Ken

Hey Ken,

I was told by Hot Tubes 70 to contact you regarding bias of a marshall 6100



I have a 1992 purple 6100SEV with EL34s. Just swapped all tubes. Plate voltage at 455V I thought of keeping the bias between 28 - 39mA, aiming for 34mA. I've done the biasing with 4 x probe meter and got the following readings:
V8: 34,3mA
V9: 27,5mA
V10: 53,4mA
V11: 36,4mA

V9 and V10 is way off! I bought 4 matching tubes from a guitar shop. I would thought that V8 and V9 or V10 and V11 would be off, byt not V9 and V10. V10 is getting really hot Fried eggs? The old tubes are not bad, so I tried putting an old tube in V10. approx same bad value...

My thoughts:
Should I change out R232 - R235, R237 and R238 with high precision resistors?

Got some small deviations in that area:
R232: ~5.63k
R233: ~5.62k
R237: ~5.62k
R238: ~5.60k

Is it an idea to install trim pots for these resistors?

Any other thoughts would be appreciated.

Thankz
Have a great Sunday,
Best Regards,
Jens

A Telefunken in V1 and a Black Plate Raytheon in V2 would do the job. You can get by with CP in V3 and V4. This would be $95 for the two tubes, plus $6 to ship.

Hey Ken. I sent you a friend's request. I should have done it a year ago. I thought I had, but I see now that I'm wrong.

It's hard to say value. People don't pay a premium for them unless they know what they are. The age and speakers make a difference. Get the age off a speaker code, and get the T# to get the model if you have the Marshall logo backs. I paid $375 for my A and I have the G12H80's in it (T2871), from Jan. 1980. 320 watts of capacity with the 120 watt sticker! LOL They usually sell for about the same price as a 1960 cabinet of the same vintage; mine was a little road worn but not too bad. I think I saved $100 over what it "should" sell for.

i have the 1982 a and b cab with small circle sticker reading "120watt" if you have any idea the value of this stack, it would be greatly appreciated. thank you