I am a great admirer of Karel Mars' amps and follow his posts with interest.
A while back, noticing that RS Components offers nice new output transformers suitable for a push-pull EL84 amp, I decided to try them. The SA link for the OPTs is https://za.rs-online.com/web/p/audio-transformers/1237240/ and they are priced at about each. Model number: D29A09F. They are 10W, PP designs with 6k6 primary impedance, with ultralinear taps. 20% if I recall correctly.
I first tried them with a design similar to Karel's Mars EL84PP circuit, which I had used before, but my layout was not right and there was too much hum. The fact that I was using parts from a scrap oscilloscope as a chassis didn't help. I tried to fix the hum, but without success. Then I decided to build Karel's circuit and follow his layout as much as I could, The slots already in the chassis meant that I had to put the valves in the front, and I decided to put the power transformer inside the chassis. But as far as possible, I followed Karel's schematic and photos. The result is very pleasing and is playing some smooth Ben Webster jazz as I write.
I'll put a couple of pics in the following post.
Once again, my appreciation for all that Karel does to help us build and enjoy valve amps.
A while back, noticing that RS Components offers nice new output transformers suitable for a push-pull EL84 amp, I decided to try them. The SA link for the OPTs is https://za.rs-online.com/web/p/audio-transformers/1237240/ and they are priced at about each. Model number: D29A09F. They are 10W, PP designs with 6k6 primary impedance, with ultralinear taps. 20% if I recall correctly.
I first tried them with a design similar to Karel's Mars EL84PP circuit, which I had used before, but my layout was not right and there was too much hum. The fact that I was using parts from a scrap oscilloscope as a chassis didn't help. I tried to fix the hum, but without success. Then I decided to build Karel's circuit and follow his layout as much as I could, The slots already in the chassis meant that I had to put the valves in the front, and I decided to put the power transformer inside the chassis. But as far as possible, I followed Karel's schematic and photos. The result is very pleasing and is playing some smooth Ben Webster jazz as I write.
I'll put a couple of pics in the following post.
Once again, my appreciation for all that Karel does to help us build and enjoy valve amps.
