC
with Ea at a comfortable 420 V and get a whole lot more class A %?

> The whole Radford story is an interesting one. *Founded in 1945
> the company was in fact a builder of electronics lab test instruments -
> low distortion oscillators, psophometers etc, and only began to produce
> audio amplifiers (the MA 12 and MA 15 where the first) some ten
> years later when a British dealer took him a Dynaco to measure.
> Radford is said to have remarked " I can make something far better
> than this"

I can understand that very easily.

>
> Both he, and his associate Dr A R Bailey, had close
> connections *with the studio at which I worked in the UK.
> We used Radford STA25 amplifiers and Tannoy Lancasters
> as the standard monitoring set up in probably thirty
> rooms. The studio control rooms had STA 100s.

Maybe most power levels were quite low in the Tannoys. Tannoys have
sensitivity of 95dB/W/M, no?
Maybe average levels were only 0.5W per channel.
Hence good sound.

Patrick Turner.

Patrick Turner

June 14th 11, 12:08 PM

On Jun 14, 8:31*pm, "Phil Allison" > wrote:
> " Iain Churchus is a ****** "
>
> > The electrolytics are mounted under the chassis and
> > physically very large indeed. *They are marked 1000Vwkg
>
> ** So you say Radford put two ** rare as hens teeth * *1000V electros in
> SERIES *on a *600V rail ??
>
> Pic required.
>
> This is too funny for words.
>
> .... *Phil

There are a number of nostalgically minded gentlemen whose rose
coloured memories of the wonderful good old days continue to to expand
in their minds. It is a very benign behavioural trait among many older
blokes, but although I am an older bloke no such phenomena can be
found between my ears and I much prefer the cold hard realities about
everything anywhere and all times and forever. It surely grates on
many ppl but I spend a lotta time being happy.

I kept a diary from my early years which lists the pains and aches of
living I encountered while experiencing the 1960s, and it lists the
constant stream of lies I was told by advertising companies,
governments, and military spokesmen and girlfriends. From an early
time I wanted evidence to back all claims. All claims were false
unless proven otherwise. The belief in Santa didn't last long. At 16 I
figured the Catholic Church would flourish without me, and at 18 I
reckoned the Vietnamese could sort out their own bothers and didn't
need my assistance.

So when anyone exagerated amplifier capabilities, I wouldn't believe
them either, and Radford and Quad could definately rely on me to never
buy their products. I saw plenty of fellas make their own amps which
performed as well or better than best brandnames. Someone said drink
Coca Cola. I still don't.

Patrick Turner.

Iain Churches[_2_]

June 14th 11, 12:34 PM

"Patrick Turner" > wrote in message
...
?
>
> > Was Arthur Radford a " penny pincher " ???
>
>> Or perhaps Arthur Radford reasoned that
>> for a commercial amp, overkill just added to the cost

>What a frightful attitude!

Who knows?

> Driving at 1kHz at 100W, my STA 100B has THD 0.09%
> Not too shabby, I am sure you will agree:-)

>This is very hard to believe, considering most of the power is in
>class B and that typical THD with no GNFB is 6%+ for UL amps like this
>one. With 20dB GNFB you'd reduced THD to maybe 0.6%. I might believe
>0.09% THD at 10 watts, but not at 100W.

All Radford amplifiers, the STA 15, STA 25 and STA 100
had a published distortion fig of 0.1% at rated power output.

> The STA100 has 20dB of NFB and is unconditionally stable.
> The manual also states that it can run continuously and at full
> power into shorted or open loads.

>Very silly talk indeed. at full power? There is no power produced with
>a short circuit load or an open circuit.

Probably means when driven with a signal that would produce
full power when working into a load. I have the documentation
filed away somewhwere. I will make a pdf.

> OP was given as 21 years continuous use.

>Is that all? I've seen many hot running PTs in old junk run for 70
>years OK.

Note: "continuous"

>> Both he, and his associate Dr A R Bailey, had close
>> connections with the studio at which I worked in the UK.
>> We used Radford STA25 amplifiers and Tannoy Lancasters
>> as the standard monitoring set up in probably thirty
>> rooms. The studio control rooms had STA 100s.

>Maybe most power levels were quite low in the Tannoys. Tannoys have
>sensitivity of 95dB/W/M, no?
>Maybe average levels were only 0.5W per channel.
>Hence good sound.

In those days, before Tannoy had a professional
division, many UK studios also used Lockwood speakers,
with Tannoy Gold 15" monitors. I doubt that Gary Glitter
was mixed at 0.5W per channel :-)

The BBC had a monitor speaker built by Kef, (impedance
25 Ohms) that had a special 25 Ohm Radford amp built in
on a shelf at the bottom.

Besides being a designer of test equipment and audio
amplifiers, Arthur Radford, together with Dr Arthur Bailey
also did pioneering work on the acoustic transmission line
loudspeaker, and published an article in Wireless Word.

http://en.wikipedia.org/wiki/Acoustic_transmission_line

Iain

John Byrns

June 14th 11, 03:33 PM

In article >,
"Phil Allison" > wrote:

> "Iain Churchus is full of **** "
>
>
> > The electrolytics are mounted under the chassis and
> > physically very large indeed.
>
>
> ** So ****ing what ?
>
> They are far to small in VALUE !!!!!!!!!!!!!!!
>
>
> > Driving at 1kHz at 100W, my STA 100B has THD 0.09%
> > Not too shabby, I am sure you will agree:-)
>
>
> ** Not even faintly possible with the schem as published.
>
> The modulation hum would exceed 1 %.

You could both be correct, depending on the methods you are using to measure the
"THD". Some "THD" measuring instruments don't resolve the modulation sidebands
around the fundamental as distortion.

So the question becomes what sort of "THD" measuring kit was Iain using?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

Phil Allison[_3_]

June 14th 11, 03:41 PM

"John Byrns"
>
> You could both be correct, depending on the methods you are using to
> measure the
> "THD". Some "THD" measuring instruments don't resolve the modulation
> sidebands
> around the fundamental as distortion.

** FFS - cite what famous brand test gear does that.

Alluding to your own alleged, secret knowledge helps no-one.

> So the question becomes what sort of "THD" measuring kit was Iain using?

** Iain has no ****ing idea how to use audio test equipment and is ALWAYS
reckless in the extreme with facts.

No ** one single thing** he posts is EVER to be believed.

..... Phil

John Byrns

June 14th 11, 04:10 PM

In article >,
"Phil Allison" > wrote:

> "John Byrns"
> >
> > You could both be correct, depending on the methods you are using to
> > measure the
> > "THD". Some "THD" measuring instruments don't resolve the modulation
> > sidebands
> > around the fundamental as distortion.
>
> ** FFS - cite what famous brand test gear does that.
>
> Alluding to your own alleged, secret knowledge helps no-one.

I have no "secret knowledge" in this area, I am referring to any of the many THD
measuring sets that used a notch filter to remove the fundamental, and many of
the distortion products below the second harmonic, displaying what remained on a
meter as a measure of the distortion. Terminals were also often provided to
display the residual out of the notch filter on a CRO.

If you can't identify any "famous brand test gear" that used this technique,
then you are completely hopeless.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

Patrick Turner

June 15th 11, 12:27 AM

On Jun 15, 1:10*am, John Byrns > wrote:
> In article >,
> *"Phil Allison" > wrote:
>
> > "John Byrns"
>
> > > You could both be correct, depending on the methods you are using to
> > > measure the
> > > "THD". *Some "THD" measuring instruments don't resolve the modulation
> > > sidebands
> > > around the fundamental as distortion.
>
> > ** *FFS * - *cite what famous brand test gear does that.
>
> > *Alluding to your own alleged, secret knowledge helps no-one.
>
> I have no "secret knowledge" in this area, I am referring to any of the many THD
> measuring sets that used a notch filter to remove the fundamental, and many of
> the distortion products below the second harmonic, displaying what remained on a
> meter as a measure of the distortion. *Terminals were also often provided to
> display the residual out of the notch filter on a CRO.
>
> If you can't identify any "famous brand test gear" that used this technique,
> then you are completely hopeless.
>
> --
> Regards,
>
> John Byrns
>
> Surf my web pages at, *http://fmamradios.com/

I have measured a very large number of amplifiers for THD production
using a 1kHz test signal which has 0.003% THD or less. The notch
filter I use leaves ALL other artifacts other than the 1 kHz test
tone. Usually tube amps never measure with less than 0.003% THD and if
they do then usually the noise swamps the measurements. 0.003% is -
90dB. I do have a switchable HP filter to remove LF noise which may
be at a level which is higher than the harmonics of 1 kHz. there are
usually very low "modulation sidebands around the fundamental as
distortion" when a tube amp is tested at low level. In tube amplifiers
with very poor filtering of the B+ anode supply such as Quad-II,
Radford and many others, at the higher levels there is some amplitude
modulation by the hum frequency and you find the 2H, 3H and 5H has an
envelope shape indicating the presence of sum and difference harmonic
products, say 3,100Hz and 2,900 Hz. The amount of such harmonics
rapidly increases during the B part of AB operation, and many
manufacturers didn't give a **** about Intermodulation products formed
between 1 kHz test tones and PSU rails because the measured increase
in THD due to non smooth PSU rails is so small.

