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Hello, I recently built another amp that I thought might be of some interest/help to others here on the forum. I had an old, broken donor hi-fi with a 6V6 push pull amp in it. Having already built a 5E3, I tried a few wrinkles mainly just to learn more about tube amp circuits. I decided to re-use the chassis and make this amp a platform for experimenting. I gutted all the wiring except the filament wires. I enlarged the pre amp socket holes and added octal sockets for a 6SL7 input tube and a 6SN7 paraphase inverter. I changed the 5D3 circuit to single channel with split cathodes on the input and have a blend control on the input triodes (thanks Bruce and Hasserl). There was faulty humdinger which I replaced with a fuse for the secondary filament wiring (thanks RG). I haven't added the fuses for the other secondaries yet. I also used the elevated heater technique by connecting the heaters to the cathode at the power tube socket. It works well, the amp is quiet.
The amp has a warm singing tone, and has more clean headroom than my 5E3 build. Some warned me I might have problems with the paraphase inverter, but it seems to work quite well. The first 6SL7 (used) I tried was microphonic. I have a 6SL7 WGT in there now with no problems. I decided to try point to point with terminal strips to practice lead dress and because an eyelet board would have a real challenge to fit in the old chassis. Another thing I tried was to use carbon comp resistors only where they might add their mojo (per RG's article). Note that I put the indicator lamp last in line in the filament wiring. This has proved to be a bad idea. I have burned out 2 lamps in short order.
One question I have is, the OT has 3 secondary wires (multiple ohms). Two were unused in the original amp. I am now using the original wire and have the other two shrink wrapped. With the same 8 ohm speaker as my 5E3, this amp is a little less loud. Not drastically, but I am curious if there is a simple test I could perform to identify those taps. Any suggestions on this (and the amp in general) are greatly appreciated as always.
The amp has a warm singing tone, and has more clean headroom than my 5E3 build. Some warned me I might have problems with the paraphase inverter, but it seems to work quite well. The first 6SL7 (used) I tried was microphonic. I have a 6SL7 WGT in there now with no problems. I decided to try point to point with terminal strips to practice lead dress and because an eyelet board would have a real challenge to fit in the old chassis. Another thing I tried was to use carbon comp resistors only where they might add their mojo (per RG's article). Note that I put the indicator lamp last in line in the filament wiring. This has proved to be a bad idea. I have burned out 2 lamps in short order.
One question I have is, the OT has 3 secondary wires (multiple ohms). Two were unused in the original amp. I am now using the original wire and have the other two shrink wrapped. With the same 8 ohm speaker as my 5E3, this amp is a little less loud. Not drastically, but I am curious if there is a simple test I could perform to identify those taps. Any suggestions on this (and the amp in general) are greatly appreciated as always.
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