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Old 16th Jan 2022, 9:46 am   #1
Phil-G0SXY
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Default Williamson output transformer identification

Before Christmas my eldest brother was having a bit of a clear out and one of the items was our Dad's old Williamson amp which he built in the 1950s, it's the 1949 circuit using 4 x L63 triodes with the alternative 3.6Ω secondary windings on the output.

None the transformers or chokes had any markings on them but I expect they may be military surplus, C9 (8uF 600V) does has 10C/13271 stamped on it.

Does anyone recognise this style of transformer?
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Old 16th Jan 2022, 10:38 am   #2
joebog1
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Default Re: Williamson output transformer identification

Those transformers look to be made to the origional specifications. A "true" Williamson transformer is wound with two identical bobbins. We dont do it that way anymore, but Williamson worked out the most ideal setup with what was available at the time.
They are DEFINATLY NOT military surplus !!!. Those would have cost your father some considerable quid !!!.
I may be wrong, BUT I would have those checked by somebody that knows his mustard !!
To me they look exactly as Williamson designed.

They are worth a LOT of money in Japan and China.
DO NOT be conned out of them.

Joe
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Old 16th Jan 2022, 10:45 am   #3
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Default Re: Williamson output transformer identification

The transformers would not be ex-military with "Williamson" engraved on the terminal panel.

Around that period there was an immense amount of government surplus components on the market. WWII stopped rather abruptly in view of the vast amount of material in production pipelines which went for disposal for any price they thought they could get for it.

If the transformers were specially wound, it's likely that the laminations, fittings papers and even wires were types used in the war. It's a period when a lot was happening.

David
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Old 16th Jan 2022, 10:50 am   #4
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Default Re: Williamson output transformer identification

Williamson's original article included the complete instructions for winding the output transformer. The idea was that home constructors could make their own. As such there are lots of different versions out there, including both extremely good ones from commercial winders and (let's be generous) 'basic' ones produced by beginners. The fact that the terminal plate has text engraved in it tends to suggest this transformer isn't homebrewed. But the lack of any indication of which terminal is which is a bit unusual. I wonder if it might have been a kit unit ?

Cheers,

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Old 16th Jan 2022, 11:20 am   #5
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Default Re: Williamson output transformer identification

The panel looks similar but not identical to mine, which is a Partridge. Mine doesn`t say Williamson and has the panel on top, rather than at the side.

My amplifier, which was built by my uncle in the early fifties was originally the PX4 version but an accident involving a leaky roof meant I needed a new mains transformer and the easily available replacement only had 6.5 volt heater windings so I converted it for KT66s.

It was last used as a calibration amplifier and is currently in storage, I intend to rebuild it one day.....
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Old 16th Jan 2022, 11:31 am   #6
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Default Re: Williamson output transformer identification

Hi David,
My ref to military surplus was for the mains transformer and chokes rather than the output one, sorry for any confusion, the mains unit has 425-0-425, 5V CT, 2 x 6.3V CT and an earth/shielding lead. The chokes (on my LCR meter) read 50H & 20H so larger than specified.

Hi GJ,
Never thought about a kit version, I did quickly scan through online copies of WW from that era looking for pictures but didn't find any so i may take a closer look at the text only advertisements. The only faceplate i have seen "similar" to this one is from the Radford Williamson amp.
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Old 16th Jan 2022, 11:55 am   #7
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Default Re: Williamson output transformer identification

Quote:
Originally Posted by joebog1 View Post
Those transformers look to be made to the origional specifications. A "true" Williamson transformer is wound with two identical bobbins. We dont do it that way anymore, but Williamson worked out the most ideal setup with what was available at the time.
They are DEFINATLY NOT military surplus !!!. Those would have cost your father some considerable quid !!!.
I may be wrong, BUT I would have those checked by somebody that knows his mustard !!
To me they look exactly as Williamson designed.

They are worth a LOT of money in Japan and China.
DO NOT be conned out of them.

Joe
Hi Joe,
I was wondering why this had 2 bobbins as almost all the pictures I have seen of others only have 1.
On first glance i can see from the external wires that the windings are pri/sec/pri/sec etc, the transformer is all ok and still works (i only have the one) before i dismantled the chassis and parts for cleaning and refurb i did quickly check it over, replaced a few components, powered it up slowly and heard nothing on the speaker, thought it was broken until i put my finger on the input and a loud hum appeared!
I quickly ran a Bode plot on it and considering the age and lots of poor solder joints (sorry Dad!) i think it did very well.
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Old 16th Jan 2022, 11:59 am   #8
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Default Re: Williamson output transformer identification

There were quite a few companies advertising that they made or sold transformers for the Williamson amp, eg. Ashworth from Bradford and , Coulphone Radio (WW Jan 1950), or sold kits.

A photo or two of the power transformer and chokes may help, as they were likely made by the same company.

Partridge certainly used holes in the side walls of their former to pass links or wires.

