You probably got one with a burnt circuit board or one thats in the process of burning.

A lot of pro jr owners are the same. They tube swap like crazy because they think it’s the in thing to do or whatever, and then they dont bother rebiasing. They just think these things are plug and pray.

Thats why a lot of pro jr’s end up on ebay – what they dont tell you is that they swapped the tubes without rebiasing and for the last couple of years the amp has been cooking itself or it’s tubes. And they’ll tell you it sounds great, and it will. Any amp thats cooking itself to death will sound like a monster until it dies. Thats what you get with cooked tubes.

So my guess is, your 20 dollar pro jr (lol, did I get a great deal – come on dont be dumb) is probably cooked to fuckery. I’d get in there and check it out……check for non standard tubes and then check to see if they did anything about the bias resistor. If you’ve got an aftermarket bunch of tubes and a 15k resistor in r29 (I think it’s r29, might be r28 cant remember) then the tubes were swapped, the bias wasn’t set and the tubes slowly cooked and thats why it’s being sold now.

Dont buy a cooked PJ. Ask questions about tube swap history and rebiasing. If they tell you the amp sounds great and they’ve swapped the tubes with no rebias, it sounds great cos it’s cooking. Dont buy it.

Yep! I paid $240 and $275 for two that I own. Great deal! If yoh want to double your money I’ll give you $40 LOL!

I bought 1 of these amps at a yard sale today,(9/9/18) 4 $20 and it is in good condition and it works.Do ya think I got me a good deal?

If you’re just changing the preamp tube, no bias adjustment is needed. If you’re changing the EL84 output tubes, and the new tubes are bought as “matched pairs” (meaning they have the same gain), then typically no bias adjustment is necessary—and on this model, bias can’t actually be adjusted anyway. However, if the amp sounds dull or cold after the change, your best option is to have the output tubes re-biased. This requires modifying the circuit to make it variable bias instead of fixed bias, which should only be done by an experienced technician at a reputable local shop. Even if you’re just swapping a tube, be careful! You’re dealing with high voltages that can kill you. You’ll be playing a harp in heaven instead of a guitar on earth if you get zapped by the 385+ volts of plate voltage present in the output stage of this amp. Always make sure the amp is turned off and has been unplugged for quite a while before working on it—these power supplies can hold lethal voltage for hours after shutdown. Good luck! —Mendamp

When changing pre-amp and power tubes, must the new tubes be biased?