Help identify a vintage amplifier

Good day everyone,

An unidentified amplifier came into my possession recently.

Accompanying this specific amp were two units, which I believe to be the W-3AM Williamson Amplifier with its power supply and also a Quad radio tuner along side a Quad 22 control unit.
First I thought they are related by the brand, manufacturer or maybe year of production.

However, further search has become somewhat frustrating as no plate, label or model number is to be found. I could only determine some of the parts suppliers: Clix Ediswan, Belling Lee L 720s, Bulgin English Make and R.F. Gilson LTD for the transformer.

The circuitry includes Hunt's capacitors and TCC electrolytic while their arrangement got me wondering about Leak's amplifiers – see attached photos at - http://jpegbay.com/gallery/004331028-1.html#1 . At this point, before starting to map out the circuit itself without any knowledge in electricity, I decided to turn to professionals.

Thus I ask for your help in classifying this equipment.


Many thanks,

Yair

 

Looks like it might have come off of a music instrument amplifier.

 

It has the look and feel of a homebrew built on Mullard or GEC plans in the UK : it has the characteristic Bulgin mains plug and is laid out just as recommended in the GEC books (Millett has it) or Mullard's book that was reprinted by OCSL in the nineties.

 

The W3Am was a US Heathkit product.

http://www.mcmlv.org/Archive/HiFi/HeathkitW3AM.pdf

DTN Williamson was an electrical engineer and author in Britain who published his design in the UK publication Wireless World in the late 1940s. It quickly spread to the US, to Continental Europe, and everywhere else, even in Russia people built them. He was not in the manufacturing business and "Williamson" was not a brand of amplifier. many manufacturers made "Williamson Type" or "Style" amplifiers but none were exactly to the Williamson specification.

The Williamson was the first popularly published and documented true high fidelity domestic audio amplifier in the open literature. Nonetheless, even by 1955 it was widely recognized to not be all that great from a stability standpoint. The unnecessary cathode follower drivers are much of the problem.

In the US, the original "horse's mouth" document was not well distributed outside of New York, and most Williamsons were built per a series in Audio Engineering magazine by Sarser and Sprinkle called "The Musicians Amplifier". Sarser was a violinist with the NBC Orchestra under Toscannini (sp?) which was an exceptionally prestigious billet, so this was a Big Deal. Sarser preferred Peerless transformers and so used one that had the ability to have its primary seriesed or paralleled for 2.5K or 10K ohms to 16/8/4 voice coil out. This gave a pair of center taps on each half primary which could be used to implement ultralinear screen grid connections even though it was not originally intended for that purpose. So in the US, people often called any ultralinear amplifier a "Williamson" even though the original Williamson used triode connection and in fact DTN Williamson disapproved of and wrote in opposition to ultralinear circuits.

 

I think this is a UK home built amplifier built according to the Mullard plans. Appears to have been a very carefully built amplifier. And construction is neat. That circuit was well designed and sounded great.

 

It definitely looks like an English amplifier made up from Mullard plans. However, I'm not sure that it's a homebrew. The construction details are similar to PYE amplifiers of the late 1950's. I think it's a pull from a PYE console.

 

PYE did use the Mullard circuitry. Maybe a Pye console pull or even a Mozart.

 

Thank you for your contribution so far.

Am I to understand this is not a specific model ?
Where can one find the relevant material for these Mullard or PYE designs ?

It is indeed possible the owner, who operated an electronics repair lab, ordered a kit of some sort for assembly.
The chassis has a sticker indicating payment of the "luxury" tax, levied during 1954 till mid 60's in Israel.

 

You want the Mullard book:

http://basaudio.net/blog/wp-content...164-Mullard-Circuits-for-Audio-Amplifiers.pdf

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

http://www.amazon.com/Mullard-Tube-Circuits-Audio-Amplifiers/dp/1882580036

 

Yes, the Mullard books on audio amplifier circuits and following schematics with a bit of knowledge will tell you what you need to know.