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#1
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QUAD [1] Original booklet reproduced at Jute on Amps
QUAD [1] Original booklet reproduced at Jute on Amps:
http://coolmainpress.com/ELECTRONICS...20booklet.html Enjoy! Andre Jute |
#2
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"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 he 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 |
#3
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"Phil Allison" Meanwhile, schematic he 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.stereo...0seriesamp.htm.... Phil |
#4
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"Phil Allison" Meanwhile, schematic he 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.stereo...0seriesamp.htm ..... Phil |
#5
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
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 he 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. |
#6
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
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 he 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 - |
#7
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"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 |
#8
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"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 he 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 |
#9
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"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 |
#10
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
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 |
#11
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
"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 |
#12
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
" 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 |
#13
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
?
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. |
#14
Posted to rec.audio.tubes
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Arthur Radford a Penny Pincher?
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. |
#15
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Arthur Radford a Penny Pincher?
"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 |
#16
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Arthur Radford a Penny Pincher?
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/ |
#17
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Arthur Radford a Penny Pincher?
"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 |
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Arthur Radford a Penny Pincher?
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/ |
#19
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Arthur Radford a Penny Pincher?
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. |
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Quote:
Cheers, John |
#21
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Arthur Radford a Penny Pincher?
"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 |
#22
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Arthur Radford a Penny Pincher?
"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 |
#23
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Arthur Radford a Penny Pincher?
"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%2...ber%201967.jpg 100 volt line output ?? Under 10 shillings a watt in 1968 ?? Piece of ****. ..... Phil |
#24
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Arthur Radford a Penny Pincher?
"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%2...ber%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 |
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Arthur Radford a Penny Pincher?
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. |
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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. |
#27
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Radford SA100
"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 |
#28
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Preventative maintenance
"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 |
#29
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Preventative maintenance
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 - |
#30
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Radford STA100
"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 |
#31
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Radford SA100
"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 |
#32
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Preventative maintenance
"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 |
#33
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Radford STA100
"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%2...ber%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 |
#34
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Radford STA100
"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 |
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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 |
#36
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Radford SA100
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. |
#37
Posted to rec.audio.tubes
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Radford STA100
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 |
#38
Posted to rec.audio.tubes
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Preventative maintenance
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. |
#39
Posted to rec.audio.tubes
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Preventative maintenance
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.. |
#40
Posted to rec.audio.tubes
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QUAD [1] Original booklet reproduced at Jute on Amps
"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/elect...ew.php?id=2362 Iain |
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