In Quad-II, one is very lucky to ever see 0.1% THD at 20Watts. Usually
its 0.25% and sometimes 2.5% if the tubes have become old and fairly
unmatched and the balance of AC drive to OP tubes has become quite
poor. In fact most old Quad-II amps never get near the original specs.
And perhaps 1/2 the amount of harmonic grunge measured is PSU caused
IMD. Walker tested brand new amps with all the R&C values as they
should be and with mew tubes and he didn't worry that IMD from PSU =
THD roughly - the measurement was a low figure, maybe 0.02% at 2
watts, ie, - 74dB, and who ever could hear any of that? The distortion
of his amps in 1955 was probably at least an order of magnitude less
than many signal sources at the time.

Measurements of tube amps may be somewhat poor but they often sound
"better" than solid state amps which sometimes measure 100 times
better, ie instead of 0.1% at 20W, you get 0.001%. I find that where
one does achieve 0.1% THD at 20W with a tube amp AND where completely
negligible PSU IMD products and harmonics are present then music
sounds well.

IMD testing as mentioned in RDH4 is where you have 4Vrms of say 75Hz
and 1Vrms of 5 kHz present in an output signal and you measure the
envelope % modulation of the 5kHz, or else measure levels of side
bands each side of 5kHz, ie, 4,925Hz and 5,075Hz. One may find the IMD
products formed by presence of high level lower frequencies completely
swamp the effects of the Vripple on a supply rail.
All such IMD is lessened by use of high value caps between the CT and
0V rails.

Music contains a myriad of frequencies being present simultaneously
and there is a very complex range of IMD products formed by amplifiers
which if separated from the pure music input signal would sound like
scratchy pink noise rising and falling in time with the music levels
and complexity. Its utter mud. Its the veil they talk about. Its far
more important to have low IMD than have low THD because nearly all
music tones have many harmonics, and if each His altered +/- 5% nobody
will notice. But if some other horrid an-harmonic tone is added by
electronics then we all notice.

Patrick Turner.

John L Stewart

June 15th 11, 02:04 AM

Iain Churches[_2_]

June 15th 11, 09:55 AM

"John Byrns" > wrote in message
...
> In article >,
> "Phil Allison" > wrote:
>
>> > The electrolytics are mounted under the chassis and
>> > physically very large indeed.
>>
>>
>> They are far to small in VALUE !!!!!!!!!!!!!!!
>>
>>
>> > Driving at 1kHz at 100W, my STA 100B has THD 0.09%
>> > Not too shabby, I am sure you will agree:-)
>>
>>
>> ** Not even faintly possible with the schem as published.

LOL :-)

I thought it was only Stuart Pinkerton who could write
a technical review of an amplifier by looking at the schematic.

Besides, don't you think that Radford's major customers,
the BBC, and UK recording studios would have questioned
his published spec if it was incorrect?

>>
>> The modulation hum would exceed 1 %.
>
> You could both be correct, depending on the methods you are using to
> measure the
> "THD". Some "THD" measuring instruments don't resolve the modulation
> sidebands
> around the fundamental as distortion.
>
> So the question becomes what sort of "THD" measuring kit was Iain using?

Hello John,

I have two distortion analysers, HP 332A and Ferrograph RTS.
This amp was also loaned to a colleague of mine at Scandi
Broadscasting who wanted to hear it driving some large
B+ W speakers. He measured its bandwidth and THD on a
KH analyser and gave me the fig of 0.09% which I quoted above.
The amplifier's printed specification is 0.1%

Regards
Iain

Iain Churches[_2_]

June 15th 11, 09:56 AM

"Patrick Turner" > wrote in message
...
?

Iain wrote
>> A BBC service
>> tech told me that he cannot recall a single Radford amplifier
>> that suffered component failure.

>That's like saying not one British Centurion tank ever broke down, or
>that not one Rolls Royce break down.

Is it?

> I reckon the BBC service guy had dementia.

In broadcasting and studios the standard way to avoid
breakdowns is to schedule more-frequent regular
preventitve maintenance and replace components long before
the change is due, so that the chance of failure is much reduced,
and equipment never needs to send out smoke signals.

Iain

Phil Allison[_3_]

June 15th 11, 11:00 AM

"Iain Churchus = ****ING LIAR "
>
>>> They are far to small in VALUE !!!!!!!!!!!!!!!
>>>
>>>
>>> > Driving at 1kHz at 100W, my STA 100B has THD 0.09%
>>> > Not too shabby, I am sure you will agree:-)
>>>
>>>
>>> ** Not even faintly possible with the schem as published.

>
> Besides, don't you think that Radford's major customers,
> the BBC, and UK recording studios would have questioned
> his published spec if it was incorrect?

** What specs ?????

You have not supplied a copy of any specs.

Radford described the POS as a public address amplifier and sold it at a
fire sale price in late 1967.

Cos it was a useless, out of date, ****ing POS.

http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg

100 volt line output ??

Under 10 shillings a watt in 1968 ??

Piece of ****.

..... Phil

Iain Churches[_2_]

June 15th 11, 01:03 PM

"Phil Allison" > wrote in message
...
>

>>>> They are far to small in VALUE !!!!!!!!!!!!!!!
>>>>
>>>>
>>>> > Driving at 1kHz at 100W, my STA 100B has THD 0.09%
>>>> > Not too shabby, I am sure you will agree:-)
>>>>
>>>>
>>>> ** Not even faintly possible with the schem as published.
>
>>
>> Besides, don't you think that Radford's major customers,
>> the BBC, and UK recording studios would have questioned
>> his published spec if it was incorrect?
>
> ** What specs ?????
>
> You have not supplied a copy of any specs.

Plenty of documentation available.

Why do you think I would take the trouble to
look for and copy a spec sheet for an ill-mannered
person like yourself with the social graces of a raccoon,
and with whom rational informative discussion is impossible?

>
> Radford described the POS as a public address amplifier and sold it at a
> fire sale price in late 1967.
>
> Cos it was a useless, out of date, ****ing POS.

It was a standard monitor amp at the BBC and in many of
the major recording studios. Decca, where I worked had a
large number of them.

>
> http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg
>
> 100 volt line output ??

100V line was an option. Leak offered it too, but that does not
turn either the Radford or the Leak into a PA amplifier.

All broadcast and studio versions (model B) had balanced
line inputs on XLR and a 16/8 Ohm OPT, as per the schematic
to which I posted a link. BTW did that schematic have a
100V line output? Of course not!

The amps that were paired with the Radford/Kef BBC
monitor loudspeakers had a single secondary OPT winding
of 25 Ohms to match the speaker.

>
> Under 10 shillings a watt in 1968 ??

I doubt that many were made for factory or PA use.
That was not Radford's market. Tannoy and British
Vortexion had the major slice of that sector. Once
again, if you choose to do some careful reading,
in place of your cut and paste expletives you will
find that what I have told you is fact.

Iain

Patrick Turner

June 15th 11, 04:03 PM

On Jun 15, 6:56*pm, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
> ?
>
> Iain wrote
>
> >> A BBC service
> >> tech told me that he cannot recall a single Radford amplifier
> >> that suffered component failure.
> >That's like saying not one British Centurion tank ever broke down, or
> >that not one Rolls Royce break down.
>
> Is it?
>
> > I reckon the BBC service guy had dementia.
>
> In broadcasting and studios the standard way to avoid
> breakdowns is to schedule more-frequent regular
> preventitve maintenance and replace components long before
> the change is due, so that the chance of failure is much reduced,
> and equipment never needs to send out smoke signals.
>
> Iain

Well, perhaps the BBC spent more on maintenance than other
institutions or companies. But ordinary consumers rarely ever service
gear preventively, so the clouds of smoke bring them in droves to me
because **** happens. But its not just old amps that fail. Companies
have techs to design gear using PC aided design programs and all is
simulated then manufactured without extensive tests in HOT ROOMS to
see what fails when things get hot. Nup, the consumer gets to be the
test guy these days. So I get stuff than went BANG at the first time
it was turned on, ****ed PT and CD player, totally inadequate
protection. One Emotiva amp destroyed one of its 5 x 200W channels
last week. No reason, just a bang, smoke, and silence. Filthy
complexity on the boards. Emotiva send a new amp module with board and
HS for free, and don't want the old one returned. This Chinese amp is
made so cheaply that accepting returns costs more than their
manufacture, so they charge a big price online, and they don't mind if
10% fail, they are way in front at the bank.

The trouble is that nobody can pass laws requiring gear failure rates
to be under 1% over 5 years. Ah, the wonderful efforts of the Whatever
Generation!

Patrick Turner.

John L Stewart

June 16th 11, 01:35 AM

Hello John,

I have two distortion analysers, HP 332A and Ferrograph RTS.
This amp was also loaned to a colleague of mine at Scandi
Broadscasting who wanted to hear it driving some large
B+ W speakers. He measured its bandwidth and THD on a
KH analyser and gave me the fig of 0.09% which I quoted above.
The amplifier's printed specification is 0.1%

Regards
Iain[/QUOTE]

Hi Iain- My THD paralyzer is an HP 334A, very nice indeed. Was US Government stuff. Still has the USAF cal sticker, new straight out of the box when I bought it as surplus. Not familiar with the Ferrograph at all, perhaps they are not sold in Canada.

