Re: The QUAD I amplifier

[mike s]

On Saturday, June 11, 2011 11:04:53 AM UTC+1, Phil Allison wrote:
> "Iain Churchus"
> >"Phil Allison"
> >> In 1951 in the UK, there were no FM broadcasts, no stereo and the just
> >> about the only records available were 78rpm and pickups were crude to say
> >> the least.
> >>
> >>> just about the only records available were 78rpm and pickups were crude
> >>> to say the least.
> >
> > Not quite, Phil
> >
> > 10" LPs had been available in the UK since 1951,
>
>
> ** So did the chicken or the egg come first ?
>
> In any case, the performance of the early LEAK and QUAD hi-fi amps were
> orders of magnitude ahead of the signal sources available to non
> professionals in the early 1950s and for much longer.
>
> In fact, the same amps are not out of place in a modern domestic system -
> if fully restored to their past glory.
>
> THD figures of 0.05% and s/n ratios of - 97 dB are still excellent and
> better than most sources.
>
> Did Harold and Peter fully realise how far ahead of the game they were ??
>
>
>
> .... Phil

I have copies of just about every Wireless World magazine from 1934 to 1952.. It's quite apparent that there was a great deal of interest in, and debate of high quality broadcasting and recording was significant at this time - despite a rather significant war.

High quality recordings and magnetic pickups were available -

http://en.wikipedia.org/wiki/Decca_Records#ffrr

Recording and broadcasting often used very high quality ribbon microphones and amplifiers. And of course the UK and US not having tape recorders until after the war (captured from Germany and Japan), the distortion resulting from copied recordings was absent.

AM broadcasts were often very wide bandwidth and during the day were apparently very good. Leak, Quad and others produced high quality AM tuners. Hobbyists also built high performance receivers -

http://mike.wepoco.com/Home/wireless-world/1936-monodial-ac-super

Some also used tuners for the FM TV audio - where is was available.

Something that was known then, and sometimes seems to be forgotten today is that how an amplifier behaves between 100Hz and 10kHz is crucial. The very low and very high frequencies add to the sensation but if you don't get the range that the human ear is really best at - delivered with the highest fidelity (humans tend not to be able to detect less than a couple of percent of THD) then give up!

[Phil Allison[_3_]]

"mike s"

I have copies of just about every Wireless World magazine from 1934 to 1952.
It's quite apparent that there was a great deal of interest in, and debate
of high quality broadcasting and recording was significant at this time -
despite a rather significant war.

High quality recordings and magnetic pickups were available -

http://en.wikipedia.org/wiki/Decca_Records#ffrr


The " ffrr " is an ancestor of the Decca London stereo pickup.

A real groove straightener if I ever came across one.


> Recording and broadcasting often used very high quality ribbon microphones
> and amplifiers.

** Absolutely true.

Audio pros had sound quality available only dreamt of by the great unwashed.


> AM broadcasts were often very wide bandwidth and during the day were
> apparently very good.
> Leak, Quad and others produced high quality AM tuners.


** AM tuners from Quad et alia were of pretty narrow bandwidth and rather
high THD - but well suited to the very crowded AM bands in the UK and
Europe.

The only place where AM radio approached hi-fi quality was here in
stralia - where the government broadcaster ( the ABC) was very quality
conscious and co-channel transmitters were sited many hundreds of miles
apart.

I still own an example of the best AM tuner ever made available here - an
Audiosound AM100.

15kHz audio bandwidth, less than 1% THD at full modulation and a loop
antenna to virtually eliminate noise and interference. All valve - of
course.

One 6N8, one 6AN7 and one germanium diode.



.... Phil

[Patrick Turner]

On Jun 11, 10:00*pm, "Phil Allison" > wrote:
> "mike s"
>
> I have copies of just about every Wireless World magazine from 1934 to 1952.
> It's quite apparent that there was a great deal of interest in, and debate
> of high quality broadcasting and recording was significant at this time -
> despite a rather significant war.

People forget that Wireless World gave people of the world a wonderful
read about electronics from 1917 onwards. Just about every idea worth
understanding got a mention, and the letters sections gave dissenters
a voice and message worth reading.

snip 4 brevity,

> > AM broadcasts were often very wide bandwidth and during the day were
> > apparently very good.
> > *Leak, Quad and others *produced high quality AM tuners.
>
> ** AM tuners from Quad et alia were of pretty narrow bandwidth and rather
> high THD *- * but well suited to the very crowded AM bands in the UK and
> Europe.
>
> The only place where AM radio approached hi-fi quality was here in
> stralia * - *where the government broadcaster ( the ABC) was very quality
> conscious and co-channel transmitters were sited many hundreds of miles
> apart.

I have Quad AM tuner with SW bands. Its not a bad sounding unit. It
has switchable selectivity for MW broadcast bands done by switching in
a few turns of a tertiary winding on IF1, thereby giving double peaked
IF response while not changing skirt selectivity so the AF response
widens, and stations within 40kHz are well rejected. The trick is in
RDH4. The trick not in RDH4 is that you can mount one IFT coil and
tuning slug on a 10mm slide, to bring the coils together. Halicrafter
used 3 IFTs with variable coupling to vary the Q. In my AM tuner I
have such a slide I made to do similar. So hence AF is -3dB at 10kHz,
good enough for Oz widest broadcasts.
>
> I still own an example of the best AM tuner ever made available here - an
> Audiosound AM100.
>
> 15kHz audio bandwidth, less than 1% THD at full modulation and a loop
> antenna to virtually eliminate noise and interference. All valve *- *of
> course.
>
> One 6N8, one 6AN7 and one germanium diode.

Not a bad combo. have you tried 3 ge diodes in series? You'd be
surprised what happens.

I routinely replace original input RF transformers in old radios with
a ferrite rod antenna. One can still buy good long rods. The trick is
to use just the right number of turns to allow some rod movement to
vary inductance for the bottom of MW band, then also have just the
right inductance so that the trim cap on the tuning gang can be
altered to tune the top of the MW band while also allowing the right
tuning in the middle so that you get good TRACKING - very important.
The leads to the rod coil should be short, and a shielded coax cable
should be used. The coil should be wrapped with a couple of mm of low
dielectric constant insulation and a grounded copper foil shield
should be wrapped around after without forming a shorted turn so that
nearly all electrostatic RF input is denied, and the coil only reacts
to magnetic portion of RF, therefore not reacting to myriad
interferences from compact fluorescent lamp globes and other muck
which breaks all the laws about emitting interferences.

Not a bad idea to have a sharp cut off IF amp tube which generates AVC
voltage from its anode signal and then this is applied to an input RF
amp and partially to 6AN7 F converter. This way the IF amp remains
more linear, which it needs to be because that's where the greatest
amplification occurs. Taking the AVc off the IF amp anode via 33pF and
diodes etc is better because there is less sibilance during tuning,
although alinging IFTs can be more tricky.

Some say using 2MHz IFTs are better than 455kHz for MW because BW is
wider for a given Q, but maybe 3 IFTs are needed, not sure, have not
tried that trick, The oscillator must altered to suit as well.

>
> ... *Phil