Valveking 212 Repair

[7xa12]

Peavey valveking 212 repair
I need help
what is correct voltage MM readings for Valveking 212 for all preamp/ power tubes pins to ground? (with no tubes installed) I have 470V on V1 pin 1 preamp tube, Is it any stress/ excessive voltage exposure for other components with no tubes installed? Are the valveking filter caps are properly rated for the margin, (550V?)

[Enzo]

Voltages in an amp with no tubes installed are pretty much meaningless. Voltage readings are always taken with all the tubes in place. The amp voltages are fine, as are the caps they use. With tubes installed, none of the tubes will see voltage that high.

[7xa12]

Thanks Enzo
I had a T3A F203 fuse blown and two rectifiers diodes D207 and D208, I replaced all 4 diodes with IN4007 and I have pilot light back and 38Volts on R213 resistor both side. ( on the heater supply I guess?) Is there no point to measure voltage on R213 without tubes? I have a pilot light back and no fuses blow, but that does not mean that I have heater (?).
I have a new set of JJ 6l6Gc tubes- schould I power on the amp with all new tubes installed?
Thanks for your help again

[7xa12]

Enzo, What are good voltage readings for power and preamp tubes pins with all tubes installed? should I install the new set of tubes without a risk of frying them?

Voltages in an amp with no tubes installed are pretty much meaningless. Voltage readings are always taken with all the tubes in place. The amp voltages are fine, as are the caps they use. With tubes installed, none of the tubes will see voltage that high.

[Enzo]

OK, let me relax my rules a bit. Telling me you have 470v on a preamp pin with no tubes doesn't help me. But if you have to repair a power supply, then certainly it can be useful to test just to see that the supply functions. I mean if you got zero volts instead of 470, we'd know your supply was missing or dead.

The problem is that without the tubes, none of the supplies are loaded at all, and the voltages ALL go way high.

If you now have +38v on R213, then the supply you fixed seems to be working. In fact, I;d wager that without tubes you probably still have 38v on both ends of the 400 ohm R212 also, instead of 14v. Not only that but while it won;t automatically blow them up, those 35v caps don't need to see 38v. By installing the tubes, the supplies are loaded, the transformer voltages come down some, and the supplies settle into place.


38v sounds like it isnt out of hand. I wouldn't have predicted 38, but if I REALLY wanted to know, I;d measure the AC from the transformer at P211-P215. Then calculate the expected DC. Going in reverse, I bet you have roughly 26vAC there. The voltages are not likely to be "wrong." In other words, you 38v supply probably won;lt wake up one day and be 49 volts. It might come up missing, or a bad filter cap might leave it really low and full of ripple/hum. SO as a tech I work on expectations, not a chart. If I look at pin 1 of one of the preamp tubes - that is a plate pin on a 12AX7. I don;t know what I might find, even schematics that have voltages are just ball park amounts. But I know if I find really high voltage there - like the same as my power supply, then teh tube is not conducting, and if I get zero there, same thing but for different reason. What I want to see is something in the middle. If I have a 300-400v B+ for the stage, then I expect to see something in the 150-25v range on that plate. I expect most 12AX7 circuits to be conducting roughly a milliamp or two, so the typical cathode resistor will drop a volt or two.


But generalities aside, your Valve King has its tube heaters all wired in series. Without ALL the tubes installed, NONE of the heaters will come on. Look on the schematic page with the power tubes, upper left corner plus a couple more lower right corner. Right now you have 38v on R213, which then means 38v on the point marked HTR on the power supply, and then HTR1 on the power tube page. And if you measure pin 7 of V4, without tubes, you'd find your 38v there too. But you would not find anything but zero on all the rest of the tube heater pins.

With tubes in, then the heater current flows through all the tubes, and Ohm's Law drops voltage across each one. There are five tube heaters in series across your "38v" supply and ground. The last one on the left is a 12AX7, and has two more of them in parallel from the lower right. So with tubes, you will get roughly 6v across each tube, so 38v at V4-7, 32v at V4-2, 26v at V6-2, etc. Now since these are 6.3v heaters, and there are five in series, That adds up to 31-32v, and with the amp full of tubes, I suspect your 38v will be pulled back down to closer to that 32v figure.