Also built a vacuum tube wein bridge version many years ago. Its been on the shelf a long time.

Also have four of the Pico Technology FFT's up to 250 MHz. The most useful for what I do is their 3224, a 12 bit, 10 MHz box. Also have their ADC-216, a 16 bit box primarily for audio. I used it a lot while putting together several of the audio amp projects I did for publishing a few years ago. Does a great job looking for PS related IM products.

Retired again from hitech sales at 78 but now the focus is on getting our acres in order. Lots of manual labor & otherwise the bicycle has priority!

Cheers, John

PS- I worked on that DeHavilland Vampire issuing the tongue of fire many years ago. Had a camera on hand & got a great shot.

Iain Churches[_2_]

June 16th 11, 07:29 AM

"flipper" > wrote in message
...

> I don't have an opinion on the Radford but to say they simply
> described it as a public address amplifier is a misrepresentation as
> they explicitly claim a few sentences on down that it's 'performance'
> is equal to the 'best' low power high fidelity amplifier.

Of course it is not a PA amp, Flipper, although some may
have been sold for that application.

The STA100 was designed because studios and
broadcast in the UK had stated that both the
Radford STA25 and the Quad were
underpowered for their needs.

I have an original Radford booklet somewhere,
but in the meantime, here is the entry from a UK
Broadcast Yearbook 1969:

Radford STA100.
Stereo Valve amplifier. Output 100W RMS per channel.
THD Less than 0.1% at 1kHz rated output.
FR 20Hz - 20kz -1dB +0dB.
Noise level -95dB at 60W
Input 350mV
Output valves KT88
Mains powered. Price £112.10

I would add that when measured the power
bandwidth (-3dB points at full power) were
8Hz - 58kHz.

In the UK in 1968, UKP112 was quite a lot
of money. According to a table published by
the Financial Times, the average salary (gross)
was UKP 1,488.98 so UKP28 per week.
Thus the STA was about a month's salary
(gross) for most of us.

Just as a comparison, the average salary in
the UK in 2010 was UKP 39,000 which is
750 per week. This would put the STA100
in today's money at: UKP 3000 that's USD 4250.
or AUD 4020. Cheap? I don't think so!

Regards
Iain

Iain Churches[_2_]

June 16th 11, 07:31 AM

"Patrick Turner" > wrote in message
...
On Jun 15, 6:56 pm, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
> ?
>
> Iain wrote
>
> >> A BBC service
> >> tech told me that he cannot recall a single Radford amplifier
> >> that suffered component failure.
> >That's like saying not one British Centurion tank ever broke down, or
> >that not one Rolls Royce break down.
>
> Is it?
>
> > I reckon the BBC service guy had dementia.
>
> In broadcasting and studios the standard way to avoid
> breakdowns is to schedule more-frequent regular
> preventitve maintenance and replace components long before
> the change is due, so that the chance of failure is much reduced,
> and equipment never needs to send out smoke signals.

>Well, perhaps the BBC spent more on maintenance than other
>institutions or companies.

I think that most broadcasters and professsional studios
adopted similar strategies. In the studio complex where
I worked, each piece of equipment had its own log book
with a routine service schedule. Analogue tape machines
for example were high maintenance. The electronics were
set up daily by the studio assistants. First, heads were
cleaned and demagged. Then, and only then the replay
chain was aligned to a standard reference tape. In control
rooms with large format multitrack recorders, all with
Dolby A processors this took some time. But it was still a
part of the daily routine, and ensured compatability from
location to location.

Any potential faults were noted in the service log, which
was checked by the service personnel on a daily basis.
Tape machines were replaced by another of the same make
and model temporarily during service. Pieces of equipment
that might have been prone to failure such as valve amplifiers
received regular preventitve maintenance.

Faults such as an OC bias pot were potentially fatal.
These WW pots were changed regularly. Valves too
were tested and changed long before they had reached
the end of their working life. But this means
major breakdowns and disasters were avoided.

In these digital days, equipment is potentially more
reliable. I knew of a graphics post production that
had a Quantel workstation with thirty hard disks, all
hand picked for Quantel by Fujitsu. These were
changed regularly, and those taken out of service send
back for refurbishment under an exchange contract.

>But ordinary consumers rarely ever service
>gear preventively, so the clouds of smoke bring them in droves to me
>because **** happens.

Yes indeed:-) There is a very nice fellow in Stockholm, who,
up until his recent retirement was a bespoke valve/tube amp
builder, just like yourself. His amplifiers were had crafted and
very expensive. He offered a ten year guarantee (original owner).
But there was much small print. The amplifier had to be returned
(freight at the owner's expense) for service, checking and maintenance
at regular intervals. Valves, power resistors, pots etc were changed
long before they had reached the end of their active life. Most of his
clients were local, and he would provide a replacement amp if required
while their own was being serviced.

>But its not just old amps that fail. Companies
>have techs to design gear using PC aided design programs and all is
>simulated then manufactured without extensive tests in HOT ROOMS to
>see what fails when things get hot. Nup, the consumer gets to be the
>test guy these days. So I get stuff than went BANG at the first time
>it was turned on, ****ed PT and CD player, totally inadequate
>protection. One Emotiva amp destroyed one of its 5 x 200W channels
>last week. No reason, just a bang, smoke, and silence. Filthy
>complexity on the boards. Emotiva send a new amp module with board and
>HS for free, and don't want the old one returned. This Chinese amp is
>made so cheaply that accepting returns costs more than their
>manufacture, so they charge a big price online, and they don't mind if
>10% fail, they are way in front at the bank.

Yes. I have always wondered what happened in the case of a
Chinese amp that exhibited pyrotechnics, as most of them are
bought direct, and not through a local dealer who would normally be
responsible for warranty repairs.

> The trouble is that nobody can pass laws requiring gear failure rates
> to be under 1% over 5 years. Ah, the wonderful efforts of the Whatever
> Generation!

In broadcast and studios, bad news travels fast. So manufacturers
do their best to keep the clients happy. That's the only was to get
repeat high volume orders.

Iain

Patrick Turner

June 16th 11, 09:34 AM

>
I've never worked for BBC, or Austraya's ABC or the private broadcast
or show production networks or companies. Things do go astray in Oz,
despite service staff, and for example, silence in the middle of radio
programme is all too common. What goes in in the background, such as
false service reports, "yes we checked" it says on the bit of paper or
computer record, but no, just not done. Humans meant to check things
seldom ever check as much as they should check. They look, unit on, no
smoke, she'll be right.

> >But ordinary consumers rarely ever service
> >gear preventively, so the clouds of smoke bring them in droves to me
> >because **** happens.
>
> Yes indeed:-) * There is a very nice fellow in Stockholm, who,
> up until his recent retirement was a bespoke valve/tube amp
> builder, just like yourself. His amplifiers were had crafted and
> very expensive. He offered a ten year guarantee (original owner).
> But there was much small print. *The amplifier had to be returned
> (freight at the owner's expense) for service, checking and maintenance
> at regular intervals.
I give a 12 month warranty on everything except tubes. If no work has
to be done in the first year I usually extend the warranty period a
year.

I have probably done 50 re-engineering jobs where amps and radios were
totally re-wired or built as new items and I've never had to repair
anything within a year except replace about 3 tubes - all since 1994.
Last year completely re-wired a pair of Ming Da 100W monos with 2 x
845. The original Chinese designer had been drinking far too much rice
wine when he designed it. OK, it gives no bother after the owner gets
it back but then a couple of the Chinese 2W resistors just go open for
no discernible reason, no heat stress, no color change, just open, and
only had 180Vdc across them. So OK, I agree to GO FURTHER and replace
24 Chinese resistors with other types of known metal film variety -
and this means re-designing-building new capacitor assemblies so
crucial R buried under horribly made boards must all be ripped out and
done again to allow future access without pain. Another few days of
work, not free of course. I cannot be fully responsible for things I
did not manufacture. So warranties are a good will thing, and I like
to keep ppl happy, but so far my work has stood up over time. The
essential thing which all tube amps must have to avoid smoke is active
protection against bias failure. All other amps except mine don't have
this feature; if one or more tubes conducts too much Iadc the amp
turns off automatically. Such a feature has saved my bacon a few
times after ppl have bought NOS tubes which all were fine for a month,
and then one or two began to arc internally. Once a Chinese EL34
heater lead became unsoldered in a tube base in a re-engineered ST70.
The other tube had to do all the work and the overload circuit Ia dc
trip circuit turned off the amp; the OPTs don't get cooked. The amp
took 20 minutes to fix and check all electrodes, done for free, The
guy is happy, and no big bill.

> Valves, power resistors, pots etc were changed
> long before they had reached the end of their active life. *Most of his
> clients were local, and he would provide a replacement amp if required
> while their own was being serviced.

