Williamson Amplifier

spongebob
19th February 2009, 11:59
Williamson Amplifier;

I post this in a hope that some of you radio men may confirm my memories about this one time so called wonder amplifier.


After the war when musical recordings became readily available again Dad started to collect Classical 78 rpm records which meant buying a new electric turn table and playing them through the old console radio but as the old steel needles were still the norm, just before the advent of sapphire tips, he went ‘up-market’ by using fibre needles to avoid damage to the new recordings. These needles were in fact made from slithers of bamboo and were shaped and sharpened after every play by fitting them into a small chuck and stropping them in a machine rather like the old ‘Rolls’ Razor system.
This produced scratch free sound but the old radio was not up to the quality of amplification that he wanted so the next step was a ‘Williamson’ amplifier. This post war design amplifier/receiver was apparently acknowledged as one of the world’s best in its time, a huge contraption by today’s standards and boasting about 18 valves in its circuitry. An order was duly placed at cost of perhaps thousands of dollars by today’s values and when it arrived as a bare aluminium chassis and protruding bunch of valves it was quickly placed in an old apple case as a temporary measure to protect children and others from heat and shock and fired up. It was too powerful for the small speaker in the old radio so the next purchase was a 12 inch iron frame base speaker at further great expense.
The assembly certainly produced flawless musical reproduction by the standards of the day and once this was achieved the amplifier was sat in its box on the sideboard, the turntable in its temporary housing next to it and the big speaker perched on a temporary shelf in the corner. There it remained until it was obsolete or another development took his fancy

Bob

mikeg
19th February 2009, 13:18
Hi Bob,

I know the Williamson Amplifier quite well (being in the hi-fi trade for a number of years). It was indeed a high quality amplifier in it's day..and in fact still is if you care to build one with modern components -if you can get someone to wind the very specific and critical output transformer that is!
D.T.N Williamson worked for the M.O. Valve Company before moving on to the Ferranti Research Labs. He was clever by getting rid of the coupling capacitors or condensors then :) in the initial stages to keep the phase shift at low frequencies minimal by designing the critical first two stages as one.
The anode of V1 at +100V was connected directly to the control grid of V2 but the cathode of V2 was at just over 100V, so what the grid 'sees' of course is in respect to its cathode. V2 acted as a cathode follower to one half of the phase splitter and the anode to other.
The quality of the OP Transformer was critical but there still are a number of firms around (like Sowter) if you want one 'bespoke' wound - but it'll cost!
The valves are all still available as are the reprints of the circuit, taken from 'Wireless World' of 1947 and 1949. In the August 1949's update, Williamson recommended using 6SN7s in the early stages instead of the earlier stated L63's. The output stages were triode connected KT66's or 6L6's.
I was very tempted to build one - but like many things it was the 'roundtoit' that stopped me.
Of course it will sound much better nowadays as we now have carbon film resistors which are less noisy plus better built and more reliable capacitors.
Its also another way of keeping you warm in the cold winter months.


Mike

PS I've just found a link to all the info you'll ever need to build one here : http://www.audioxpress.com/bksprods/products/cdaa2.htm

benjidog
19th February 2009, 19:48
Bob,

Your mention of "made to measure" transformers transported me back to my first job after leaving school. This was at the Post Office Research Station at Dollis Hill in NW London. There was an entire room full of people winding coils for the various transformers required in the equipment being developed. It was fascinating to watch and reminded me a bit of a mill full of weaving looms. Coils of wire of various gauges fed the winding machines - I think the copper wire was covered with some kind of enamel finish as insulation. There were counters to measure how many turns had been put on a coil - my memory is a bit hazy but I think there were a bit like the old fashioned mileometers we used to have on our bikes.

There are still a few wire coil devices in modern computer motherboards, but apart from mains transformers and special designs I would thing that this technology is pretty well obsolete now.

mikeg
19th February 2009, 20:41
Re my earlier posting - I've Just looked up Sowters and they do have transformers available for the Williamson. The output transformer plus the supply choke & mains transformer comes to approx £420, then you still need to buy the chassis, all the components including valves and valve bases...ouch!!

spongebob
20th February 2009, 07:26
Thanks for that mikeg and benjidog. It confirms my boyhood memory of the amplifier and sounds like my Dad was on the right track.
I don't think that I will try to make one, my best effort was a crystal set.

Bob