Squeal when OD Drive is past 5 and more

[caricbrown]

I am converting a bassman based on the specs found here. So far so good, but the OD sound is not very smooth and I have two other issues: 1) A squeal is heard when OD Drive is past 5. Master and OD Level can be at any setting.
2) The sound fizzles and completly dissapates if the Clean level is past 3 while in OD.

I checked the voltages on V2 P1 and they seem to get too high while playing and the clean level is increased.

All is perfect while in clean, sounds better then stock!

Any suggestions on what to check? Thanks.

[Bob-I]

It sounds like you have a high frequency oscillation in the OD stages. Can you post some pictures?

Do you have shielded wire going to the grids of V2?