UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 12th Apr 2021, 11:20 am   #1
Bill
Pentode
 
Join Date: Dec 2005
Location: Denton, Manchester, UK.
Posts: 186
Default Williamson stereo pair, a good idea or not?

I have 3 Williamson o/p transformers, one Partridge WWFB/.95 and two Gardners OT736. I have in mind a project to build a pair of amplifiers to original design but using 807s instead of KT66. I have a 400-0-400, 300mA mains tx , would this be enough to supply both amps, using 2x CV378/5U4 with separate chokes and filtering? Apart from considerations of efficiency and weight(!) would these sound any better than the Leak Stereo 30+ that I currently listen to? Possibly a mad project, but I do have most of the serious parts for this.Also, what is the power rating for these O/P txs? The specs say 20w but they look more than capable of 100w?The primaries are 10k a to a. Thanks.
Bill is offline  
Old 12th Apr 2021, 11:45 am   #2
joebog1
Banned
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
Default Re: Williamson stereo pair, a good idea or not?

Well, you are correct in surmising that they are 100 watts plus, BUT its Hi-Fi!! after all its basically Williamson that coined the phrase " Hi-Fi " SOO the traffos are at best 20 watts. Williamson amps are "rated" at 15 watts RMS, which translates today as 250billion PMPO watts.

Williamson amps are HIGHLY desirable !!! VERY VERY desirable.

Actual output power will be very close to 15 watts RMS, but with the amps very hot, and with a downhill slope you may catch em out at about 18 watts before clipping, at 400 Hz, the test frequency at that time. NOT 1kHz as is now used. Construction of "true" Williamson output transformers is VERY complex, NOT efficient!, but very complex indeed.
There were in the origional design TWO bobbins, wound identically. One bobbin was the spun around and placed on the core "backwards" to the other. There were TEN primary windings on each core half.
If you want "phat" distortion for your guitar, FORGET it, it just doesnt happen. BUT, listen to real music, and you will see what I mean. Especially female vocals, ( probably the hardest sound to reproduce).

Just my three bobs worth,

Joe

with great respect!
joebog1 is offline  
Old 12th Apr 2021, 3:33 pm   #3
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Williamson stereo pair, a good idea or not?

The Gardners transformers were wound for the Williamson design and have 8 separate secondary windings. !5W will be more than loud enough... and it will sound much better than your Leak Stereo 30 and any other early transistor amp that uses capacitive speaker coupling.

I would be inclined to use new EL34B's (made in china) as they are pretty cheap, reasonably reliable, and will use the same connections as the KT66.

The power transformer should be OK for HT current but you do not mention the LT windings?
PJL is offline  
Old 12th Apr 2021, 3:48 pm   #4
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
Default Re: Williamson stereo pair, a good idea or not?

Quote:
Originally Posted by joebog1 View Post
Williamson amps are HIGHLY desirable !!! VERY VERY desirable.
Just out of curiousity, how 'desirable' would an original Radford Williamson amplifier, serial number 101, be?
TonyDuell is online now  
Old 12th Apr 2021, 4:30 pm   #5
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: Williamson stereo pair, a good idea or not?

Radford Williamson? Desirable enough that if you told some hifi fanatics you'd have to dump a bucket of iced water over them. They'll lose their interest once they get to thinking of the probability of finding another, and the cost if they did.

Transistor amps with output capacitors have a low frequency roll-off that can be avoided in DC output coupled designs. But then valve amps have a low frequency rolloff inherent in their output transformer. I'm not sure why one would be preferable to the other, though transformers have more imperfections than capacitors.

I wouldn't put the blame directly on the output capacitor per se, but transistor amp designers have learned a few things since the era of the Leak Stereo 30.... a few things which do actually matter.

If you subscribe to the "It's got to be valves" mindset then you reduce your choice. and the Williamson is a good valve amplifier. But if you have an open mind, there are also good transistor amplifiers.

Triodes, tetrodes, pentodes, beam tetrodes, bipolar transistors and field effect transistors ALL have limitations and foibles. A good designer can design a good audio amplifier around any of them. The art lies in doing designs which overcome or cover their problems. No one technology is necessarily superior to the others. But I'll take a good design over a bad one.

It's a doddle to look at an amplifier and say what technology of devices it uses. It's a lot harder to look and tell a good design from a bad one. So people put all the blame and plaudits on the type of device, not on the design it's used in.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 12th Apr 2021, 8:57 pm   #6
Bill
Pentode
 
Join Date: Dec 2005
Location: Denton, Manchester, UK.
Posts: 186
Default Re: Williamson stereo pair, a good idea or not?

Quote:
Originally Posted by PJL View Post
The power transformer should be OK for HT current but you do not mention the LT windings?
It has those as well! 5v 6a, 6.3 4.5a,6.3 10a. It's a big transformer but in any case I have two of them. I would be interested to know the make of them. Square oil filled can with rounded top corners, painted black with solder seal at the terminal end, glass insulated solder terminals, voltages etc printed in black, very heavy. I have no idea what equipment they came from , had them 50 years or so.
Bill is offline  
Old 12th Apr 2021, 9:47 pm   #7
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Williamson stereo pair, a good idea or not?