Tube gear in hospitals and at airports had to be serviced with more
zeal than anywhere else.
>
> >But its not just old amps that fail. Companies
> >have techs to design gear using PC aided design programs and all is
> >simulated then manufactured without extensive tests in HOT ROOMS to
> >see what fails when things get hot. Nup, the consumer gets to be the
> >test guy these days. So I get stuff than went BANG at the first time
> >it was turned on, ****ed PT and CD player, totally inadequate
> >protection. One Emotiva amp destroyed one of its 5 x 200W channels
> >last week. No reason, just a bang, smoke, and silence. Filthy
> >complexity on the boards. Emotiva send a new amp module with board and
> >HS for free, and don't want the old one returned. This Chinese amp is
> >made so cheaply that accepting returns costs more than their
> >manufacture, so they charge a big price online, and they don't mind if
> >10% fail, they are way in front at the bank.
>
> Yes. I have always wondered what happened in the case of a
> Chinese amp that exhibited pyrotechnics, as most of them are
> bought direct, and not through a local dealer who would normally be
> responsible for warranty repairs.

Well, the local guy who bought an Emotiva amp with 5 x 200W channels
got it cheaper than anything else he could have bought in any store,
so he's ahead by thousands of bucks. Emotiva sent a new amp module for
free, no questions asked. He's going to ask Emotiva to pay my repair
bill. But its out of warranty. I said I could not give a warranty for
the amp module. OK, I hope there is no more smoke. But I'll not be
surprised if other modules fail.
>
> > The trouble is that nobody can pass laws requiring gear failure rates
> > to be under 1% over 5 years. Ah, the wonderful efforts of the Whatever
> > Generation!
>
> In broadcast and studios, bad news travels fast. So manufacturers
> do their best to keep the clients happy. That's the only was to get
> repeat high volume orders.

Ordinary consumers never get to know each other to the extent they
might pool their experiences. There are a vast range of amp choices,
so lemons don't get spotted. There is little FB effect on sales.

Patrick Turner.

>
> Iain- Hide quoted text -
>
> - Show quoted text -

Iain Churches[_2_]

June 16th 11, 04:46 PM

"Patrick Turner" > wrote in message
...

>Its obvious to me the STA 100W amp shown in the add is a
>"professional" amp not intended for home use.
>at 10/- per Watt, its cost was only 50 QUID.

Ermm. It's a stereo amp so 2 x 100 x 10shillings is
100 QUID. Actually the price was UKP 112, which
in those days was a month's salary (gross) for most
of us.

At the rate of 10 shillings/Watt, my small rented
apartment in London at that time cost me 6W.

Radford was one of the few companies that did
boards assembly, wiring, chassis fabrication,
paintshop and in particular transformer winding
"in-house", . Without having to use sub-contractors
and middle-men they could build more economically.

>However, there was NOTHING to stop anyone buying a couple of STA 100
>amps for home

Why a couple? It's a stereo amplfier.

> use and they were entirely free to modify them to be
> more reliable and have less distortion.

The THD at 100W was 0.1% which, at typical
domestic listening levels, was probably reduced by
an order of magnitude.

The STA100 that I have was built in 1966
It still has its BBC part number and revision
stickers on it.. I acquired it in perfect working
order in1987. It has been well maintained, and
still performs flawlessly, forty five years later.

I wonder how many of the users you refer to could
make modifications to improve either performance
or reliablilty?

>Who really needed to buy a Radford in 1967?

Well broadcasters and professional studios
had them in quantity.

Radford had a range of lower powered amplifiers
the STA15 and STA 25 for high end domestic use.
The latter was often seen in studio listening rooms also.

There were also mono versions of these amps, MA15
and MA25

Iain

Iain Churches[_2_]

June 16th 11, 04:49 PM

"flipper" > wrote in message
...

> No one said it was for 'home use'. It was offered as an example of
> "aother fine British valve/tube amp also used by the BBC."

As I mentioned elsewhere, Radford built other amplifiers,
the STA15 and STA 25 that were designed for home
use. In fact the STA25 also found its way into many
small studios, and was also used to power the BBC
Radford/Kef monitor speaker. The amp was clamped
to a shelf built into the bottom of the speaker stand
so that it would not get separated. It had a 25 Ohm
secondary to match the speaker impedance.

>
> Jackass Phil is being jackass Phil and blindly taking his
> characterization of things is a fool's errand.

Yes indeed.
>
>>Who really needed to buy a Radford in 1967?
>
> According to Iain, the BBC.

Yes. Decca too, and CBS, Island Records, etc etc

Iain

Iain Churches[_2_]

June 16th 11, 05:10 PM

"Patrick Turner" > wrote in message
...
>
>I've never worked for BBC, or Austraya's ABC or the private broadcast
>or show production networks or companies. Things do go astray in Oz,
>despite service staff, and for example, silence in the middle of radio
>programme is all too common.

There are so many links in the broadcast chain that can fail.
All too often it's not studio equipment but satelite news links etc.

Back the mid/late 80s, I was with a group from Scadinavian
Broadcasting visiting Thames TV in the UK. The company was
celebrating 20 years on the air. They were using Ampex VTRs
which (according to the Swedes) were not a patch on Sony in
terms of reliability. They told us that they had never had a
breakdown in transmission. Their service and maintenance
was impeccable. The (super-efficient) Swedish service guys were
greatly impressed by the way things were organised.
It can be done. And by comparison, looking after a few
valve amps in a radio studio compex is very straightforward
indeed.

>I give a 12 month warranty on everything except tubes. If no work has
>to be done in the first year I usually extend the warranty period a
>year.

Yes. That sounds fair. In this part of the world, dealers are willing to
extend warranties to two or perhaps five years (with provisions) for
a good valve amplifier. It's a good way to show confidence in the
engineering.

>Ordinary consumers never get to know each other to the extent they
>might pool their experiences. There are a vast range of amp choices,
>so lemons don't get spotted. There is little FB effect on sales.

Agreed. Although people are getting their opinions across, and more
widely know via Internet news and discussion groups.

Iain

Iain Churches[_2_]

June 16th 11, 05:11 PM

"flipper" > wrote in message
...
> On Thu, 16 Jun 2011 09:29:54 +0300, "Iain Churches"
> > wrote:
>
>>Of course it is not a PA amp, Flipper, although some may
>>have been sold for that application.
>
> Well, the point was Phil referenced this 'advert'
>
> http://www.saturn-sound.com/images%20-%20adverts/advert%20-%20radford%20sta100%20-%20hi-fi%20news%20-%20november%201967.jpg
>
> in which they specifically mention "rigorous public address work" and
> he used that to claim they 'admit' it's 'only a P.A. amp'

Agreed. The advert also refers to commercial and professional uses.
Broadcast and recording studios fall into both these categories, and
are no doubt the "reliable high quality permanent installations" to which
the copy writer refers:-)

> As one who's been involved in some sales blurbs myself it seems likely
> to me they were using the P.A. application to emphasize how rugged it
> was (by golly you can even let P.A. goons use it) but, whatever the
> reason, I was just saying it's disingenuous to selectively pick out a
> couple of words and ignore the rest.

Agreed.

> Besides the quote I referenced it's also worth noting the advert was
> in "Hi-Fi News" and the saturn-sound site has that in it's "Hi-Fi
> section."

It was also listed in the Hi-Fi Year Book and various professional
broadcast directories of the period. The fact that it was used by
the BBC and major UK studios, surely speaks for itself.

Iain

Iain Churches[_2_]

June 16th 11, 06:36 PM

"flipper" > wrote in message
...
> On Thu, 16 Jun 2011 18:49:58 +0300, "Iain Churches"
> > wrote:
>
>>
>>"flipper" > wrote in message
...
>>
>>> No one said it was for 'home use'. It was offered as an example of
>>> "aother fine British valve/tube amp also used by the BBC."
>>
>>As I mentioned elsewhere, Radford built other amplifiers,
>>the STA15 and STA 25 that were designed for home
>>use. In fact the STA25 also found its way into many
>>small studios, and was also used to power the BBC
>>Radford/Kef monitor speaker. The amp was clamped
>>to a shelf built into the bottom of the speaker stand
>>so that it would not get separated. It had a 25 Ohm
>>secondary to match the speaker impedance.
>
> Hmm. Interesting use of a 6U8. I'd not seen a half pentode half triode
> LPT/grounded grid phase inverter before.

Arthur Radford and Dr Bailey, wrote an interesting
article about this topology in Wireless World. It's a very good
series of amps, despite what Phil might say:-).

See:
http://en.wikipedia.org/wiki/Radford_Electronics

Iain

John L Stewart

June 17th 11, 01:34 AM

Hmm. Interesting use of a 6U8. I'd not seen a half pentode half triode
LPT/grounded grid phase inverter before.

>>>>Where is the link to that 6U8 cct? Sounds a bit like part of the DC amp used commonly in tubed regulated DC power supplies.

Cheers, John

Patrick Turner

June 17th 11, 02:18 AM

>
> >Who really needed to buy a Radford in 1967?
>
> According to Iain, the BBC.

Just because the BBC bean counters allowed the choice of amps, it does
not follow the amps were extraordinary or perfect. I don't much care
what the BBC or ABC or any other organisation did or did not use or
how many amps they bought or how many hamburgers the staff ate at
lunch.

I'm only interested in the amplifier under bonnet workings.

And hamburgers have to meet my criteria about nutrition before I eat
one.

Patrick Turner.

Patrick Turner

June 17th 11, 02:49 AM

On Jun 17, 1:46*am, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
>
> >Its obvious to me the STA 100W amp shown in the add is a
> >"professional" amp not intended for home use.
> >at 10/- per Watt, its cost was only 50 QUID.
>
> Ermm. *It's a stereo amp so 2 x 100 x 10shillings is
> 100 QUID. Actually the price was UKP 112, which
> in those days was a month's salary (gross) for most
> of us.

