Peavey Series 100 Classic 50W 2x12 No Output

[misterc57]

Just picked up this amp and starting to go though it. Was told it powers up and it has no output. Have not powered it up yet.

Filter caps were replaced and looks like a 3 prong cord installed.

Speaker cable reads 7.7 ohms.

It has a pair of barely good 6L6GC M.I.China Ruby power tubes. These tubes look very cooked. Oddly each has a diode from pin 3 to pin 8 (cathode to anode), why???

I'm looking things over and will turn on soon and take readings on the power tube pins.

I think this is the schematic.

Any thought? Thank you!

Peavey_Classic_(A_Series)_Schematics.pdf

[TomCarlos]

I think this is the schematic.

Any thought? Thank you!

Please post a photo of the front panel. That will tell us if you have a Version A, or Version B, or something in-between. (I have posts here on MEF related to this amp - I will point you to them if needed).

The close up photo of the tube sockets looks like you have burned pins. But the far away view looks ok.

Before you take voltage readings, pull the output tubes.

It looks like this amp has undergone a partial cap job. So start with the power supply. Double check the values of the caps and dropping resistors. Do I see one of the resistors as having burn marks?

Start with reading for the power supply section and the bias voltage. (Again, I can point you to a post where the MEF members helped me redo the bias section if you decide to make some mods).

And it looks like there is lots of rust or oxidation on the jacks and connectors? Make sure all connections to ground and the chassis are clean.

Tom

[The Dude]

The diodes from plate to ground are snubbers to protect the OT among other things. I'd just leave them alone, unless they are shorted.

[TomCarlos]

If you have the snubber diodes, you probably have a Classic B version.

Peavey_Classic_B_Schematic.pdf

And it turns out, there was something between Version A and B that was not properly documented by Peavey. I call it the Classic A Plus Version. The schematic below depict this release. I am also showing the BIAS mod that MEF members designed on the A Plus Power Amp schematic. I drilled some small holes in the PCB to accommodate moving and adding parts.

Peavey_Classic_A_ Plus_Power.pdf

Peavey_Classic_A_Plus_Preamp.pdf

[Jon Snell]

Without powering it up and no report of a fault, what can we suggest ...
Put in the correct value main smoothing capacitors and make the wiring suitable for use, not components hanging in mid air with insulation burnt off wires. That is a recipe for dissaster at a gig.

The photos are very dark, lacking detail but I wouldn't say the valve holders were burnt.
There is a rubber grommet missing where the reverb pan is connected.

Let us know what results you get when powered up.

By the way, the correct function of the 'snubber diodes' is to help clip the high voltages generated when there is no loudspeaker load attached and powered on with signal, (back EMF from an open circuit transformer)..

[Stratfordade]

I have a similar but not identical Peavey awaiting restoration. All I’ve done on it so far is get the original blown OT rewound. This just reminds me to suggest checking OT before diving into detailed stuff, but based on no diagnostic info other than “no output”.

Note if you do require a new OT the original layout had no room for substitute without a lot of modifications, hence had original rewound.

[DrGonz78]

Well I would inspect the two twisted green wires running between the two mains filter caps. Those are your filament voltage wires and they are sitting right on top of a very hot B+ dropping resistor. Zoomed in on that part of the image I have to question whether or not the wiring has been compromised. I can almost see blackness and heat damage on your filament wires right where it seems to be touching that cement dropping resistor. I would make it a point to check that wiring and move it away from hot resistors. Also the wiring of those filter caps looks pretty ugly even on a nice day. So I would clean up that stuff too.

[misterc57]

Thanks for all the great info. Glad I asked.

Transformers test good. Not sure OT is original.

With no tubes installed seeing +500V at both pins 4, but only one pin 3, if I lift the stub diode I see the +500V. -58V both pin 5.

Replaced the one bad diode with a 1n4003. Assumed a general purpose diode is okay?

Installed the tubes that had come with it. Not liking these tubes. They are really loose in their black base, can be twisted and tilted like the tower of Pisa.

Powered up slow, current looks good. No noise. Plug in a guitar. Have sound, all function responding, then a hum creeps in becomes loud, see my current meter is pegged, see smoke coming out the back side near the filter cap area.

Shut down.

Def. been some smoke shows before in this amp, can see traces all over the chassis.

Not sure what was burning. caps and resistors all look good although I cannot get a good read on the 68K 1W filter cap.

I am very suspicious of the tubes. maybe they are shorting after warming up.

I think the burn marks on the filament wires and other wires are from soldering iron.

I am assuming the B version schematic for now. Def. some cleanup work to be done if I think it is worth it.

Thank you

Peavey_Classic_B_Schematic.pdf

[TomCarlos]

If this helps give you some ideas, here is how I replaced the caps in the Power Supply section. For the 60uf cap, I had two 30uf caps - so I put them in parallel.

[The Dude]

......Replaced the one bad diode with a 1n4003. Assumed a general purpose diode is okay?......

Which diode did you replace? If you're talking about one of the snubbers, no it's not ok. A 1N4003 is not rated high enough for that application.

[mozz]

I admit i rip those diodes out on any Fender of that era. May not be the thing to do but never had a amp come back due to that. You can remove them and then wait until you get the proper ones, if you want. I'd be ripping those sockets out and installing new ones (if it was my amp and not a customers). Looks like a mess and the caps and wiring needs a redo.

[DrGonz78]

I wouldn’t power it up until I gave the amp a full inspection and even from a picture it’s that obvious. This is your life don’t gamble on shotty wiring. I still can’t get over the placement of the filament wires. You need a variac and ammeter to power up questionable equipment. Even then I would have redone that messed up wiring before even bothering with such a gamble.

[Jon Snell]

Those diodes must be similar to R3000 (3kv 150mA) or RGP02-20E 2kv type. Mouser supply the latter, others are obsolete.
https://www.mouser.co.uk/ProductDeta...XU1CCUqNc9Q1d9

I would suspect the vlves firstly but only if you are suitably qualified, otherwise, leave it for a professional (your level of questioning is not very advanced), before you hurt yourself.

[misterc57]

Dang. I have never seen a snubber diode on a tube plate before and I thought that SR2873 was a PV part number and went with "all diodes 1A 200V..."

Components were face down on the bench and I'm thinkin it was the 1n4003 that was starting to cook as it looks a little wonky but still tests ok. I'm thinking of lifting both snubs off the plate and re-test, components face up.

Appreciate the concerns. I'm running a variac with a amp meter. I'm very careful and have inspected numerous times visually and with meter for issues before powering up. I drain high voltage and keep it shorted during all soldering or repairs.

This is my amp I bought on the cheap. Once working I will invest into the proper rework.

Thank you

[misterc57]

Progress.

Installed different set of sacrificial 6L6GC tubes. Snubs lifted, amp turned on for quite a while. no smoke, got sound... constant 0.6A current at the variac.

Following DC V readings at the tube pins

pin 3 462
pin 4 461
pin 5 -54

pin 3 466
pin 4 462
pin 5 -55

I'm considering leaving snubs off. Thoughts?

Amp is connected to my bench 8 ohm speaker cab. I'm not caring for the sound, have only tried the normal channel. Very gritty sounding.

Thank you