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Differences in tube idle dissipation and what it means at the end of a day
I have this Peavey Classic B amp from 1976, you know with the solid state preamp, and I am using it as a way to test/match 6L6 type tubes. So I had bought these unmarked "brand new" 6L6GC (supposedly matched) tubes a while back and the pair read 36ma and the other is at like 27ma. Of course the amp sounds pretty damn good with those unmarked Russian tubes albeit not a perfect match at all. All of those readings are with the adjustable fixed bias set to -55v on the grid. So I try another off brand labeled "6L6gc Made in China" and in about 30 seconds one of the tubes bias readings shoots upward with a nice sparkle, that's what I call a tube tester! I have a quad of "used old" Mesa Boogie branded 6L6GC's that I wanted to test out. Instantly those sets of tubes pull much more current with the bias voltage set to -55v and I up the voltage to around -65v or so. At this point I have a pair that sit at 36ma & 25ma and the other pair are 42-44ma to 40-42ma.
So my first question involves the fixed bias voltage... If I raise the bias voltage higher to -70v or even -75v then are then any concerns to "having" to raise the bias voltage so much? This also goes along with question 2... What does it mean if these "used old" tubes draw more current relative to the "brand new" tubes I had in the amp originally? To me it might mean - [pulls more current = stronger OR pulls more current = old weaker], maybe it does not mean either of those. So when tubes get worn out do they pull more current or less, or am I way off?
Lastly, I have a pair of old Sovtek 5881/6L6WGC tubes to test out as well. I have read up online about these tubes and from what I gather is that they are a "Power Horse" tube. However, in the tube data sheet they have ratings that include 250v max plate voltage. The Peavey is running a plate voltage at about 500v or as low as 494v with the Mesa Boogie tubes. The screen voltage is the same and there are no screen resistors on this amp. So, do I have anything to worry about testing these Sovtek tubes out on this amp? Also, why does the Sovtek tube data sheet state only 250v max plate voltage? My thought was that 250v was max plate voltage in class A single ended and to double it to 500v if in A/B push pull.
As always thanks for reading and thanks in advance for any feedback!
So my first question involves the fixed bias voltage... If I raise the bias voltage higher to -70v or even -75v then are then any concerns to "having" to raise the bias voltage so much? This also goes along with question 2... What does it mean if these "used old" tubes draw more current relative to the "brand new" tubes I had in the amp originally? To me it might mean - [pulls more current = stronger OR pulls more current = old weaker], maybe it does not mean either of those. So when tubes get worn out do they pull more current or less, or am I way off?
Lastly, I have a pair of old Sovtek 5881/6L6WGC tubes to test out as well. I have read up online about these tubes and from what I gather is that they are a "Power Horse" tube. However, in the tube data sheet they have ratings that include 250v max plate voltage. The Peavey is running a plate voltage at about 500v or as low as 494v with the Mesa Boogie tubes. The screen voltage is the same and there are no screen resistors on this amp. So, do I have anything to worry about testing these Sovtek tubes out on this amp? Also, why does the Sovtek tube data sheet state only 250v max plate voltage? My thought was that 250v was max plate voltage in class A single ended and to double it to 500v if in A/B push pull.
As always thanks for reading and thanks in advance for any feedback!
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