Radford Williamson amplifier

[TonyDuell]

Sorting out some stuff here I came across a valve amplifier (that I knew I had...). The nameplate says it's a Williamson Amplifier made by Radford Electronics.

Now I have the Williamson booklet and I assume it basically follows that circuit, so I should be able to get it working. But can anyone tell me a little about the history of it, the approximate date, etc. The only info I can find on the web was one that sold on Ebay some time back. It was serial number 117. Did the serial numbers start from 1, or some higher number?

[trobbins]

Some photos would be great to help others appreciate where to advise you.

Have you restored that type of equipment before?

[Edward Huggins]

This sounds very engaging - when you add Radford to Williamson you have a real find there....

[RojDW48]

Arthurs Radford and Bailey's amp designs were (like most) a development of Williamson's work but I have never seen a 'Radford Williamson'. This article is informative. http://www.audiomisc.co.uk/HFN/Radford/revisited.html

[TonyDuell]

I can take some photos of my unit, but if you go a Google image search for 'Radford Williamson Amplifier' you will find some pictures from a completed E-bay sale which (apart from the serial number) are identical to my unit.

I've never actually restored a Williamson before, but I've worked on valve amplifiers (and on plenty of other things) so I have a good idea what will be involved. I will ask if I have problems... No I certainly don't intend to connect it to the mains and speaker, switch on and hope!

I believe it pre-dates the well-known MA and SA series from Radford. I would like to know more about the history, the dates they were made, about how many were made, etc

[Diabolical Artificer]

Do you have the schematic Tony? As you know there were several iteration's of the Williamson design with changes to the OP valves and others.

Sounds like you have a rare bit of British hifi history there.

Andy.

[TonyDuell]

I have no specific information on the Radford Williamson. I do have the little booklet on how to make the Williamson amplifier which of course includes circuits. Said booklet is a later edition giving at least 2 versions.

I thought all Willamsons had triode-connected KT66s in the output stage, but that the earlier stages could either be double triodes or twice as many single triodes (L63's?)

Given the booklet I have, and the actual unit, it would not be too hard for me to trace out the circuit. It's simple compared to most of the things I work on.

[Diabolical Artificer]

One circuit I've seen uses 807's and then there were quite a few Williamson kits and wotnot made by tfmr manufacturer's like Acroasound and Edcor. I saw an interesting video here - https://www.youtube.com/watch?v=452FvupRIGw the other day about early hi fidelity valve amps and about their flaws. He also covers the Williamson design in detail. In the video he says the Williamson design was prone to HF oscillation, or at least the kits were.

Here's a link to the ebay amp Tony mentions - http://www.ebay.com/itm/Radford-039-...6551456?_ul=BO

A.

[thermionic]

Hi Tony.

According to information I have, then your Radford/Williamson amp was produced during 1954 -1955. Power output, 15 Watts, 5 Hz - 300kHz (?). +- 2dB. Harmonic distortion 0.1 per cent. Original price £32.10s.0d. 'A high quality amplifier based on the MK 11 (1949) version of the 1947 Williamson Circuit.'

Information above comes from the excellent 'Audio Audio' book by Jonathan Hill & John Howes. Recommended!

Anyway , I hope this will help a little.

SimonT

[Radio Wrangler]

Very interesting. Radford started as a transformer designer/manufacturer and this makes it look like his hifi products started with a published design.

The Australia pictures show it has Radford's signature big handles protecting the valves, but they also seem to show two holes in the chassis, about octal holder size.

Notice that the output transformer label makes a point of how many sections the output winding is divided into.

Anyone with one of these is going to find it rather expensive to get a second one for stereo.

David

[TonyDuell]

Thanks for the comments... My Williamson booklet is the 1949 version (that is it contains the original and then the Mk2 circuit) so it looks like I have something close to the circuit diagram. Said book also mentions the use of 807s in the output stage (I think for American readers who might have had problems getting KT66s).

Yes it has the large handles on the chassis.

As for getting a second one, I was given it years ago because the owner thought he would never get a stereo pair. At the same time he gave me a box of 'junk' which happened to include (amongst other things) a couple of KT66s and a Williamson output transformer. So while not an indentical pair, I think I could make up another Williamson Mk2.

There are 2 other things I would be interested to learn. One is roughly how many Radford Williamsons were made. The other is whether the serial number started a 1 (Is the one that was on E-bay the 117th one made or what?)

[trobbins]

Tony, I haven't come across that Radford Williamson, or seen a Williamson output transformer made in that style.

The OT is certainly interesting with its primary windings taken out through the outer insulation (very practical for a transformer with top mounted terminals), and the 'electric bolt' markings.

Anyone seen anything similar to that OT, or the power transformer and choke styles?

There may be date codes on the parts under the chassis, or even some of the valves may be original.

What was the other Williamson output transformer you have?

If you're keen on Williamson related literature, I have a compendium at http://dalmura.com.au/projects/Williamson.php

Ciao, Tim

PS. I'll ask John Murt who he sold the ebay Radford to - I've got some other amps through him over the years.

[RojDW48]

Certainly is going back a bit - it pre-dates the Radford factory at Ashton Gate. The seller reckons the txs were Partridge or Pameko - surely more likely their own (?) that's mostly what they did back then.

[PJL]

The ebay example shows extra cutouts for the single triode arrangement. Has it been modified? The valve sockets are bolted to the chassis too so maybe it was supplied in kit form.

[stevehertz]

Most equipment serial numbers start with 'large number' rather than at '1'. Although maybe '001' sometimes. In this case - so far - we just do not know what number they started with. I wouldn't be surprised if they started at '100' and the Aussie one is the 17th amp made. Tony, you don't say what number is on yours?

[TonyDuell]

I've looked at mine again. It has double triodes in the early stages, and no extra holes in the chassis. It looks like a capacitor has been replaced, the wiring to it is not tidy. But I will look into that.

As for the serial number, mine is 101 (!). So possibly a very early one.

The output transformer on mine is like the one in the E-bay listing. As with most original Williamson transformers, it has 8 secondaries that you could wire in series or parallel to select the output impedance. You also had to change a resistor in the negative feedback circuit, that's the reason for the 'feedback resistor' tags on top of the transformer. All changes were made to tags there.

I assumed the transformers were Radford's own as that is what they were known for at the time.

[Radio Wrangler]

Some companies started serial numbers not at 1, so as to not have customers thinking they'd bought a prototype or very early example.

What if they'd started from 100? !

David

[stevehertz]

You mean like I explained in post 15?

[Radio Wrangler]

Exactly! It was the traditional start at HP, for example, but I don't suppose we'll ever know because those things seem very rare and the chances of ever collecting enough serial numbers to deduce the start point are very slim.

David

[trobbins]

The only time reference I can locate for Radford Electronics at Newfoundland Rd, Bristol is July 1954 (in WW).
The earliest I can see Radford Electronics at Ashton Grove, Bristol is 1960. All the Labpack front panels show Ashton Grove.

Pity they didn't advertise much in the 1950's. Finding when they were at Newfoundland Rd would be informative for dating.

The lack of other 1950's Radford equipment makes it difficult to know if the distinctive bell-end feet design was from Radford.

The chassis / handle style is certainly distinctive of 1960's Radford equipment.