Peavey Classic 30 complaint and my idea on how to fix it.

[Dave]

Hey fellows,


I have a Classic 30 that a man dropped off. He said that it runs too hot and smells bad. I took one look at it and noticed that he had a 16ohm resistor across the speaker leads. I asked him about that and he said that that is the way he uses it. He said he never uses a speaker and plays shows at clubs and casinos and plugs the "Ext. Speaker" out into the house sound system. He says he wants that to stay the same, because that is how he uses it.


So, I opened up the amp, and sure enough, it gets very hot on the circuit board right above the power tubes. I measured it at about 185 degrees on the board in the neighborhood of the power tubes and there is some visible signs of high heat conditions.


The amp is working correctly and the bias is about what it is supposed to be. So here are my thoughts.....


When you plug anything into the ext. speaker jack hole, it activates the 8 ohm tap on the output transformer. So, immediately, the 16 ohm resistor across the speaker leads becomes a mismatch. So, the easy answer is PULL TWO TUBES. That solves the impedance mismatch, and half as many tubes creates significantly less heat. Sounds like a winner. But....


I have no idea what kind of load is being presented to the amp by plugging the ext. speaker into the house sound system. So, my only concern is... is there a chance that somehow the house sound system was making the amp behave itself, and would pulling two tubes somehow disrupt that situation?


Please advise,


Dave

[tubeswell]

Well for a start, the output tube heaters in a Classic 30 are wired in series, so if you pull two tubes out, the other tubes won't work.


There is a mod that you can do if you have a pair of EL84s you don't want anymore - where you chop the plate, cathode and screen pins right off with a wire cutter - so that you can keep the tubes plugged in so the heaters will work. The OT reflected load would need to be doubled.


If the boards have heat damage, then personally I'd tell the guy it was time to buy a new amp. Those things are a real PITA to try and fix.

[66Strat]

Return the amp as is. There is no upside to this job. When the amp fails, the "customer" will be at your doorstep demanding that you repair the amp that you "flubbed up".

[Dave]

Thanks Tubeswell for pointing out the series heater wiring. I figure the impedance problem will take care of itself by removing the two tubes. And I couldn't agree more about them being a PITA. Just looking at the way the circuit boards are designed gives me a headache.


66Strat, you win the prize for the soundest piece of advice ever given. I'm going to give that some thought. I usually like to fix something if someone asks me to, but this one seems like a scab that needs to be left alone.


Dave

[shooter]

66Strat, you win the prize for the soundest piece of advice ever given

ask how he knows 

I quit doin PCB amps awhile back, there is NO upside, I know, I've tore into enough to prove it 
On the rare occasion, I stipulate up front the terms and expectations

[Dave]

So, after careful consideration, I opted to fix the guys amp anyway. I am now running the amp with two power tubes waiting to see how hot it gets. I explained to him that based on his unorthodox use of the amplifier, I could not be held responsible for what might happen to the house sound system.


Dave

[labb]

This is what you call real amp abuse. I have run some of the small single ended amps, 5 watts or less,  with out the speaker with a resistor and run the output into another amp..Works pretty good. But 30 watts, I don't see how the amp has lasted very long. Shame, I really like the Classic line of amps from Peavey. Had an old Classic 50 that I paid $100 for at a pawn shop years ago. Son let it get away when he took it off to College. Those old Peavey boys over there in Mississippi are pleasant to deal with. Very helpful.

[Latole]

So, after careful consideration, I opted to fix the guys amp anyway. I am now running the amp with two power tubes waiting to see how hot it gets. I explained to him that based on his unorthodox use of the amplifier, I could not be held responsible for what might happen to the house sound system.


Dave

What mod do you do ? Put heater in parallel or put 2 old EL84 as tubewell wrote ?

I had one Classic 30 few year ago and it is one of the most bad designed amps to fix.

[Dave]

I wound up cutting all the pins except for 4 and 5 on two worn out el84's and installing them, but I didn't like that method. So, I have just about decided to not do anything.


Dave

[Ed_Chambley]

Here is a nice thread for a load box.  Different folks have differing opinions on using these, but better this than what he has. 


https://www.thegearpage.net/board/index.php?threads/aikens-reactive-dummy-load.1072793/

[labb]

Garnet amps come to mind with this type of operation. Not so much as imputing to a sound system but into another amp. might do a little digging in to them and see what they were doing.

[Dave]

Well, I'm kind of done with this "repair" operation, but I did have a look at those Garnet amps and found the one you are speaking of. It looks very interesting for a separate "for me" kind of thing.


Dave

[mresistor]

After looking at picture #2  I thought "wth were they thinking?"   I wouldn't work on one either.    Convert if possible but that's it for me. Even then looks like you might need a new chassis .


http://www.bustedgear.com/repair_Peavey_classic_2.html

[tubeswell]

I wound up cutting all the pins except for 4 and 5 on two worn out el84's and installing them, but I didn't like that method. So, I have just about decided to not do anything.


Dave

Good call. I hate working on these amps


FWIW, if you're going to chop the pins off, then it's better to leave Pins 1, 6 and 8 uncut (alongside the heater pins) - to help provide more mechanical stability seating the tube in the socket. These pins have no electrical function in the circuit. You just have to be careful how you plug the tubes in.