This is a SET amp project from diytube.com using the 6B4G directly heated triode tubes. I was fortunate to get one of the last boards, now discontinued, and also grabbed one of the last available pairs of James OPTs. I modified the power supply from the original project to use a 6BY5 damper diode.

The design calls for a power transformer having 330v with two 6.3v filament taps, and a 6AX5 rectifier. I changed this to use an Antek toroidal transformer giving just 300v with more current to the filament taps. This allows using the 6BY5 rectifier, which has a nice ST shape. When I breadboarded this my B+ was a bit too high so I added a resistor before the filter choke and increased the RC resistors slightly. This gives me the target B+ and allows the circuit to run as it was designed. There are no other changes made to it.

Comments

• mwhouston
• 3 December 2017 at 07:38PM
• Never heard of the power tube. Nice to see a top plate in any other colour than black.

• vvelt
• 6 December 2017 at 09:46AM
• The 6B4G's are like a 2A3's, but the filaments are 6v and they have an octal base. The ones I have are NOS Sylvania, and Sovtek still makes them. This amp provides DC to the filaments. Also, I’m with you on using some color on top, makes things more interesting.