Bogner Alchemist

[Mick Bailey]

Does anyone know the value of resistor R97 hanging off pin 2 of V1? this one illegible (could be 22R) and OC.

As usual, zero help from Line 6 for a schematic who just say 'take it to an authorised repair centre'.

[Mick Bailey]

It's actually 2M2. Had to remove the preamp board to trace the tracks and figure it out.

Interestingly, all the 2M2 resistors were OC, causing the amp to oscillate badly.

The ones to check if you get one of these are R97(V1) R38 (V4) and R39 (V4). Strange that they should all be faulty - possibly a bad batch?

[Jazz P Bass]

Strange indeed.

[J M Fahey]

Open Circuit or your multimeter over ranges above 2M ?
Looks the same on display, but itīs not the same.
And an open grid resistor would throw biasing off wildly rather than affecting stability or oscillations.
Of course, only guessing, donīt have the amp before me.

[cleeque]

causing the amp to oscillate badly

What does that sound like? Is it feedback, or a wavering sound?

I ask because I have a different amp that may have a similar problem.

[Jazz P Bass]

What does that sound like? Is it feedback, or a wavering sound?

I ask because I have a different amp that may have a similar problem.

That question cannot be answered generically.
Oscillation will sound like whatever cicrcuit is oscillating (the frequency)
A scope is a definite requirement.

[Mick Bailey]

Multimeter is fine - when I get something strange I check my test gear isn't playing up before coming to any conclusion. There are lots of components in this amp that seem to be there to tame oscillation -gain is on the extreme side.