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PostPosted: 12 Dec 2018, 23:32 
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Joined: 22 Feb 2017, 07:55
Posts: 21
I originally bought the Edcor 7.6k transformers for a push pull 2A3 amp project. However, after continually moving (around and not using) a pair of Williamson mono block amps that I made over 20 years ago, I asked myself... are you going to listen to those amps or just move them aside when you are looking for something? I sat there and stared at them for awhile. The were not physically appealing, but they sounded good. After some thought, I decided to make two new chassis and give them a new look.

My version of the Williamson uses a surplus high voltage transformer which is very close to the original voltage that the original circuit used, but a few volts lower, so the power output is down slightly from the original version. It has also been converted to "Ultra-Linear". I used Hammond 1650P's to build the Williamson in 1996. I recall buying the 1650P model because it was cheaper than the lower wattage 6,600 PP Hammond at the time. Anyway, I also recall that some of the Williamson amps used a Stancor model output transformer that was a 7,600 load and I wondered if the Edcor could or would match the performance of the Stancor.

For the new chassis, I found two aluminum electrical service "panels/boxes" at my local electronic surplus store and converted them to a "retro chassis". They were a bit on the small side, but I knew if I was careful, I could squeeze each mono amp onto the new chassis. The Edcor transformer's performance is excellent. Based on the frequency response and distortion, I'd say the Edcor is just as good or maybe even better than the Stancor.

Power output is 22 watts RMS @ 1.5% THD+N into 8 ohms. I am also using the 6 ohm tap on the Edcor output transformer, which is also reducing the output slightly. I bought the Edcor with the 6 ohm tap because it would be a good compromise when using 4 and 8 ohm speakers. My main speakers are over 100dB efficient, so I don't need a lot of power.

I have been listening to singled-ended amps for the last few years and after hearing the Williamson's again, I forgot how good push pull tube amps with a little feedback can sound.


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PostPosted: 12 Dec 2018, 23:35 
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PostPosted: 12 Dec 2018, 23:48 
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Joined: 22 Feb 2017, 07:55
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Schematic...


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