Williamson amplifier

[Alan Stepney]

I have always thought that the Williamson was THE best audio amplifier.

That is despite having owned, and worked on, almost everything from Quad, Leak, and products from many other manufacturers.

I am contemplating making a new pair of Williamsons.
The key component is the output transformer.

In their heyday, Partridge were reckoned to be the best, (or one of the best) makers of these.
Partidge still exist, and can still supply transformers to the original specification.

However, looking round the internet, there are some sites where people claim that the original design was either not as good as it might have been, or can be improved using modern materials.

Question?

If you were planning to build a pair of Williamsons, would you.
1) Ask Partridge for transformers to the original specification?
2) ask Partridge for transformers for that task and ask if they have, or can, update the design?
3) Contact one of the other makers who advertise "transformers to their own improved design"?
4) Look around for an old, original pair of OP Tx's?
5)) anything else?

I expect that a new matching set of OP Tx, mains Tx, chokes etc, from Partridge, will cost an arm and a leg, and as I will need to duplicate it for stereo, 'nuff sed!

Comments and suggestions welcomed.

[Aub]

Alan,

An interesting and thought provoking set of questions.

I didn't realise that Partridge still exist. I'll do a Google on them in a moment. I would imagine that it would be difficult for Partrige to make them exactly to the original design as, i suspect, the materials are so much better now ( unless they deliberatley used older materials ) They would certainly cost a lot, probably around £100 for each O/P transformer and more for the mains transformer. Then there's the chokes, and that's probably without VAT.

You could ask for a quote from Partridge and, perhaps, Sowter, and compare them. I know that Sowter make their own "optimised" design for the quad amps, so they would probably have something similar for the Williamson.

The Williamson's are triode connected designes, which is probably what makes them sound so nice.

All the best.

Aub

[GrimJosef]

Sowter have an on-line price list. The prices for Williamson transformers are:

Output £180.42
Mains £142.82
Choke £43.04

I believe VAT has to be added on top.

The OPTx weighs 7kg and looks jolly clever which, I guess, is why it costs what it does. Then again Morgan Jones says in his "Valve Amplifiers" book that it did need to be "very closely specified".

Cheers,

GJ

[mastermanx2001]

I have a Willamson amplifier that was made in the Rogers factory (a long time ago). It does use Partridge transformers and PX25 output valves. This is probably the best amplifier that I have ever heard. The next best amp that I have heard is Radford STA25 with JJ KT77 output valves (using this at the moment). I do like the Quad II as well. All of these I prefer to any transistor amp that I have owned, which includes transistor Quad and Radford models.

[Alan Stepney]

I still have one Williamson, that my father made when the design first appeared, and later, modified in line with the changes in, I think, 1952 or 3.
It was one of a pair, but unfortunately the second one was disposed of long ago.

I have been told that the Partridge Tx+ choke package, costs well over £600, but how accurate or recent, that price is, and whether it is with or without VAT, I know not.

I did see the Sowter prices, but, how good are they compared to the original?
They say "improved", but I am a born sceptic!

One thing is for sure, buying two sets of wound components is going to be expensive, and buying multiple sets to compare them, would do serious harm to my wallet!

One Dutch enthusiast, (see http://www.xs4all.nl/~ideas/amps/) claims to have designed a better OP Tx, and is willing to sell the design, but at a price.

I am sure everyone can appreciate my wanting as much information, and opinions, before spending that much on, basically, a whim.

Partridge are now T & R, http://www.transformers.co.uk/index.asp?pgid=27


The one advantage I do have is several new M.O KT66's, thus saving a fortune at todays prices.

[Ed_Dinning]

Hi Alan, I have wound several of these in my time, both old types and modern ones.
If modern lams are used in Unisil material they will in theory have less distortion as they approach saturation as the curve is more gradual than in Stalloy.
Some of the modern transformers have earthed screen over each of the secondary windinf sections. This is so the stray capacitance (inherent in multi-section transformers) is tp earth, not across the transformer and possibly upsetting the feedback circuits.

Let me know if you need assistance with the re-wind; I have the Wireless World data book and it gives details of the sectionalisation of the Partridge transformers.