Hi Bill, probably Parmeko

Ed
Ed_Dinning is offline  
Old 12th Apr 2021, 10:21 pm   #8
joebog1
Banned
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
Default Re: Williamson stereo pair, a good idea or not?

To Tony, Read what David has written, then double it.
To PJL, EL34/6CA7, are not plugin replacements for KT66. 6CA7's are pentodes not beam tetrodes and as such does not have beam forming plates, but does have a supressor grid that must be connected. Its pin 8 BTW. Also if 6CA7's are used in triode mode as are the KT66's in Williamsons design, the screen resistor must be upped to 470 ohms. One reason my amplifier is being made is that I am using 5B/254 AKA CV428 which are plentiful and cheap, made in England, and a very close sub for a KT66 or an 807 which is what Williamson used. My experience with "modern" output valves is sad to say the least. If the thought of top caps with 450 odd volts on them is a bit scary, you can use 5B/255 AKA CV391 which is the same valve but has the plate connected to a base pin and no top cap.


Just my take on it.
Attached Thumbnails
Click image for larger version

Name:	adv-0510.jpg
Views:	140
Size:	102.8 KB
ID:	231645  
joebog1 is offline  
Old 12th Apr 2021, 10:34 pm   #9
TowerRadio
Hexode
 
Join Date: Mar 2008
Location: Bristol, UK.
Posts: 388
Default Re: Williamson stereo pair, a good idea or not?

A modified Williamson circuit using 807's is described in the Radio Designers Handbook,807's strapped as triodes.Les
TowerRadio is offline  
Old 13th Apr 2021, 7:50 am   #10
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,636
Default Re: Williamson stereo pair, a good idea or not?

I have in mind a project to build a pair of amplifiers to original design but using 807s instead of KT66. The only problem is 807's have a lower Vg2 max of 300v,but they can be run at higher voltage as long as Pdiss max is kept within limits. I agree, EL34's would be a good fit, Langrex do some good ones called Langrex Premium.

Your OPT's might drop into the Williamson circuit with no issues but you might need to do some testing and modifications.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 14th Apr 2021, 4:47 pm   #11
Wendymott
Octode
 
Wendymott's Avatar
 
Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,782
Default Re: Williamson stereo pair, a good idea or not?

Many years ago, as an apprentice TV engineer, our local garage owner had a Mono Williamson amp..... no idea what the preamp was..... The Output transformer became faulty. Obviously there was no direct replacement..... well not known to us anyway... "no ebay" then.... so a Gardners transformer was ordered and fitted. The owner got it back and the very next day it was back with us...... apparently he was a Hi Fi "nerd" and he was most dischuffed. We took out the Gardners, he scrapped the amp... gave it to me as it happens..and bought some Fisher or Radford or Leak...and became an Audiophool.......The valves were PX25's
__________________
Should get out more.

Regards
Wendy G8BZY
Wendymott is offline  
Old 1st Jun 2021, 5:13 am   #12
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 898
Default Re: Williamson stereo pair, a good idea or not?

The two OT736 would make an excellent stereo pair using a slightly modified Williamson circuit. You could pay for your retirement by then selling the WWFB to someone who just has one of those (like me) and hence make the world a bit more stereo symmetric for everyone.

How technical are you Bill, as it is in your interests imho to make the effort to not only prepare the amps technically, but also to test them adequately, to avoid the dismay that many had half a decade ago. There is a link below to a technical doc which may help if you had some technical queries.

The basic concerns of Williamson stability are fairly well known now, and the remedial tweaks to make them unconditionally stable have been known for half a decade but often not applied.

One advantage of your power transformer (and its huge heater current capability) is that you could use a quad output stage of triodes (such as 807) - Williamson prepared such a beast back when he was at Marconi. That can give you enough to push the OPTs, as it is mainly the valve distortion that dominates a standard Williamson as 15W is approached, plus a common stability tweak is to slightly roll-off the bass end which may then allow the OPT to not be the low end limiter at max power.

The other link below is to some recent testing I did on a WWFB, and it indicates that the OT736 may be a better performer than the OT735, especially if the OT735 needed a mixed parallel/series connections of secondaries to get to your speaker impedance, given that the OT736 best suits 4 or 16 ohm speakers. I haven't seen much on that Gardeners OPT (apart from their general catalog and a simple frequency plot for the 735) so if you come across anything then please post it.

https://dalmura.com.au/static/Willia...ign%20info.pdf
https://dalmura.com.au/static/Willia...asurements.pdf
trobbins is offline  
Old 1st Jun 2021, 11:01 am   #13
joebog1
Banned
 
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
Default Re: Williamson stereo pair, a good idea or not?

Thank you Tim for a superb explanation.
It is very nice to see true engineering still working.
I have saved the link to re-read as its a bit overwhelming.


