I've been really sick and didn’t do anything for over a week. But, when getting the other tubes back out of their package, I noticed someone put el34s in the 6l6 boxes. That’s why each tube had the same low voltage. They all had the same 1.5 amp heater draw!
Not sure how they got switched. They were supposed to be new. Glad I caught it, just surprised I didn’t notice the physical size difference when putting them in.
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Peavey VK100 Heater Problem
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Try one in with 3 of the new ones and see what you get. Then try the others one at a time. My guess is the old are all equal, but off spec.
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So, I got to thinking. All 6l6 had 5v across from pin 2 to 7. If only one was drawing more current or had a dirty socket, wouldn't only one have lower voltage? Why all 4 had only 5v? When I changed out all the 6l6 (which fixed it), I didn't touch the 12ax7 tubes.
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Originally posted by KCman View PostThe 6l6 were Sovtek and the 12ax7 are all JJ. But, I threw another new set of 4 6l6 in and now the voltages are correct.
So, that means 1 or more 6l6 were pulling more current on the heaters than they should be?
Second question;
If put in an amp that has "normal" heater wiring (all parallel), would those tubes be fine? They test all right on the tester, not super strong, but good.
and how would I know which tube or tubes it was, without trying one at a time with the known good tubes?
2/ If they test OK, there was probably a bad connection in the heater connections.
All 12AX7s MUST be working to allow the current to flow. If one fails, the other two will also fail.
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Originally posted by KCman View PostSecond question;
If put in an amp that has "normal" heater wiring (all parallel), would those tubes be fine? They test all right on the tester, not super strong, but good.
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Originally posted by Jon Snell View PostIf a 12AX7 is removed and powered up, the other two will burn up, leaving no heater current for the 6L6s.
Likewise if a 6L6 is removed, ALL valves will go cold.
If a 12AX7 valve base has a dirty contact on either pins 4, 5 or 9 of any valve, the remaining 12AX7s will fail.
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The 6l6 were Sovtek and the 12ax7 are all JJ. But, I threw another new set of 4 6l6 in and now the voltages are correct.
So, that means 1 or more 6l6 were pulling more current on the heaters than they should be?
Second question;
If put in an amp that has "normal" heater wiring (all parallel), would those tubes be fine? They test all right on the tester, not super strong, but good.
and how would I know which tube or tubes it was, without trying one at a time with the known good tubes?
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ECC83/12AX7 draws 300mA for both sides; 4&5 to 9.
Three valves in parallel = 900mA.
A 6L6 draws 900mA.
If a 12AX7 is removed and powered up, the other two will burn up, leaving no heater current for the 6L6s.
Likewise if a 6L6 is removed, ALL valves will go cold.
If a 12AX7 valve base has a dirty contact on either pins 4, 5 or 9 of any valve, the remaining 12AX7s will fail.
Measure the voltage across any 6L6 or 12AX7, the one with 30volts across it is dead.
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There must be an imbalance in the heater currents with something not matching the traditional specs. (assuming the 12AX7 heater wiring has not been modified from schematic). Double check that the 12AX7's are measuring the 12V from pin 4 to 9, not 4 to 5.
The 3 AX's, with heaters all running parallel should run 900mA. A 6L6 heater should also run at 900mA.
So you should have the equivalent of five 6L6's in series, each dropping the same voltage across. If the voltages are not lining up, and it is wired up as shown in schematic, then there must be some discrepancy of the heater current either in the 6L6's or the 12AX7's.
What brand and specific types of tubes do you have there?
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TomCarlos Thanks for the link. I had already confirmed the flow of the heater circuit that is listed there. I assumed something was out of balance, causing the 12v.
@g1 All of the heater are lit. Both sides of the 12ax7s and all 4 6l6.
I have 32v supplying the chain HTR1. The 6l6 only measure 5v across pin 2 and 7. That leaves 12v where it should be 6v. What could cause the 5v at the 6l6?
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Originally posted by Jon Snell View Post
KCman are both sides of all preamp heaters lit? All power tubes heaters lit?
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All that said, why not just measure voltage at the tube socket heater pins?
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Just for reference, there is a post titled " Peavey Valve King - No Heaters." Take a look at that post and use it as a checklist to debug your problem - https://music-electronics-forum.com/...ing-no-heaters
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