Ed

[mastermanx2001]

There is a Williamson on e bay at the moment, may well have Partridge transformers.

[evingar]

There is also a Williamson on there that explicitly states it has Partridge transformers :-
http://cgi.ebay.co.uk/partridge-will...QQcmdZViewItem

Lots of dosh though

[mastermanx2001]

Some good info here, including info on transformers:

http://www.dc-daylight.ltd.uk/Valve-...gust-1949.html

http://www.dc-daylight.ltd.uk/Valve-...-May-1947.html

[Alan Stepney]

Thanks for all the comments.

If I went for that amp on Ebay I would only want the Tx's, and that would make them more expensive than new ones. I think!

I guess the next step is to talk to Partridges to see what they say. Oh, and save some pennies!

[mastermanx2001]

I have a feeling that the expensive one on e bay is the same unit as appeared earlier on e bay incorporated into a console with a Dulci tuner and record deck. It went for less than £50, the only thing that stopped me buying it was it was for collection only and it was too far away, missed bargain?

I am very impressed with my Radford STA25 and it seem even better since fitting JJ KT77 valves. These are incredible value, I think I paid under £50 per set of four including air mail from the States. I know that you have some new GEC KT66s, but I would be a bit scared to use these every day.

I wonder if JJ KT77 could be used in a Williamson design.

I run the Radford STA25 all day and dont worry about valve replacements and cost now.

[Ed_Dinning]

Hi Gents, a quick look at the valve data shows thatthe'77 has a higher heater current, and a top anode voltage of 600 as opposed to 500 for the '66. Neg grid voltages are lower for the '77 (about1/2) but anode and screen currents are similar. Drive levels are similar as is the R load and output powers. Note that base connections are different.
It could be worth a try if you can easily adjust the bias. The '77 is designated as an o/p valve, not a stabiliser, so let us know what it sounds like.

Ed

[camtechman]

I can't add anything to the topic but whilst having a clearout, after my recent move, I've come across this book amongst my late Father's bits & pieces.

I presume this book relates to the amplifier you are discussing?:

[phase_splitter]

Sowter TX are excellent; I've used them several times.
Transformers and Rectifiers are somewhat awkward to deal with; quoting long lead times (3-4 months)
I presume they fit the audio TXs into production gaps of their bread and butter work; (extremely) large mains TXs.
Also might be worth talking to Majestic, who I can also recommend.
www.transformers.uk.com

Nothing sounds nicer than a PPKT66 amp; IMO.

[Alan Stepney]

Camtechman, that is indeed the booklet.
I'm not sure about editions, but it should have the modified Williamson, and if so, that is the one (2) I will be building.

Phase Splitter,
Thanks for the info re Majestic.

[kalee20]

Phase Splitter, thanks from me also!

[mastermanx2001]

Just in case anyone is interested here are some pictures of a Willamson that was made in the Rogers factory, in the early days, probably by my uncle. It has had a very hard long life and was run about two years ago, still sounds more than excellent. Excuse the poor photos and vintage dust.

There is a pre amp that goes with this, I will have to take some photos if anyone wants to se it.

[Septimus]

Hello,
This will be my first post on this site.

A Williamson, mono, amplifier was given to me by a now deceased relative a few years ago. He built the thing in 1951 using the plans camtechman posted. (which I also have but in not as good condition)

Occasionally I turn it on and play a old piece of vinyl. (must use solid state preamp)
It has original Partridge transformers in it, oil filled caps etc.

I must use a contemporary speaker, but have considered building something more in keeping with the amplifier's age. Any ideas??

[Sean Williams]

Voight Horn?

Ive seen one homebrew one, and it was HUGE, sadly very woodwormy, but I inderstand they are good speakers if designed and build well....

[dave walsh]

Septimus, this is even before my time but for strict authenticity, you probaly need a 10" 15 ohm Wharfedale Speaker in a sand filled corner enclosure. Probaly a GA Briggs [Yorkshire] type design. [Possibly built in brick].
One 1960's Practical Wireless cabinet used poured concrete panels!
This is all pre "book shelf" reproducers or active units, of course.
A BBC Transmission Speaker [or equivalent] might be an alternative.
Seems to be a lot of info on the net. Dave W