Peavey VK100 Heater Problem

[KCman]

My problem is I have 12v on the 6v connector HTR that leads to V1 and V2. I realize the 6l6 heaters are in series ending at V3 and then parallel to the others.
There is 32v on the connector feeding the 6l6 HTR1.
I'm reading 5v across each 6l6 heater (pin 2 to 7) and 12v at the end where it should be 6v.
Originally one of the 6l6 was completely dead, didn't even light on the tester. I figured that was the problem. All other tubes tested good.
I put all new 6l6 in and the tubes lit, but had the 12v instead of 6v. I then put the 6l6 on the tube tester with good results.
I replaced all 12ax7 and still have 12v on the 6V connector.

peavey_valveking_100_212.pdf

[TomCarlos]

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

[Jon Snell]

The heaters are DC and in series; 4x6L6 = 25v plus the 6v 12AX7 supply which inconveniently is not shown on your schematic.

[The Dude]

All that said, why not just measure voltage at the tube socket heater pins?

[g1]

The heaters are DC and in series; 4x6L6 = 25v plus the 6v 12AX7 supply which inconveniently is not shown on your schematic.

That is it. The point marked '6V1' does not come from a supply, it goes to V1 and V2 heaters which are in parallel with V3. They are shown in the lower right corner of the power amp schematic.

KCman are both sides of all preamp heaters lit? All power tubes heaters lit?

[Jon Snell]

Thanks G1, didn't notice that!
Well spotted.
Veru confusing for some.

[KCman]

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?

[g1]

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?

[Jon Snell]

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.

[KCman]

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?

[x-pro]

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.

What a "miraculous" inclusion of lamp heaters.

[x-pro]

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.

You can. Only an additional transformer will be required for the corresponding voltages and the required power.

[Jon Snell]

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?

1/ You will find, one has open circuit heaters or has/had a bad connection on pins 2 or 7. ALL heaters must be in circuit to pass the heater current to the next section. Parallel heater; if one fails too much current will flow through the remaining causing damage.
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.

[KCman]

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.

[g1]

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.