OK. 50 Quid a channel.

But if I go to Miranda Hi-Fi in my city Canberra, they have McIntosh
re-issue MC60 with 4 x KT88 and last time I saw the price a few years
back is was $4,300, and AWE were $769, so the 120Watts cost 5.6 week's
pay.

I'm not sure what MC75 cost in 1967. What did Quad and other brands
cost? I don't much give any care; its all ancient history; its over,
gone, and who really gives a ****?

>
> At the rate of 10 shillings/Watt, my small rented
> apartment in London at that time cost me 6W.

Ah, so you had to supply 6W to power the apartment? :-)
But here it cost $12, about similar, give or take 50%.

>
> Radford was one of the few companies that did
> boards assembly, wiring, chassis fabrication,
> paintshop and in particular transformer winding
> "in-house", . *Without having to use sub-contractors
> and middle-men they could build more economically.

But regardless of who worked on the amp or how the amp was produced
the issue is the circuit integrity.
You cannot hear economics and the THD meter can't measure economics.

>
> >However, there was NOTHING to stop anyone buying a couple of STA 100
> >amps for home
>
> Why a couple? *It's a stereo amplfier.

OK, but a rich ******* could buy a dozen, one for each room in the
house :--)
>
> > use and they were entirely free to modify them to be
> > more reliable and have less distortion.
>
> The THD at 100W was 0.1% which, at typical
> domestic listening levels, was probably reduced by
> an order of magnitude.

The 0.1% seems too good to be true, and probably due to larger than
normal amounts of NFB.
>
> The STA100 that I have was built in 1966
> It still has its BBC part number and revision
> stickers on it.. I acquired it in perfect working
> order in1987. It has been well maintained, and
> still performs flawlessly, forty five years later.
>
> I wonder how many of the users you refer to could
> make modifications to improve either performance
> or reliablilty?
>
> >Who really needed to buy a Radford in 1967?
>
> Well broadcasters and professional studios
> had them in quantity.

Such people needed big numbers and went to ppl who made big numbers. I
still maintain the recipe of the STA 100 is inappropriate for home hi-
fi and that a quad or six pack of OP tubes will perform better.

I know a bloke with 2 JBL studio monitor speakers each with 2 x 15"
woofers in a large box and a "bum shaped" horn for the tweeter and
sensitivity is around 96dB/W/M. He has 2 x Yamaha 2200 SS amps to
drive the speakers bi-amped. I mentioned a triode amp to him and he
quickly dismissed that Idea. He went to the gym to work out. He liked
amps to have muscle, speakers to be impressive, and I felt little need
to argue.
But his listening room was 12 feet long and 10 feet wide.

I think he uses about an average of 1/2 a watt total most days
although the amps could give 800W +.

One has to wonder if the BBC people who bought the higher power amps
really needed the power, or whether they talked themselves into it due
to their latent insecurity. After all, whoever made the buying
decisions were not spending their own money. If someone came along and
offered 1,000 watts a channel for a quid under Radford's price then
they would have become the supplier at the time.

Now there are SS amps coming from China and dirt cheap price per watt.
It doesn't mean I want one.

> Radford had a range of lower powered amplifiers
> the STA15 and STA 25 for high end domestic use.
> The latter was often seen in studio listening rooms also.
>
> There were also mono versions of these amps, MA15
> and MA25

Indeed. But there's always better than was done in the past. Most ppl
want that better.

Patrick Turner.

>
> Iain

Patrick Turner

June 17th 11, 03:03 AM

On Jun 17, 1:47*am, flipper > wrote:
> On Thu, 16 Jun 2011 01:34:24 -0700 (PDT), Patrick Turner
>
> > wrote:
>
> <snip>
>
>
>
> >> In broadcast and studios, bad news travels fast. So manufacturers
> >> do their best to keep the clients happy. That's the only was to get
> >> repeat high volume orders.
>
> >Ordinary consumers never get to know each other to the extent they
> >might pool their experiences. There are a vast range of amp choices,
> >so lemons don't get spotted. There is little FB effect on sales.
>
> Speak for yourself.
>
> There are a vast array of 'feedback' resources from individual
> 'Internet reviews', to trade and consumer magazines, to time honored
> compilations like consumer reports.

The vast majority of ppl who buy bread and butter budget models of
consumer goods do not spend time seraching the internet for reviews on
such things and in forums. They do not get the chance to talk to 10
ppl who have owned what they consider buying for several years. They
just go to a store, and end up taking a risk on something that fits
their wallet. Maybe their dad bought a Yamaha, so son buys Yamaha. Dad
had Cerwin Vega speakers, and sone wants Cerwin Vega, and now Cerwin
Vega offer far bigger speakers than Dad could have bought in 1978.
Nobody who brings me Yamaha or Cerwin Vega speakers to to me for
repair ever tell me about their searches for reviews or peer group
forums; they consider most info to be BS anyway.

People's mums bought Hover washing machines made in Oz in the 1970s.
My departing feckless ex-wife took the Hoover when she vanished one
day while I was at work. Next day I bought another Hoover. ****in good
stuff, not too many fixes needed which I could not do myself. Goes
like a trooper, 33 years old, no major parts replacements.

Probably there was no need of the Internet in 1978.

Patrick Turner.

Patrick Turner

June 17th 11, 03:08 AM

On Jun 17, 2:10*am, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
>
>
>
> >I've never worked for BBC, or Austraya's ABC or the private broadcast
> >or show production networks or companies. Things do go astray in Oz,
> >despite service staff, and for example, silence in the middle of radio
> >programme is all too common.
>
> There are so many links in the broadcast chain that can fail.
> All too often it's not studio equipment but satelite news links etc.
>
> Back the mid/late 80s, I was with a group from Scadinavian
> Broadcasting visiting Thames TV in the UK. *The company was
> celebrating 20 years on the air. *They were using Ampex VTRs
> which (according to the Swedes) were not a patch on Sony in
> terms of reliability. They told us that they had never had a
> breakdown in transmission. *Their service and maintenance
> was impeccable. The (super-efficient) Swedish service guys were
> greatly impressed by the way things were organised.
> It can be done. *And by comparison, looking after a few
> valve amps in a radio studio compex is very straightforward
> indeed.
>
> >I give a 12 month warranty on everything except tubes. If no work has
> >to be done in the first year I usually extend the warranty period a
> >year.
>
> Yes. That sounds fair. *In this part of the world, dealers are willing to
> extend warranties to two or perhaps five years (with provisions) for
> a good valve amplifier. *It's a good way to show confidence in the
> engineering.
>
> >Ordinary consumers never get to know each other to the extent they
> >might pool their experiences. There are a vast range of amp choices,
> >so lemons don't get spotted. There is little FB effect on sales.
>
> Agreed. *Although people are getting their opinions across, and more
> widely know via Internet news and discussion groups.
>
> Iain

Nowdays quite a few manufacturers go into and out of business over a
short time. Probably Yamaha, Sony, Denon are around for the long haul
but there are lots of makers of tube stuff who are here today and gone
tomorrow. Some make good stuff which anyone can service, and some
don't. In 10 years when I'm dead who will wind a replacement OPT for
amps I made? Its a reason why I fit active protection to avoid ****
happening in 10 years.

Patrick Turner..

Iain Churches[_2_]

June 17th 11, 07:49 AM

"John L Stewart" > wrote in message
...
>
> Hmm. Interesting use of a 6U8. I'd not seen a half pentode half triode
> LPT/grounded grid phase inverter before.
>
>Where is the link to that 6U8 cct? Sounds a bit like part of the DC
> amp used commonly in tubed regulated DC power supplies.
>

John. the STA25 is here:

http://www.freeinfosociety.com/electronics/schemview.php?id=2362

Iain

Iain Churches[_2_]

June 17th 11, 08:35 AM

"flipper" > wrote in message
...
> On Thu, 16 Jun 2011 20:36:15 +0300, "Iain Churches"
> > wrote:
>
>>
>>"flipper" > wrote in message

>>> Hmm. Interesting use of a 6U8. I'd not seen a half pentode half triode
>>> LPT/grounded grid phase inverter before.
>>
>>Arthur Radford and Dr Bailey, wrote an interesting
>>article about this topology in Wireless World. It's a very good
>>series of amps, despite what Phil might say:-).
>>
>>See:
>>http://en.wikipedia.org/wiki/Radford_Electronics

> It's cool they mention it but I want the article!

I have it somewhere, with a million other articles.
It's just a matter of finding it. I will do my best.

Regards
Iain

Iain Churches[_2_]

June 17th 11, 08:35 AM

"Patrick Turner" > wrote in message
...

>I'm not sure what MC75 cost in 1967. What did Quad and other brands
>cost?

