Peavey Ultra Plus "gotchas"

[gui_tarzan]

Yes I searched and read before posting this, are there any odd gotchas to watch out for? I put a new set of matched 6L6s in it, cleaned the pots and sockets and jacks and did a cursory twice-over looking for bad solder joints. The customer said it was "popping" which for now I'm blaming on a broken getter floating around in one of the old, very mismatched power tubes. All of the caps look good but it's harder to tell with radials than the older axials. I've seen bulging caps in some older PCs but haven't yet in a newer(ish) guitar amp.

[Enzo]

It is just an amp, like so many other 100 watt tube amps, and very much like all the other large PV amps. I don't know what sort of gotchas you might be expecting.

[gui_tarzan]

For example "resistor X usually fails open" or "cap X is known to leak DC badly". That type of thing. I know it's just an amp, but everything has its own set of quirks. I'm just trying to learn as much as I can about as much as I can to do the best job I can.

I don't have the benefit of working in an amp shop for two or three or more decades like some of you guys, but I'm sincere about learning so I can help keep these things running after you guys have retired/assumed room temperature/moved to Jamaica and are sipping fruity drinks with umbrellas on the beach.

Ask me about 1964/5 Buick Skylarks and I can pretty much tell you anything you want to know. I've owned and/or rebuilt many of them since I was a teenager. See what I mean?

[g1]

I think he wants to make sure you don't short-cut the troubleshooting process. You will learn much more going through the process and it will be applicable to other make/model/faults. And, as you said, you want to learn as much as possible.
Let me put it this way: suppose you didn't know anything about skylarks, and did not do your own work, but needed something fixed. Would you rather get the guy who knew all the faults because he had found them out, and knew why they happened, or the guy that knew the common faults because he found them on the web .

[gui_tarzan]

I get that, G, I really do. I just appreciate it when someone says "hey, watch out for this on that model", you know? I'm not looking for the easy way out, I was just asking if there were common issues that stand out.

[Enzo]

I hear you, but the problem with that is everyone seems to think there are such lists, and there are not. There are a few things that come up a lot, like the power tube socket pins in a Fender HR Deville, and similarly made other models. But that last phrase is the kicker. The Utra and Ultra Plus, not to mention the 5150, the XXX, the JSX, the 5150-2, and whatever ones i am not bringing to mind, are all designed by the same guys, built on the same production lines, of the same materials. generic problems are largely gone from years and years of production and engineering. WHEN THERE IS A PROBLEM, we may know that certain things are more likely than others to cause THAT PROBLEM, but that is not at all the same as saying THAT PROBLEM usually occurs.


Here is one for you. PV has a light for the standby switch, usually called "status". Usually green. IF that light is out, IF, the amp will be silent, and that will be because the high voltage is missing. Why is the high voltage missing? Most common reason is a blown high voltage fuse. And what is the most common reason for a blown high voltage fuse? A failed or failing power tube. Now IF we have no high voltage, and IF we have a blown HV fuse, and IF we had to replace a power tube and there STILL is no high voltage light. THEN, I'd suggest you look for an open 400 ohm resistor in the power supply. That is the resistor that serves the screens node on the power supply, and failed power tubes often take out a screen resistor. So there it is. If I just said "watch out for an open screen node 400 ohm resistor", That would be misleading. You would then open the amp and look for a resistor to check when it really only comes up after those several IFs.

There is no part that "usually fails". ANything like that and it would be redesigned at the factory. The consuming public is so mightily paranoid as it is. Case in point, the PV JSX. The very first batch off the production line has a resistor value - hey another screen resistor - at the power tube that failed more than it should ONLY IF you used the E34L version instead of the EL34. One brand and model of the EL34 that tended to have higher screen currents. The amp didn't always fail. But IF you used that particular tube, there was a higher than normal occurrence of this problem. Not everyone using that tube had the problem, just more than normal. They quickly made engineering change orders to prevent this, and the JSX continued on without that concern. Use any EL34 version you wanted. That was 10 years ago. To this day, the company still gets calls and emails as well as forum postings asking "how do I tell if my JSX has 'the problem'?" An issue that affected only the very first run, and only for a small portion of the amp owners, yet in the public eye, this would be on the list of "common problems".


Here is a common one for you, the PV Classic 30...

No wait, when I tell these stories, there will be people who read it and think, "Geez, these Peavey amps must fail all the time." And that is not the case. I don't use them as examples because they break down a lot, I use them because they are something most people are familiar with, and like the most popular brands of anything, the more they sell, the more of them will come in for service. That is another problem with common problem lists, people interpret them to mean these things break a lot. I had three Fender Hot Rods in my shop once and one Vox Cambridge 30. Someone came in a saw that and said, "Looks like those Fenders are not as reliable as the Vox amps." No, exactly wrong. The store that sent the amps to me got in three of the Vox amps, and all three had problems. The Fender amps were selling by the truckload, so it was several of a zillion Fenders or ALL of the Voxs. But people rarely put it in context. It is that same WHEN there is a problem versus this breaks a lot.