Joe
joebog1 is offline  
Old 4th Jun 2021, 6:13 pm   #14
Jez1234
Banned
 
Join Date: Mar 2021
Location: Morpeth, Northumberland, UK.
Posts: 936
Default Re: Williamson stereo pair, a good idea or not?

The OP has a veritable holy grail of output transformers there! The lucky... ahem, so and so!

The Leak Stereo 30+ is a really poor amplifier and a Williamson amplifier is in a completely different league. We are comparing Man U with Accrington Stanley here!

As it happens my own latest power amp design uses capacitor coupling to speakers.. big capacitors and with AC NFB taken after the output cap. WHY? As an impoverished OMB I want to make it idiot proof as the last thing I want is someone abusing it and then trying to make some claim against me because it went DC and took out a woofer in their £25,000 "Acme WunderTone" speakers! The "target audience" of audiophools also seems to think there is an advantage sound wise so why not give 'em what they want...
Yes there are numerous other protection methods but not always 100% effective and can be troublesome in their own ways (dirty relay contacts after a few years etc).
Jez1234 is offline  
Old 7th Jun 2021, 6:44 pm   #15
johnyjf
Tetrode
 
Join Date: Apr 2013
Location: Reading, Berkshire, UK.
Posts: 54
Default Re: Williamson stereo pair, a good idea or not?

Over 2 decades ago I built pair of Willliamsons using GEC KT66s and Sowter Transformers, those were the days. They had a very clean sound, the proverbial valve sound (added warmth) was virtually absent. The FR was very good, they were still developing 10watts at 120KHz, power output didn't drop to zero at near to 200KHz if memory serves me well. They cost a fortune then but I made a small profit when I sold them, they weren't a living room amp and I didn't want to upset SWIMBO. Good luck with your project, you'll have a lot of fun but unless you construction standards are impeccable or your better half far more tolerant than mine I shouldn't count on putting them anywhere sociable.
__________________
Regards

Johnyjf
johnyjf is offline  
Old 8th Jun 2021, 1:24 pm   #16
Jez1234
Banned
 
Join Date: Mar 2021
Location: Morpeth, Northumberland, UK.
Posts: 936
Default Re: Williamson stereo pair, a good idea or not?

The OP will need some seriously good speakers and source to get the best from the Williamson amps of course.... If the Leak 30 Plus was used with typical Wharfedale Linton's or some such they ain't going to cut it!
Jez1234 is offline  
Old 8th Jun 2021, 1:29 pm   #17
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Williamson stereo pair, a good idea or not?

Quote:
Originally Posted by johnyjf View Post
... the proverbial valve sound (added warmth) was virtually absent ...
As someone once said "If your valve amp has 'the valve sound' what does that tell you ? It tells you that there's something wrong with it, that's what." .

Cheers,

GJ
__________________
http://www.ampregen.com
GrimJosef is offline  
Old 8th Jun 2021, 1:37 pm   #18
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: Williamson stereo pair, a good idea or not?

Quote:
Originally Posted by GrimJosef View Post
As someone once said "If your valve amp has 'the valve sound' what does that tell you ? It tells you that there's something wrong with it, that's what." .
Love it! Some people just forget that they're trying to listen to the music

Ignore the wine, Taste the glass!

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 14th Jun 2021, 8:36 pm   #19
Bill
Pentode
 
Join Date: Dec 2005
Location: Denton, Manchester, UK.
Posts: 186
Default Re: Williamson stereo pair, a good idea or not?

Thank you everybody for your comments,suggestions and technical reports from Australia,
I understand some of it as well!
My experience of "biggish"amps goes back to when I was 14, I built an 807 push pull amp which wasn't very good and while still at school built a PPP 6L6 guitar amp which served a while I was in a band.
A few years on and I acquired a "Kilowatt Star" valve audio amp from the works scrap dump, it cost me 50p (everything was 50p from there!) I didn't dare plug it in , the HT was near 3kV at 700mA .I sold it for £5 after a few months.
Anyway, to bring this to date project Williamsons .As somebody pointed out, I would have to get decent speakers , I did have a couple of Westrex 2080s 15" in huge reflex cabinets but sold them for a lot of money, too big for the house ,so along with the Leak 30+ , I have mediocre Goodmans RB20s and the set up sounds reasonable enough to my faltering ears.
Much as I would have liked to build these amps, and I do feel competent enough, they would take a lot of time to build, take a lot of room and do nothing for my carbon footprint what with multiple 807s and 5U4s warming the earth. Plus my deficient hearing and I think I'll leave this project to others and stick with the Stereo 30+.
I do have a TL12.1 ( new in 1951) and RC/PAU preamp to play with, so not vacuum deprived! Thanks again for your advice.
Bill
Bill is offline  
Old 15th Jun 2021, 3:50 am   #20
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 898
Default Re: Williamson stereo pair, a good idea or not?

If you'd like to donate the WWFB to Ed Dinning I'm sure he could fly it over to Oz as hand luggage when flights resume in a year or two
trobbins is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:11 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.