Here are some UK retail prices in UKP from 1968:

Dynaco ST-35 £40.19s
Dynaco ST-70 £59.17s
Kerr McCosh CWA2/12Wpc £48.
Kerr McCosh CWA40 (40W Monobloc) £45
Leak Stereo 30 (transistorised) £58.10s
Leak Stereo 70 (ditto) £69.10
Leak Point One (valve) 30Wpc £45
Lowther L18S £47
Radford STA15 £42.10s
Radford STA25 £52.10s
Radford STA100 £112
Quad II (12Wpc) £25
Shirley Laboratories 25W stereo £52
Vortexion 100W (silicon) £70

With people earning £20 per week, you can draw
your own conclusions. It is not surprising that as
available power increases, the cost per watt
decreases. With the exception of the Dynaco,
all theamplifiers loisted above were made in the UK.
The Quad II was the cheapest, by far.

> At the rate of 10 shillings/Watt, my small rented
> apartment in London at that time cost me 6W.

Ah, so you had to supply 6W to power the apartment? :-)
But here it cost $12, about similar, give or take 50%.

> You cannot hear economics and the THD meter can't measure economics.

Agreed. I have no doubt that major customers took
some units for listening evaluation by some of the best
ears in the business. Next the units would be handed over
to the technical boffins for technical evaluation, performanc, build
quality and reliability. Then all of these parameters including of course
the price would be compared with other available products, and a
choice would be made.

>
> >However, there was NOTHING to stop anyone buying a couple of STA 100
> >amps for home
>
> Why a couple? It's a stereo amplfier.

> The THD at 100W was 0.1% which, at typical
> domestic listening levels, was probably reduced by
> an order of magnitude.

The 0.1% seems too good to be true, and probably due to larger than
normal amounts of NFB.

It's true. Measured by customers and reviewer, and published
by the manufacturer.

> >Who really needed to buy a Radford in 1967?
>
> Well broadcasters and professional studios
> had them in quantity.

>Such people needed big numbers and went to ppl who made big numbers.

They went primarily for a high power high performance reliable amp.

>I still maintain the recipe of the STA 100 is inappropriate for home hi-
>fi and that a quad or six pack of OP tubes will perform better.

Patrick. The STA100 was *never* intended, nor marketed
for home hi-fi. The STA15 and STA25 were designed for
domestic use.

Iain

Iain Churches[_2_]

June 17th 11, 08:36 AM

"Patrick Turner" > wrote in message
...
On Jun 17, 1:46 am, "Iain Churches" > wrote:

Patrick
>> >Who really needed to buy a Radford in 1967?
>
Iain
>> Well broadcasters and professional studios
>> had them in quantity.

>Such people needed big numbers and went to ppl who made big numbers.

Huge quantities were not ordered for immediately delivery, but say
X units a month over 2 years. I bet that even you would pull out all
the stops if you could win an order ike that, Patrick:-)))

I can remember visitng the Leak factory in Acton, London W3, with
my Dad circa 1955 when we took his TL12 for service (which they did
while we waited and drank tea in the reception area) The place was
pretty small. I can remember about 12-15 women wearing bright
aprons and floral headscarves on the assembly bench, There was a
storeage area, a listening room and two or three "lab type" rooms
with people in white coats. It was quite a nice art deco building on
an industrial state, probably long demolished. I was expecting
something much bigger.

Radford has about 120 people working at Ashton Vale Bristol
when I went there mid 60s. They did everything in house, including
transformer windings. There were three machines. We were even
shown "Radford's Book" where all the winding info had been entered.
There were several buildings, metal fabrication, paint shop, amp
assembly, tuner assembly, test, R+D, and offices.

The firm closed after Arthur Radford died, but Wayne Kerr took over
the manufacture of Radford's lab equipment, the LDO (low distortion
oscillator) the Psophometer, and waveform analyser.

I forgot to mention that Radford also made a "reference standard"
power amplfier, the ISTA which was not available to the public.
It was used by universities, research labs, and speaker manufacturers.

In 2006 an announcement was made that a new company using the
name Radford Electonics would start to build the STA series valve
amps again using the same Radford logo. There were legal
complications, and nothing came of it.

Iain

Patrick Turner

June 17th 11, 10:12 AM

On Jun 17, 5:35*pm, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
>
> >I'm not sure what MC75 cost in 1967. What did Quad and other brands
> >cost?
>
> Here are some UK retail prices in UKP from 1968:
>
> Dynaco ST-35 40.19s
> Dynaco ST-70 59.17s
> Kerr McCosh CWA2/12Wpc 48.
> Kerr McCosh CWA40 (40W Monobloc) 45
> Leak Stereo 30 (transistorised) 58.10s
> Leak Stereo 70 (ditto) 69.10
> Leak Point One (valve) 30Wpc 45
> Lowther L18S 47
> Radford STA15 * 42.10s
> Radford STA25 * 52.10s
> Radford STA100 112
> Quad II (12Wpc) 25
> Shirley Laboratories 25W stereo 52
> Vortexion 100W (silicon) * 70

Quad-II does more than 12W/channel, more like 22W, so
comparable to the STA25, but 1/2 the price.

You said Radford did everything in house to get costs lower, but they
charged more.

Still, who cares now?

Try to buy a Quad Eighty now. Boyo boy, chinese made with Chinese
costs at 64c/Hr for labour, and maybe IAG who own the QUad name are
related to the Chinese Commutits Party. I guess Quad or whoever they
really are, are making up for lost time.

> With people earning 20 per week, you can draw
> your own conclusions. It is not surprising that as
> available power increases, the cost per watt
> decreases. *With the exception of the Dynaco,
> all theamplifiers loisted above were made in the UK.
> The Quad II was the cheapest, by far.
>
> > At the rate of 10 shillings/Watt, my small rented
> > apartment in London at that time cost me 6W.
>
> Ah, so you had to supply 6W to power the apartment? :-)
> But here it cost $12, about similar, give or take 50%.
>
> > You cannot hear economics and the THD meter can't measure economics.
>
> Agreed. I have no doubt that major customers took
> some units for listening evaluation by some of the best
> ears in the business. Next the units would be handed over
> to the technical boffins for technical evaluation, performanc, build
> quality and reliability. Then all of these parameters including of course
> the price would be compared with other available products, and a
> choice would be made.

Yeah, blah blah blah but still I find lots of things in STA100 and
other radfords I would definately have done differently, and better,
but trying to assert that in 1967 against egotesticalated company
leaders could get you sacked. >
>
> > >However, there was NOTHING to stop anyone buying a couple of STA 100
> > >amps for home
>
> > Why a couple? It's a stereo amplfier.
> > The THD at 100W was 0.1% which, at typical
> > domestic listening levels, was probably reduced by
> > an order of magnitude.
>
> The 0.1% seems too good to be true, and probably due to larger than
> normal amounts of NFB.
>
> It's true. Measured by customers and reviewer, and published
> by the manufacturer.

Must be huge ampunt of NFB. It wasn't unusual for a number of
companies to have 30dB GNFB in tube amps so when the dick swinging
comparisons began someone could say
"well my amp has less THD than yours" etc.....

So claims for THD lowness mean SFA to me, unless the amount of NFB in
comparisons is the SAME.

If there was only 20dB GNFB instead of 30dB, expect 0.3% THD. Not so
hot but quite OK because at 2 watts it would have been about 0.04%
like so many other UL tube amps with similar levels of GNFB.

Using Ea = 600Vdc and with Eg2 at the same level because g2 connect to
the anode UL tap then methinks one might not want to use 6550, and
you'd have to use KT88, and I worry about those made now with EA = Eg2
= 600V.

Nothing you have said will change my view that a quad of 6L6GC would
be superior in every way to a pair of KT88.

> > >Who really needed to buy a Radford in 1967?
>
> > Well broadcasters and professional studios
> > had them in quantity.
> >Such people needed big numbers and went to ppl who made big numbers.
>
> They went primarily for a high power high performance reliable amp.
>
> >I still maintain the recipe of the STA 100 is inappropriate for home hi-
> >fi and that a quad or six pack of OP tubes will perform better.
>
> Patrick. The STA100 was *never* intended, nor marketed
> for home hi-fi. *The STA15 and STA25 were designed for
> domestic use.

Sure, but read my lips... STA100 *could -have - been - used - for -
domestic - audio.*

These days a 15W or 25W amp is a bit low on power for modern speakers
requiring 4 times the power needed for more sensitive speakers made in
1960s.

Patrick Turner.

>
> *Iain

Iain Churches[_2_]

June 17th 11, 10:32 AM

"Patrick Turner" > wrote in message
...

> Quad-II does more than 12W/channel, more like 22W, so
> comparable to the STA25, but 1/2 the price.

And Phil thought the Radford was cheap !!! LOL:-)

According to the spec I have before me (Hi Fi Year Book)
Quad II is quoted at 15W. Distortion 3rd harmonic and
higher is given as 0.1% at 12W

So if we are to compare apples with apples and use
0.1% as a standard as Radford did, then the Quad II
is a 12W amp.

>> Patrick. The STA100 was *never* intended, nor marketed
>> for home hi-fi. The STA15 and STA25 were designed for
>> domestic use.

>Sure, but read my lips... STA100 *could -have - been - used - for -
>domestic - audio.*

Just as an Aston Martin could be used for pizza delivery

Cheers
Iain

Patrick Turner

June 17th 11, 10:34 AM

On Jun 17, 5:36*pm, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
> On Jun 17, 1:46 am, "Iain Churches" > wrote:
>
> Patrick
>
> >> >Who really needed to buy a Radford in 1967?
>
> Iain
> >> Well broadcasters and professional studios
> >> had them in quantity.
> >Such people needed big numbers and went to ppl who made big numbers.
>
> Huge quantities were not ordered for immediately delivery, but say
> X units a month over 2 years. *I bet that even you would pull out all
> the stops if you could win an order ike that, Patrick:-)))

To win a contract like that you'd need to know the right ppl in the
right places plus show you had already established a factory which
could increase production numbers.