PV Classic 30. There are three circuit boards. They are connected together by rows of short bare wire jumpers. Due to vibration, those jumpers break more often than the usual wiring in an amp. So IF someone has certain types of problems, we suggest checking for a broken jumper wire. Lots of other problems that wouldn;t involve those wires. It doesn;t happen to every amp or even most of them, it happens to some. It would be counterproductive to tell someone to go check that when it wasn;t likely involved.


So you tell us something that is wrong, and we can probably tell you things to look at before other things, but that is not the same as calling the things common failures. I know saving time is a good goal, and learning, well, I appreciate your efforts to learn. But instead of look-up lists, the best thing to learn is how to troubleshoot. I have a little clumsy philosophy on a sign around here:

Troubleshooting will get you through times with no schematics better than schematics will get you through a lack of troubleshooting.

And that brings me back to that PV. I am intimately familiar with the amp, but were I not, and that 400 ohm resistor thing was the case, I would find an amp that was silent. I'd see the power light on, and the tubes lighting up, and I;d see the status light dark. I'd look in the schematic to see the status light turns on when the screens B+ is present. Opening the amp, I'd check the HV fuse, I;d check for B+ at the tubes, and absent screen voltage but HV present otherwise, I'd pretty quickly see the screen resistor in the B+ supply, and it would be 400 ohms. I'd see if it were open. What else could cause that? Oh, a bad standby switch, a burnt trace, other things. But those steps are what I would be checking on any other tube amp too.


I know a few things about Skylarks, they come in metallic mint green, just like a Pontiac GTO, and they are NEVER confused with a Corvette.


I bet if someone brought you a Skylark pulling hard to one side, and you knew a common problem was a bad toe-in valve, (yes I made that up) I bet you'd still first look it over for a flat tire, a collapsed shock (or strut or whatever they have), or if the car sits funny before you went for the valve kit.

[tedmich]

^^ what he said!

also "common" Bad SGRs, replace with ~1k 5w

[gui_tarzan]

What you said, as always, makes a lot of sense. I know your time is valuable and I appreciate you taking the time to go into it in detail. I did another look-see with the magnifying glass at the components and what solder joints I can see without taking it all apart just to make sure I didn't miss anything obvious. And yes, troubleshooting ability always trumps common "knowledge". I'm working on it. The more familiar I become with different amps and schematics the easier it is to fix the next one. I'm constantly looking at them in order to familiarize myself with the circuitry and trying to learn the theory while I'm at it.

The car analogy is a good one, and having been a shadetree (and at one point a working) mechanic most of my life I know there are certain parts on certain cars that wear out or just fail after a period of time. Specifically on my old Buicks they all have part "X" that is a bugger to fix but one of the first things you look for when you get one. It doesn't occur in a different model, and so on. I know every Buick of this era will need this part regardless unless it has been sealed in an oxygen-free bag since the day it was purchased. That's what I was getting at.

So I plugged the amp in and fired it up, having only changed the power tubes so far and it sounds, well, as good as this amp will. It's fair but it's certainly not the '64 JTM45 I fixed a while back and I knew it wouldn't be. After doing so the only thing I found to be wrong with it is a dirty/bad drive pot which is simple to clean/fix.

Back when I started working on amps it was part troubleshooting and part looking up the problem to see what someone else fixed. I'm trying to concentrate more on the actual troubleshooting these days BUT it also never hurts to search for another occurrence someone else had to deal with to save time. There are usually lots of hints from you and the others as far as what to look for and why, and the why part is important to me so I'm not just a parts swapper. I detest that guy and don't want to be him.

[gui_tarzan]

I know a few things about Skylarks, they come in metallic mint green, just like a Pontiac GTO, and they are NEVER confused with a Corvette.

Funny story, I have a '64 Skylark that I'm restoring as money allows and one of the neighborhood kids walked by one day when my dad (a 40+ year bodyman) and I were working on it. The kid stops and with big eyes says "whoa, is that a Corvette?"

I just laughed and said no, it's better than a Corvette, it's a Buick!

[Audiotexan]

Aside from the wealth of insight and wisdom in there, and more impressively (to me with my crappy memory), that you somehow *always* manage to maintain at the forefront...

I know a few things about Skylarks, they come in metallic mint green, just like a Pontiac GTO, and they are NEVER confused with a Corvette.

+1 million for the "My Cousin Vinny" reference. ROFL

You're a true gem Enzo. Thanks for being here!

[Tone Meister]

...+1 million for the "My Cousin Vinny" reference. ROFL

You're a true gem Enzo. Thanks for being here!

... ooh you are a smooth talker. You are... you are!

[Enzo]

It's an industry term.

I have a dual-column gas chromatograph, Hewlett-Packard model 5710a with flame analyzing detectors. If you need one:

5710A Gas Chromatograph Hewlett Packard | eBay

[drewl]

I've repaired alot of these.
Aside from some intermittent PC board connections, the many screws that secure the large board have no split washer and come loose often resulting in several problems.
The ribbon cables between boards can become intermittent depending on how much shock the amp receives.
These can be fixed by pushing the wire into the metal pinchers gently when the amp is off and HV discharged.