[7xa12]

thank you Enzo - I have learned something new and that is great that people want to share their knowledge and experience with others.
I like the amp, is that anything that I can do to improve components protection/avoid the disaster when the power tube fails? ( would be any better type of fuse for F203?) I am still thinking about the diodes 1N4003 -I replaced with 4007, that must be the good reason why they used them ( 200V?) So I will install all the tubes, turn the amp on, I hope no faults with channel switching, or reverb section in my case, anyway I hear relay click when turning the amp off (after a few seconds)...

[Enzo]

They only used the 200v diodes because it is a 30v circuit, not the 500v circuit. In the B+ circuit they DID use 1N4007.

The problem with trying to make an amp so that NOTHING can cause any damage when it fails is that it won't work, or the amp will be so bogged down with stuff it can't operate. When power tubes short internally, they often burn up a screen resistor. I can mount really heavy duty screen resistors, and they will no longer burn out, but the failure current is still going to be there, so somethinhg else will burn up. SOme power supply part or maybe a copper trace burns off a board. Sometimes you protect one thing which causes a worse problem elsewhere.


Tubes fail, they sometimes cause other damage. We usually have no troubloe fixing whatever happens. I consider it just a fact of life. ENjoy the amp and don;t spend too much energy worrying about the armageddon of the power tubes.

[7xa12]

I will put the sentence on my T -shirt "Sometimes you protect one thing which causes a worse problem elsewhere." that is the fact of live, and who say that Electronics is so far from real live ? hahaha

[Prairie Dawg]

Here's my adventures with a valveking. Sounds about like your deal. Power tube shorts out and by the time the fuse says "wait a minute-something's bad here!" the damage to all the low voltage stuff on that circuit is done.

Judybox Revival: Resuscitating a Peavey Valveking 212

[7xa12]

I have installed all the tubes, turn it on and it works, on standby and with both switches on, fuses hold. It draws about0.50 - 0.60 A from the mains outlet and power 57Wat on standby and 140 W when both switches on play (cheap Power Meter model DEM 1379 pluged into main socket) . When flip from standby to play some irregular cracking sounds and static from the speakers occur, but after a while they seemed to be lower but still present. (I used a contact cleaner on tubes pins before instalation)
( I had very little cracking noises before the amp failed, but they didnt used to be constant and present all the time)
all the pots are at minimum. Now I will check the amp with guitar, and then planning measure the voltage on R212 and on the preamp and power tubes pins to ground.
Thank you Praire Dawg - your adventure with the amp has helped/and I hope will help me too. The learning value I am getting from Enzo and from you is the positive side of my amp fail. (sorry for my English I am not a native English speaker)

[Prairie Dawg]

I am glad that my scribblings could shed a little light on this for you but Enzo is the brains in this outfit.

[7xa12]

With all Tubes installed, I have 32V (heater side) and 22V (+14v side) on the R213 resistor. On the V4-Power Tube - pin 2 heater 25V pin 3 plate- 458V, Pin 4 screen grid 453V, pin 5 control grid (-047V) and pin 7 heater 32V (Enzo was right ) tubes seemed to glow orange and partly (little) blue. Am I frying them? when I plug in the guitar would be more stress for them? Any advice/suggestions? thanks

[7xa12]

am I frying them too fast? that was I wanted to ask.

[7xa12]

I fixed my Valveking. I was lucky, just 2 diodes and fuse. I soldered a fuse holder too. I was very cautious and slow ( safety gloves, chop stick, even rubber gloves (I had left hand in the pocket..too) . I have big respect for the high voltage present in the amp. I like the amp more with new set of JJ 6l6GC and Tungsol in V1. Enzo and Praire Doug Thanks for your help. now its time to play.

[Jazz P Bass]

I am glad that you got everything sorted out.
Note:
The glove thing is great but it can be very cumbersome ( and even dangerous if you fumble something).
Your best bet, now that you have respect for the high voltages in an amp, is to learn how to work with the dangerous stuff.
Amp off, put a meter on the B+ & then drain the caps.(1K, 2 watt resistor to ground)
And unplug the amp from the mains supply when you are in there.
That is safe.