Odd bias reading on Mod50...?

[memberzonly]

Just got a MOD 50 and decided to check the bias. Tubes are JJ 6L6GC. Reading test point 1, I got a reading of 28mV, so I bumped it up to 32, waited to allow any drift to subside and them moved on to test point 2.

When I checked test point 2, the reading was 52mV!! I have never see a tube this far out or this high before. Am I doing something wrong? Cosmetically, the tube looks fine....

 

[jmgman69]

Just got a MOD 50 and decided to check the bias. Tubes are JJ 6L6GC. Reading test point 1, I got a reading of 28mV, so I bumped it up to 32, waited to allow any drift to subside and them moved on to test point 2.

When I checked test point 2, the reading was 52mV!! I have never see a tube this far out or this high before. Am I doing something wrong? Cosmetically, the tube looks fine....

Could be a bad match,as it's hard to tell from just looking.

 

[jkdsteve]

power off, let her cool down, swap the tubes round and see if it follows the tube...if it does, you have a defective tube.

The danger in this approach is you're risking something other than a tube if it is bad....

The other approach is to go with known good tubes and re-bias....which of course risks a tube if it's the amp..

 

[memberzonly]

power off, let her cool down, swap the tubes round and see if it follows the tube...if it does, you have a defective tube.

The danger in this approach is you're risking something other than a tube if it is bad....

The other approach is to go with known good tubes and re-bias....which of course risks a tube if it's the amp..

Yep, it's the tube. Swapped sides and the readings followed the tubes. Off to buy a new set.....

 

[just42dave]

I buy my tubes from Ron sheldon at Cryoset online.
He does all kinds of shit before he sells his tubes ,,after about 100 tubes 50 power tubes I have never seen such work on matched tubes .NEVER!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!