The transformer's worth is imho suspect until some testing confirms it has acceptable resonances and inductance, given that some commercial models I have tested of that era are not great performers. If the amp is still in fair condition then it would be worthwhile restoring if you were so inclined - but that should include a stability assessment as not all such amplifiers performed as anticipated.

PS, I just saw the above post with bode plot. You will need to go well above 100kHz and well below 10Hz for stability assessment, or do some squarewave tests for HF performance. The first resonance at 50-70kHz is nominal.
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Old 16th Jan 2022, 12:29 pm   #9
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Default Re: Williamson output transformer identification

Hi Tim,
Here is a link to my Amazon album of the amp https://www.amazon.co.uk/photos/shar...DbIwuv3FWGUYK3

As it was my Dad that built it and i have fond memories of using it in my youth it will be rebuilt just to keep it in good working order and looking nicer than its current condition!
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Old 16th Jan 2022, 12:54 pm   #10
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Default Re: Williamson output transformer identification

That does seem typical of a 1950's diy build Well done for not casting it aside.

Do any of the valves and the can cap have date codes? That may clarify when in the 1950's it was constructed.

If squarewave response shows nothing too dominant then you may be able to back off the input stage step filter if you can confirm stable operation for a range of typically bad loads.

Did you know what 15 ohm speaker your dad used? The LF peak may be substantial and around a few Hz, so perhaps be mindful of avoiding signal excitation in that area.
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Old 16th Jan 2022, 1:22 pm   #11
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Default Re: Williamson output transformer identification

I do not think they are Partridge they do not look high enough in quality, they are not Woden either both would have marked their transformers with the appropriate code.

I had a Williamson Partridge transformer I sold it, I two Williamsons but my landlord lost one in a move of a few hundred metres. That means i had two with Woden WOT 25 (I think that is the code) and a spare Woden WOT 25 transformer.

My money is Elstone or someone like that....
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Old 16th Jan 2022, 1:40 pm   #12
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Default Re: Williamson output transformer identification

The output transformer does not appear to be by a mainstream manufacturer of the time (well not from the accumulation of photos of various brit makers I've come across so far) - maybe someone has seen that type of bell-end as used in the choke and power transformer.
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Old 16th Jan 2022, 10:29 pm   #13
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Default Re: Williamson output transformer identification

I notice in your photoes what appears to be a BIG paper in oil main filter cap. If that is so I would NOT touch those two exposed terminals on top!!!. I would suggest you won't be alive to listen to them.

Just a gentle warning.

Joe
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Old 16th Jan 2022, 11:52 pm   #14
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Default Re: Williamson output transformer identification

Elstone transformers often painted their products green.
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Old 17th Jan 2022, 12:28 am   #15
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Default Re: Williamson output transformer identification

It looks too dark and shiny for Elstone green.

https://vintage-radio.net/forum/showthread.php?t=46598
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Old 17th Jan 2022, 7:56 am   #16
Phil-G0SXY
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Default Re: Williamson output transformer identification

Quote:
Originally Posted by trobbins View Post
That does seem typical of a 1950's diy build Well done for not casting it aside.

Do any of the valves and the can cap have date codes? That may clarify when in the 1950's it was constructed.

If squarewave response shows nothing too dominant then you may be able to back off the input stage step filter if you can confirm stable operation for a range of typically bad loads.

Did you know what 15 ohm speaker your dad used? The LF peak may be substantial and around a few Hz, so perhaps be mindful of avoiding signal excitation in that area.
Once it is rebuilt I'll do some more frequency response testing, with regards to the speakers, I had to ask my brother about those and his reply was...

2 off 12" 16ohm base drivers wired in parallel, in series with a large choke.
1 off 5"x 7" 16ohm mid frequency driver with series capacitor. Paper cone with enclosed back.
1 off 3" 16ohm tweeter with series capacitor. Paper cone, enclosed back.
All drivers made by Elac. (Electro Acoustic Industries Ltd UK)
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Old 17th Jan 2022, 8:02 am   #17
Phil-G0SXY
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Default Re: Williamson output transformer identification

Quote:
Originally Posted by joebog1 View Post
I notice in your photoes what appears to be a BIG paper in oil main filter cap. If that is so I would NOT touch those two exposed terminals on top!!!. I would suggest you won't be alive to listen to them.

Just a gentle warning.

Joe
HaHa yes exposed HV terminals and on the back 2 exposed fuse holders for the live and neutral mains supply and NO earth connection - These are one of the reasons it is being rebuilt!
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Old 17th Jan 2022, 8:27 am   #18
Phil-G0SXY
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Default Re: Williamson output transformer identification

Quote:
Originally Posted by Silicon View Post
Elstone transformers often painted their products green.

This one, the mains transformer and chokes were originally painted grey, the green paint was put on afterwards.
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Old 17th Jan 2022, 11:35 am   #19
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Default Re: Williamson output transformer identification

Interesting that the woofer setup is presenting a nominal 8 ohm, given the output transformer secondary appears to be wired for 15 ohm.
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