To repeat anything like what happened in 1960s is utterly impossible.
I'm 50 years too late. I'd have needed venture capital and a team and
so on. Not now, ppl just go to China.

> I can remember visitng the Leak factory in Acton, London W3, with
> my Dad circa 1955 when we took his TL12 for service (which they did
> while we waited and drank tea in the reception area) * The place was
> pretty small. *I can remember about 12-15 women *wearing bright
> aprons and floral headscarves on the assembly bench, There was a
> storeage area, a listening room and two or three "lab type" rooms
> with people *in white coats. It was quite a nice art deco building on
> an industrial state, probably long demolished. I was expecting
> something much bigger.
>
> Radford has about 120 people working at Ashton Vale Bristol
> when I went there mid 60s. *They did everything in house, including
> transformer windings. *There were three machines. *We were even
> shown "Radford's Book" where all the winding info had been entered.
> There were several buildings, metal fabrication, paint shop, amp
> assembly, tuner assembly, test, *R+D, and offices.

All very impressive nostalgia.
>
> The firm closed after Arthur Radford died, but Wayne Kerr took over
> the manufacture of Radford's lab equipment, the LDO (low distortion
> oscillator) the Psophometer, and waveform analyser.
>
> I forgot to mention that Radford also made a "reference standard"
> power amplfier, the ISTA which was not available to the public.
> It was used by universities, research labs, and speaker manufacturers.
>
> In 2006 an announcement was made that a new company using the
> name Radford Electonics would start to build the STA series valve
> amps again using the same Radford logo. *There were legal
> complications, and nothing came of it.

Not much in Google about Radford RFTD amp models, (Raised from The
Dead)

Manufacturing tube amps in western countries is a big risk because Mr
China gives a better price to Joe Public who has loyalty to low
prices, and not to any brand name. Mr Western Middleman still takes
the lion's share of the retail price.

Tube amps all have essentially very simple and similar circuits with
similar amounts of THD if the loadings for the class of operation and
amount of GNFB plus any local NFB is the same. Hence a Chinese made
tube amp can measure equally well to anything made in the UK, and now
sometimes the quality of some supposedly UK made amps may be far worse
than something made made in China.

So, when I inevitably have to examine other makers amps turning up
here for de-smoking and singing lessons I find very little to get
excited about, and a lot which would cause depression in other techs.

It seems to me there are plenty of tube amps made by companies in
which not a single man has read RDH4.

Patrick Turner.

>
> Iain

Iain Churches[_2_]

June 17th 11, 11:03 AM

"Patrick Turner" > wrote in message
...
On Jun 17, 5:36 pm, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
> On Jun 17, 1:46 am, "Iain Churches" > wrote:
>
>> Huge quantities were not ordered for immediately delivery, but say
>> X units a month over 2 years. I bet that even you would pull out all
>> the stops if you could win an order ike that, Patrick:-)))

>To win a contract like that you'd need to know the right ppl in the
>right places plus show you had already established a factory which
>could increase production numbers.

These days many firms are kick-started on venture capital.
If you can convince a major potential client regarding the
product you are proposing to build.

I can think of many examples, most of which started out a
shirtcuff sketches. The British are pretty good at that sort
of thing but somehow they don't seem to be able to sustain
the momentum to follow through.

>> In 2006 an announcement was made that a new company using the
>> name Radford Electonics would start to build the STA series valve
>> amps again using the same Radford logo. There were legal
>> complications, and nothing came of it.

>Not much in Google about Radford RFTD amp models, (Raised from The
>Dead)

No. They contacted me a an early stage. There were lots of news
bulletins sent to potential investors and other interested parties.
But product demonstration deadlines came and went with nothing
to show. Then silence.

I am pretty sure I know what the reason was......

Iain

Patrick Turner

June 17th 11, 11:21 AM

On Jun 17, 8:03*pm, "Iain Churches" > wrote:
> "Patrick Turner" > wrote in message
>
> ...
> On Jun 17, 5:36 pm, "Iain Churches" > wrote:
>
> > "Patrick Turner" > wrote in message
>
> ....
> > On Jun 17, 1:46 am, "Iain Churches" > wrote:
>
> >> Huge quantities were not ordered for immediately delivery, but say
> >> X units a month over 2 years. I bet that even you would pull out all
> >> the stops if you could win an order ike that, Patrick:-)))
> >To win a contract like that you'd need to know the right ppl in the
> >right places plus show you had already established a factory which
> >could increase production numbers.
>
> These days many firms are kick-started on venture capital.
> If *you can convince a major potential client regarding the
> product you are proposing to build.
>
> I can think of many examples, most of which started out a
> shirtcuff sketches. * The British are pretty good at that sort
> of thing but somehow they don't seem to be able to sustain
> the momentum to follow through.

The high Oz dollar and shipping costs would kill profits I could make
manufacturing tube amps in large numbers here in Oz while I paid high
Oz costs for every damn thing.

Tube amps are niche products, not mainstream.

And I'm too ****in' old to want to **** up a nice life by working 80
hours a week to make it all happen, even if I could get venture
capital. Usually such venturists would want to take out a mortgage on
my house so they don't really venture or take much of a risk, they
just charge a yet another big cost on business.

The commercial historty of tube amp makers in Oz is littered with ppl
who have gone broke.

If I was 25, and had no money, then fine, going broke just loses
someone else's money, and they can't get blood from a stone. I've met
young blokes who have had **** happen despite huge hard work and
finance backing and a good product. One made snow boards. After that
failed he lived in a VW kombi for 2 years and moved around to stop
the creditors getting his beat up kombi and the shirt from his back. I
could smell him coming because he never had anywhere to wash his
clothes or himself. But finally he recovered a bit and went to the UK
to work where he's started a new life and although he works for the
man he has autonomy, and is doing real well. Ben was heavily into
alternative music, and would need advice about crazy electronics he
dabbled with. He was a born dreamer, alas, not always practical.

> >> In 2006 an announcement was made that a new company using the
> >> name Radford Electonics would start to build the STA series valve
> >> amps again using the same Radford logo. There were legal
> >> complications, and nothing came of it.
> >Not much in Google about Radford RFTD amp models, (Raised from The
> >Dead)
>
> No. *They contacted me a an early stage. *There were lots of news
> bulletins sent to potential investors and other interested parties.
> But product demonstration deadlines came and went with nothing
> to show. Then silence.
>
> I am pretty sure I know what the reason was......

No demand?

Price way too high?

Trouble with unions?

Conducting Business is one damn thing after another.

Patrick Turner.
>
> Iain

Patrick Turner

June 17th 11, 12:18 PM

I said....
> The 0.1% seems too good to be true, and probably due to larger than
> normal amounts of NFB.

You repeated....
> It's true. Measured by customers and reviewer, and published
> by the manufacturer.

A quick look at the STA-100 shows that probably 40Vrms is needed to
drive each KT88 grid for 100W at 8 ohms where there would be 28Vrms.

The LTP with EF184 probably has a gain of 100, so only 0.8Vrms is
needed to produce Va-a = 80Vrms.
The cascode 6DJ8 has gain around 27 for the top tube and maybe 2 for
bottom tube. There is some local current FB for the bottom tube which
has very low Cin. I've estimated that without NFB only 0.04Vrms of
input is needed for 100W output and that the NFB network delivers 20dB
of NFB and input then needed is 0.4Vrms. Tally with your spec sheets?

So if there is indeed 0.1% at 100W with what must be 8 ohms, then
that's not bad, but perhaps all is not quite clear, and that although
100W is available the 0.1% occurs with a 16 ohm load. There is no
mention of 4 ohm loads, or any other load matches apart from the 100V
so the schematic I have is rather deficient, so what did Radford
conceal rather than explain fully in his schematic?

In all my tests of amps only those with 12% to 20% CFB in the OP stage
and lots of class A working ever give less than 1% THD without global
NFB, so that with 20dB GNFB you get D < 0.1%.
Typcal UL amps with low class A and high B portion typically give 4%
with no CFB and no GNFB.

Its possible the 3H created in the EF184 LTP has opposite phase to the
3H in output stage and some cancelling of 3H goes on. Unlikely though,
as most amps 3H is the effect of the flattening of the peaks on waves
where the voltage never quite makes it to where its supposed to get to
before it changes in direction at sine wave peaks.

I'd have preferred to use the EF184 in triode mode and taken one grid
to 0V and a common cathode R down to say -200V which would have been
easy; Radford had already dumped tube rectifiers from their circuits.
The triode LTP would still have had good gain if RL was high enough
because the EL184 triode µ = 60, and Ra = 12k, much lower/better than
running the darn things in pentode with all those extra biasing
networks as shown.
There is no real need for a cascode input stage at all.
A paralleled 6DJ8 would have been fine. No need for a gain pot at
input; the gain should be controlled in a preamp. I prefer the drive
amp I use in my 8585. See Fig 1 on the page at
http://www.turneraudio.com.au/8585-amp-october-2006.html

EL84 in triode are unsurpassable drivers IMHO.

