1961 Fender Bassman 6G6 Bass Channel

[Helmholtz]

Yeah I replaced the yellow .25 astrons with .22 Jupiters.. I could have sworn it was bad astrons, but it didn’t make a difference. I mean, once this issue is resolved I’m eager to see if the Jupiter’s are considerably better. Kinda sounds bad right now though

I meant all yellow Astrons, including 0.1µ and 0.05µ types. I measured many yellow Astrons and all of them showed more or less increased leakage. You may test for leakage by disconnecting the low voltage side (in case of doubt just measure both sides) of the cap and connecting a DCV meter between the open lead and ground.

[Steelwitch]

I meant all yellow Astrons, including 0.1µ and 0.05µ types. I measured many yellow Astrons and all of them showed more or less increased leakage. You may test for leakage by disconnecting the low voltage side (in case of doubt just measure both sides) of the cap and connecting a DCV meter between the open lead and ground.

The two .25’s were the only astrons in the bass preamp! The rest are blue molded and tested fine, basically every cap after the second gain stage has 4vDC on it

[g1]

The thing with the conductive eyelet board is they can pick up moisture. That is what the wax is supposed to prevent. If the heat will dry it out, sometimes that is all it takes.
Other times, there seems to be more problems than just moisture, the pigment can be conductive.
So it's sometimes simple, other times not. I don't live in a real humid area, so haven't really had to deal with it much. Others in humid places sometimes have to replace eyelet boards.
I think the board can take quite a bit of heat before in burns, but the components not so much. You may have to lift them if you want to put a lot of heat on.

[Helmholtz]

There is however about 6vDC leaking onto the treble pot

It is normal to have DCV on the treble pot with this circuit. It is actually floating on the DC potential of the PI input grid (around 30VDC). Depending on the input resistance of your meter the reading will be lower.

[Steelwitch]

That makes sense, it looks like there isn’t anything decoupling the tone stack and the PI input, I didn’t consider that!

[Steelwitch]

Just wanted to update y’all about this repair— after talking to the customer we agreed replacing the eyelet board with a more modern and robust turret board is best if the components need to be removed anyway. It’s ultimately not that much extra work and watts tube audio seems to offer a really nice replacement! He asked me to make some of the changes need it to match it to a 6G6B instead, and replace the ground switch with a switch to go between tube and solid state rectification. Rob Robinette has a simple and easily reversible mod on his site that I’m going to work off of! It sucks that this amp basically needs to be rebuilt but I’m excited to get to do some primo stuff to it will post pics

[Steelwitch]

I just wanted to update everyone on this repair! After speaking with the customer we decided that the best route would be to replace the old eyelet board with a more modern g10 turret board, update the circuit to a 6G6B since he mainly uses this amp with both channels jumpered. were doing a rebuild anyway, he wants me to replace the ground switch with switching capability between the tube rectifier and solid state. I’m pretty excited about the mods specifically. Will update with pics!

[Tony Bones]

With all the bad press that Watts Audio has been getting, I would avoid them.

Doug Hoffman sells very good turret boards. hoffmanamps.com