The ultimate power section? 6l6 el3 6v6 and cathode bias

[dragonbat13]

OK got a silverface twin. I never use four tubes. So in effect I have two pairs of sockets. I Want to design a setup that will allow the tubes in the title and allow for cathode bias with a switch for the correct bias for each tube. While I am not new at working on amps I am not the next Howard Dumble either.

My speakers are 16 ohm and I run an 8 ohm load into the amp. I plan on replacing the sockets with ceremic ones and mind as well mod the power section the way I want while I am at it. I am going to set it up to handle the EL34s today but am doing that just so I can get my solder smoke fix.

[mooreamps]

Have you considered instead of using a switch to toggle between the three tubes, install three master PA volume dial controls ? This, along with PA voicing, you could drive just one power tube, or have a blend of the three.

-g

[John_P_WI]

Dragonbat,

I did something very similar to a silverface bassman many years ago and it was well worth the time as it really "opened up" and made the amp very chimey.

I used a switch to change between two sandbox cathode resitors for "gross" bias changes and then individual pots for final individual tube bias adjusments. If you are going to change between tubes I would recommend individual adjustment pots.

You could also have EL34's in the middle tube sockets and 6v6's in the outer and lift the cathode of which pair you aren't using through a switch (except you are still drawing heater current on the unused tube....)

I ulimately just ended up using 6v6's because they sounded so good cranked.

John


I do remember that I used a Hammond 272JX transformer that gave around 400 v on the plates....

[dragonbat13]

My first step is to just rewire the sockets to use el34 tubes and try those and the 6v6 tubes

I am going to experiment and then decide how to do the permanent mod.

One thing I want to do is draw up a schematic once I am done.

I also dont really want to drill any more holes than I have to. I can use the ground switch for one switch.

I have also considered the individual bias pots