Guild Thunderbass 12DW7 question

Would have to see a schematic.

Could be lucky and just have bad tube.
In the dead channel.

Or any numerous number of guesses why stop working. Old sockets or connections gone bad just one of the few. Even simple as corroded input jack/ grounds.

Swap known good tube into dead channel you already have. See what happens. Check for dirty bent contacts while your there

12dw7 more likely be in the pre. Unless it has simple phase inverter. It's feasible if it drives output tubes. Higher current lower mu section of w7 be useful for driving output tubes. Otherwise be useful for driving tone controls

 

If you have the 8 tube thunderbass amp (rectifier tube, two 6550 power tubes, five small signal tubes), the schematic attached should be good to use. There are two 12DW7's. If not, you have a different revision that uses 6L6GC power tubes and has a four tube preamp, one of the tubes is a 12DW7. Both schematics are attached below.

The 12DW7 (7247) is a dual triode that is basically half 12AX7 and half 12AU7. Depending on the amps design, you might be able to substitute a 12AX7 for a 12DW7. But if the amp was designed for a 12DW7, that's what you should use. The question is, was the amp modified to use a 12AX7. You would have to look at the resistor values associated with that particular tube and compare them to the schematic to determine if the amp was modified.

But sure, you can install a 12DW7 as the phase inverter in the revision with the four preamp tubes. But if one channel is down, I'd trace that circuit from the input. The phase inverter wouldn't be the problem.

 

@Muckaluck - with respect neighbour, how much tube amp experience have you had? There are lethal voltages present in any tube amp even with the amp switched off. Take it back to your tech to repair the problem.

Regards from Scarborough!

 

A guitar player who thought he knew more that the designers of his amp but that was long ago.

 

Thank you but it was so long ago.

 

Yes, it helps to put the 12dw7 in the right spots Good deal.