Friendly Safety Announcement for Peavey Classic amps

[lars]

I've been tinkering around with a Peavey Classic 20 that I got for cheap, trying out different mods and such. One thing I noticed is that on the available schematics it doesn't show anything having to do with the 120v side of the power transformer (it doesn't show the power switch, main fuse, pilot lite). I guess that's because they didn't want people to know the completely idiotic thing they did. If you have a Peavey Classic-series amp, I would immediately check this to make sure you don't possibly kill yourself. Look at this:

What you're looking at there is a true "death cap". Peavey chose the wrong type of safety capacitor for the 120v hot lead to ground. An "X2" rated capacitor, like the one pictured, is an "across the line" capacitor. It is designed to fail closed in a short situation. So it doesn't take a genius to figure out what happens if it fails installed in that position. It will send 120v AC directly into the chassis, and if you're not hooked up to a properly-grounded wall receptacle, that also means into YOU since the input jack is grounded to the chassis! They should have used a "Y2" rated capacitor, which is designed to fail open and is specifically for line to ground situations. I would recommend immediately removing this capacitor if you have a Classic 20 or 30 or 50 (I'm guessing they all have this bonus bonehead feature).

[cooder]

Good one for Death Metal.... ouch...

[HamSandwich]

Holy hell! Thank you. I've been playing a classic 30 for 10 years now. Maybe I'll give her a good moding in there while it's open. Any tips?

[cooder]

Holy hell! Thank you. I've been playing a classic 30 for 10 years now. Maybe I'll give her a good moding in there while it's open. Any tips?

First tip: they are a royal PITA to work on due to their interconnected pcbs and build architecture. Ask any repairman who has had their fingers in them. Prepare to hear swear words.

[lars]

First tip: they are a royal PITA to work on due to their interconnected pcbs and build architecture.

You are correct, sir. It is a pain.

My biggest suggestions for Peavey classics:
1) Get rid of the death cap if it's there. Also, you can get rid of the "anti-switch pop" cap that is soldered in right next to the death cap. Neither one of them make a stitch of difference on the noise, and I've actually found my switch doesn't pop anymore with the cap not installed. 
2) Change the horrible 3/4" MDF baffle board for a proper 3/8" high-quality plywood board (this is more effective than a speaker change - you will like the stock speaker after this)
3) Change the "extension speaker" jack to an isolated plastic jack. Peavey screwed up this one. By using a metal jack that is grounded to the chassis, they provide and alternate path to ground that messes up the entire elevated ground scheme they were going for and actually makes a ground loop - not good. Apparently the noise gets worse when the extension speaker jack isn't grounded. At this point, I don't know what to make of their grounding scheme. The schematic shows it's wrong. The implementation is wrong. I guess just keep trying different things to find which one is the least noisy.
4) Ground that flux band on the power transformer for crying out loud! Peavey screwed up there as well by going through all that trouble to put on a flux band...but then not grounding it! And speaking of the power transformer....
5) Isolate three of the mounting bolts that hold the power transformer to the chassis so that the core only grounds through one bolt. Power transformer cores are not supposed to have multiple paths to ground, but pretty much every manufacturer grounds their transformer core in four locations through the mounting bolts (the more you know).

[gordo]

+1 on repairs.  The only amps that are more of a PITA to work on are the smaller Egnators (I quit working on them) and JCM600's (no, I hadn't heard of them either till I had to rework a few...that's why they're so rare).

[lars]

Just saw a picture of the inside of a JCM600. If that wasn't done on purpose to discourage servicing the amp, then somebody has some serious spatial recognition issues. It looks like the type of person who tried to put a hexagonal peg into a rhombus hole.

[gordo]

...rhombus hole...ha!  I like that.

[imjonwain]

Oh man, that JCM600 inside is nuts.  My old boss was obsessed with making our systems smaller even when there was no reason too and electronics + software just "happened" to him.  We definitely built stuff I hated repairing and assembling.  Thanks for the Peavey tip.

[danfrank]

Yes, most all if not all Peavey amps have these caps across the line voltage. First thing I do when one of these amps comes in is remove those two caps you took a pic of. Because these amps have a grounded plug (3 prong) those two cPs don't serve a purpose. TAKE THEM OUT! Lol!
As for the 600 and others, many times the engineers don't even consider that the amp may need to be worked on at a later date, they're oblivious. Their main concern it that it gets assembled in an efficient and inexpensive way.

[lars]

Yes, most all if not all Peavey amps have these caps across the line voltage.

And just to reiterate, the main problem is that Peavey chose the wrong type of capacitor for it's line to ground application. You can use line to ground caps all day, as long as they are "Y"-rated capacitors. Look inside any Furman Power Conditioner, and you will find them there. So most of us use "death caps" all the time, without even realizing it. But an "X"-rated capacitor is wrong, wrong, wrong, to use to ground. It will fail short, and send voltage into the chassis.

Oh man, that JCM600 inside is nuts. 

On the flip side of the Marshall coin, take a look at the inside of an AST1H. Absolutely beautiful circuit board in there.