BTW, I recently re-engineered a pair of 100W Ming Da monoblocs and the
input tube was SRPP 6SN7 which I changed to simpler paralleled input
triodes. I used a very similar LF shelving network to Radford's shown
after his cascode to prevent LF instability. So of course Radford and
I share some ideas, except that I used the network he has to direct
couple a following LTP with 6SN7, with longer tail R and usual 1M from
grid to grid and 2uF to 0V to ground the dead grid. The Ming Da have
a balanced amp with a pair of 300B following 6SN7 LTP to get enough
drive for up to 140Vrms at each 845 grid. The 300Bs are "over the top"
but were used to make the amp look spectacular. But it works OK, even
with only 7mA in each 300B. It was only 4mA when I first looked at it.
More could be done, but it sounds excelent, and not a single darn
pentoad to be seen anywhere.

There are simpler and better ways to to design an input & driver stage
than what Radford uses.

Patrick Turner.

John L Stewart

June 18th 11, 01:47 AM

;933429']"John L Stewart" > wrote in message
...
>
> Hmm. Interesting use of a 6U8. I'd not seen a half pentode half triode
> LPT/grounded grid phase inverter before.
>
>Where is the link to that 6U8 cct? Sounds a bit like part of the DC
> amp used commonly in tubed regulated DC power supplies.
>

John. the STA25 is he

http://www.freeinfosociety.com/electronics/schemview.php?id=2362

Iain

Thanx for that link Iain. Very odd cct, but similar to a common application in the DC FB amp used in the error amp of a tubed reg PS. Looks like they have both HF & LF shelf at the EF86 anode.

But the 6U8 pentode screen does not return to the cathode. It is AC bypassed to the common rail. The extra time constant probably complicates things. Will have to try it sometime.

Cheers, John

Trevor Wilson[_3_]

June 18th 11, 02:03 AM

Phil Allison wrote:

>
> Was Arthur Radford a " penny pincher " ???

**Maybe. IME, however, Radford built crossovers for his speakers that far
eclipsed the KEF crossover, that were used for the same drivers (B139, B110,
T27). In 1974 I built a pair of Bailey designed transmission lines, based on
the above KEF drivers. Bailey suggested the use of Radford crossovers for a
modest sonic improvment. The improvement was far from modest. Radford used
hefty air core inductors (rather than the crappy ferrite cored KEF ones and,
most interestingly, a parallel LC network to cure a resonance problem with
the B110 (that KEF never bothered to sort out 'till much later). The Radford
crossovers were impressive beasts, compared to the KEF ones, both visually
and sonically.

Was Radford a penny-pincher?

Not with crossovers.

--
Trevor Wilson
www.rageaudio.com.au

Phil Allison[_3_]

June 18th 11, 07:43 AM

"John L Stewart"

>> John. the STA25 is he
>>
>> http://www.freeinfosociety.com/electronics/schemview.php?id=2362

** Look, look, lookie - there is a filter choke in the PSU that feeds the
OP tranny.

So noooooo amplitude modulation !!!

And no stupid, damn zener diode in the bias supply.

BTW:

One of these came across my bench back in 1980 for a full overhaul.

..... Phil

Patrick Turner

June 23rd 11, 02:15 AM

> I am always amazed at how you arrogantly imagine to know what "the
> vast majority of ppl" think or do; especially since, by your own chest
> thumping, you and 'the vast majority of ppl" have nothing in common.

You are out of touch with the vast majority.

I have no dents on chest and never thump it.

I am aware of what my customers tell me.

Most of my customers represent the vast marority, representiatives of
the average person.

I'd never buy what most of them bring to me for a repair. Sure, I
don't have much in common with the vast majority of average ppl
earning an average $44,000 wage and buying all of whatever they buy.
But it does not mean I don't understand them fairly well. I try to
treat everyone like a king or queen, but its not always doable or
justified.

>
> > who buy bread and butter budget models of
> >consumer goods do not spend time seraching the internet for reviews on
> >such things and in forums. They do not get the chance to talk to 10
> >ppl who have owned what they consider buying for several years. They
> >just go to a store, and end up taking a risk on something that fits
> >their wallet. Maybe their dad bought a Yamaha, so son buys Yamaha. Dad
> >had Cerwin Vega speakers, and sone wants Cerwin Vega, and now Cerwin
> >Vega offer far bigger speakers than Dad could have bought in 1978.
>
> Speak for yourself, paleface. Recently I thought about getting a dirt
> cheap 'decent' SW portable receiver and the first thing I did was look
> for reviews and 'comparison shootout' articles. Now, we could imagine
> I'm a one off genius but if that were the case there'd be nothing for
> me to find, but there's a whole world of things to find.

You'd be a minority. And genius you ain't !!!!!!!!

If everyone had the same mind, only one variety of goods or service
would ever sell.

But most ppl just go to a store for a CD player and take the advice of
a sales person. I don't know a single person who ever listens to SW.
And don't forget that reviews can be a pack of lies.

I knew one man who'd spend days in agony checking out 59 different
brands of sleeping bag before going on a camping trip. Everything he
chooses to buy is a result of an epic search. It took several weeks to
find what he thought was a good deal for a mountain bike. But he's
fat, un-healthy, a bloody great bore, and he's getting worse with age.
When he went to a restaurant, he'd want to chat with the staff for 30
minutes and change te menu. I breathed a sigh of relief when he moved
town because this one wasn't good enough for him. But the quality of
his services fixing computers was so bad that a couple of guys tried
to sue his arse off, and a couple just refused to pay him. The PC he
assembled for me went phut after a few months. He charged me $1,800.
Later I found the parts he'd used were all old, and I could have
bought a working PC just as good in a clearence shop for $200. The
guy is an inconsistent fraud. I'm just wondering how you'd compare to
this guy.

Fortunately, most ppl only take 2 minutes to order a meal at a
restaurant, 20 minutes to buy a CD player.

>
> The fact that there are thousands of resources on everything
> imaginable disproves your 'theory'.
>
> >Nobody who brings me Yamaha or Cerwin Vega speakers to to me for
> >repair ever tell me about their searches for reviews or peer group
> >forums; they consider most info to be BS anyway.
>
> Maybe they don't care to waste their time talking to a brick wall but,
> whatever their reason, the handful of select people bringing you
> broken equipment hardly represents "the vast majority of ppl."

I've had hundreds cross my threshold. None have told me about their
long search for the best amp or CD player. Except one, the guy I
mentioned above. He phoned me twice a week for 2 months during two
consecutive years about the purchase of a pair of tube amps worth
$3,000. He bought chinese amps amps for $200 cheaper. The **** wasted
days of my time. He's the exception. But are you like that?

> You claming to know what "the vast majority of ppl" do based on the
> few who bring you broken things is like a heart surgeon claiming "the
> vast majority of ppl" need bypass surgery because the ones who come to
> him do. And I dare say he has a larger sample size.

The vast majority of ppl have hearts, right, but we all know a
minority will need a bypass.

Doctors don't hear stories about where ppl bought their hearts,
although some patients have ended up with a cold lump of stone after
shopping for a heart all those years ago. You analogy is absurd.
>
> >People's mums bought Hover washing machines made in Oz in the 1970s.
> >My departing feckless ex-wife took the Hoover when she vanished one
> >day while I was at work. Next day I bought another Hoover. ****in good
> >stuff, not too many fixes needed which I could not do myself. Goes
> >like a trooper, 33 years old, no major parts replacements.
>
> Is that supposed to be a 'review' that "the vast majority of ppl" will
> not bother with?

Weel, a lotta customers buy what their parents have owned. My mum has
now been through about 4 washing machines in the last 20 years. She
takes the advice of anyone she considers honest. I don't decide things
like that for her. But my washer is still running fine after 33 years.
I'm on my 4th motor vehicle since 1975, not including motorcycles. But
I know ppl who go have to replace gear far more often than I do. I'm
not aware they make a better choice than I do.

> >Probably there was no need of the Internet in 1978.
>
> People made do with the resources at hand. Now there are more. This is
> called "progress."

To where? oblvion? Don't worry, genetic engineering research is
underway and ppl will soon to be able to eat their own poop so bean
counters can't stress out over the costs of food. Diet recommendations
by Bean Counters can work wonders for some. Ppl need to be able to
breathe in CO2 and exhale O2. Rubbish piles up and up, and should be
re-cycled, so open your mouths everyone, and run it through again. And
sure there is progress, I agree with you on that, but to be smug and
content about its quality is to have the mind of a moron. I just pass
on most opportunities to buy stuff which won't last despite reviews, I
won't buy stuff to make me feel better, usually it don't, and I have
nobody I need to impress for stupid vain reasons. I am a marketeer's
disaster zone. Basically nobody can sell me anything much at all. I'm
very successful at avoiding expenses and silly habits. I could say I
have benfitted from is the evolution of medical knowhow and the
democratic process in Australia. But If I still needed a horse and
buggy and the bicycle hadn't been invented, life would still be OK, as
the Mormons have shown. Maybe I'd be a specialist in cart wheel
repairs. I cannot just say how wonderful everything is about modern
life without wearing out the air pointing out so many things that are
a PITA.

Patrick Turner.