Peavey PK100

[patlaw]

I'm looking for some tube amps to repair for fun. Here's a Peavey PK100 that's available for $75 but without tubes. Would it need four matched 6L6s, or would two matched pairs work? Your thoughts on this amp?

peavey_valveking_100_212.pdf

Matched Pair 6L6

[Leo_Gnardo]

"Fun" and "Made in CHINA" don't go well together. Unless you insist on being a masochist. Or ripping out the whole interior and building a new amp in the chassis. With few exceptions MIC are disposable. $75 seems about right, you get a box, a chassis and a pair of transformers.

Set of matched output tubes, yes that's an excellent idea. Anything less, why would you want that. They will eventually diverge with use. Best to start off on the right foot, no matter what amp.

[Enzo]

A bazillion tube amps are made and sold every year. All those Fenders and peaveys and MArshalls do not come with matched power tubes. yet the amps work just fine. At the factory, they reach for four 6L6s from a big box and stick them into the amps. We may prefer matched sets, but the amps don't care.

The peavey branded tubes you linked come in pairs, but that same store sells matched quads of several brands. Why buy two pairs when the same store sells sets of four already?

[Leo_Gnardo]

We may prefer matched sets, but the amps don't care.

Really? You mean I can stick in a quad where one's drawing 10 mA, the next 30 mA, the next next 50 mA, and the last one 80 mA and the amp will run just fine, deliver maximum clean power, long life, no plates going red, and not buzz from DC imbalance in the OT primary windings?????

Gosh I never knew that. Drat all the time I've been wasting. You're right, those rock guitarists just want distortion, and they're so deaf and they play so loud they'd never hear that buzz anyway.

Ya learn something every day. :P What a susprize.

I'll be putting in my application at McClowns Monday morning. Want fries with that? I hope I got that part right. Heck, just let me push the broom if you could trust me to do that. Wouldn't want to strain what little talent I have.

[Enzo]

I'll ignore the sarcasm. Disagreeing with you is not a personal attack, it is just a difference of opinion. And if I have misread your post intent, I apologize in advance.

I recall a famous photo of Eddie Van Halen taken from behind his amp on stage, and we clearly see he has only three power tubes in his amp head.

Your proposed set of four, well, if a tube is drawing 80ma, then it is likely defective, or at least the bias needs adjusting.

Look, I buy matched sets myself, main benefit is hum balance. Anyone can spend the extra dollar a tube for that benefit, worth four dollars to me, but not to everyone, since more noise comes from the preamp than those unbalanced tubes in the output. You generally adjust bias for any set of tubes, so if one wants to draw 80ma, we turn the bias so it draws more reasonably and doesn't red plate, and then those cooler tubes will also not red plate. One hopes that buying bulk tubes from a supplier, they do not usually come that spread out anyway.

If I were to guess, I'd expect random tubes from the case to range more like 20-40ma. But in any case, I don't see mismatching as shortening tube life, and red plating comes from misbias. Remember, I DID suggest the OP consider a set of four instead of two pairs.

The underlying point I try to make is that bias is not some supercritical thing, it is just an idle adjustment. We may desire to have matched sets, some guys arrange a bias adjuster for each side of the push pull, and some even have four bias tweaks, one per tube. If they like that, fine, but it is overkill. They have been making Fender Twin Reverbs for decades, long before matched sets became common. They were and are killer amps, even with the random tubes they come with. Now with a 100 watt amp like that, perhaps by carefully selecting tubes and so on, I could get an extra 10 watts of maximum clean power. OK, but how many among us will hear those 10 extra watts?

For any tube, you can bias it too hot, and it will red plate, and you can bias it too cold and get excess crossover distortion. But in between those extremes is a wide range of perfectly acceptable biasing. Factory settings on Peavey 5150 heads commonly sit in the 15-20ma per tube range. Fender HR DeVille is to be biased at 30ma a tube. This 70% stuff is a mantra of hobbyists.

An amp with a random set of tubes will work fine. Can you tweak it so you like it better? Probably so. Would you prefer that certain whatever that matched tubes provide? Probably so. But without having a matched set, the amp will still function and sound as good as most amps.

Imagine as so many guys do, instead of buying a quad, they get two pairs. Generally one pair will draw higher currents than the other, so what is usually done is the pairs are split. Pair A is split to the push and the pull sides. Then pair B is done the same. SO the push has an AB, and the pull has an AB. If we assume something like 30ma for one pair and 40ma for the other (per tube), we wind up with a 30 and a 40 for a total 70ma per side. AMp sounds fine. Now rearrange the pairs so both A are on one side and both B on the other. Now we have 60ma on one side and 80ma on the other. That's a largish mismatch, yet I'll wager 95% of amp users would not hear the difference.

We see people every day asking things like is it OK to use a 250v fuse in place of the 125v fuse in their amp. Or is it OK to use a 500v cap in place of a 450v one. I don't want some young experimenter thinking he can't build or repair an amp just because he doesn't have a matched set of tubes.

[J M Fahey]

I'm looking for some tube amps to repair for fun. Here's a Peavey PK100 that's available for $75 but without tubes.

Depends on your definition of "fun"
To be more precise, in principle it *is* repairable, the design is quite sound, .... and it is a Peavey, made in China but by them, not a relabelled generic amp like so many others; the point is we don't really know what happened, it might simply have shown a defect one day and the owner didn't want to pay a Tech or on the other end it might have a dead or shorted transformer (which would be a deal killer) or the PCB might be a mess, either it caught fire and a section is unrepairable or some tyro got at it with a 1000W soldering iron and achieved about the same.
If betting $75 is fine for you, go ahead.

I'd buy the amp as is but no tubes yet.
First open it, check visually that inside it's not Hiroshima the day after The Bomb, that carefully turning it on (into a bulb limiter for safety) brings up expected filament, bias, screen and +V voltages (somewhat higher because of reduced load) and only then sink another $70 or so in power tubes.

Would it need four matched 6L6s, or would two matched pairs work? Your thoughts on this amp?

Both options would work.
Coming straight from Peavey they should be reasonably close anyway.

That said, when he says "no tubes" he means it, you'll also need the preamp tubes so add 4x12AX7 (or is it 5?) to the bill.

[g1]

He's basically said it doesn't work but the tubes did.
If you've got a bunch of used tubes then it's no big deal, maybe still a little overpriced.
If you have to buy tubes, now you're at $200 with an amp that still doesn't work.
I think there are probably better candidates for less money, but depends what you like.

[R.B. Diver]

HELP!!! I do not know how to post this but can anyone please tell me why my bias cap and 10k res are suddenly getting to hot?

[g1]

HELP!!! I do not know how to post this

Up at the top of the page, click on "maintenance, troubleshooting and repair". When the new page comes up, click on "+Post New Thread".
Be sure to mention the Brand and model number, fault, and if possible the schematic.