Any Musical equipment/electronic guru's???

[Stangman]

Anyone on here technically inclined when it comes to electronics repair regarding musical equipment??

I've got a full tube Peavey Penta guitar amp. Has 8 tubes. 4 EL34's 4 12AX7's.

My buddy owned this thing first and its seen lots of shows and playing. It popped a fuse on him one day, replaced fuse, then popped a power tube. Replaced it and then it quit again. Sold it to me dirt cheap. I found out it needed a non visible fuse that was located on the main board. Replaced it and now it works... well sorta. I started to turn up the volume to test it after I soldered the fuse in, and popped the main fuse. (The first one my friend popped)

Question is.... what could be causing this?

Tubes all lit up prior to popping the main 6a fuse this last time.

Someone told me it could be one of the finals? What's a final? Can I test them? Can I replace them?

Id love to get this thing going again.... its a 140 watt head!

[04 Venom]

Usually with tube amps, when the main fuse blows you look to a power supply capacitor, rectifier diode or a blown output tube. If it blew the main fuse right away, you would suspect the rectifier or power supply cap. If it the fuse blew after the amp had been on a short time, you would suspect one of the El 34 output tubes.

The tubes are available mail order from multiple sources. The best buy for El 34s is Antique Electronics in Tempe, AZ. They sell matched quads of Valve Art EL 34B tubes for $48.00.

[Stangman]

It was on, I let the tubes warm up with the amp on standby for a bit, the volume has the ability to go to 11, but id say I had it on 2 or3, then as soon as I went to turn it halfway up.... pop!

[04 Venom]

It's difficult to definitely diagnose this remotely, but my guess is a bad EL 34. The amp probably runs push-pull parrallel (two output tubes cover the positive phase of the AC signal and 2 output tubes cover the negative phase); to find whether one of the tubes is bad, remove just one tube at a time and then turn the amp on. If the fuse doesn't blow when a particular combination of three tubes are operating, you have identified the bad tube.

[Stangman]

So your saying, try to turn the volume up with a tube out, and if it doesn't pop the main fuse then I've found the culprit (the removed tube).... did I read that correctly?

And, I can have a bad tube even if they light up?

This stuff is all new to me, so I apologize for my ignorance on the subject

[04 Venom]

Correct; if the fuse doesn't pop, you have found the bad tube.

Even if the tube lights up, it can still be bad.

[Stangman]

Got ya. I always thought that if it lit up, that it was good. Thanks for the tip. Looks like I should buy about 5 fuses tonight since I have a one in four chance!

[Stangman]

Thank you 04 Venom. I bought a pack of fuses on my way home.... popped one in. Took out an el34, the first one actually. Powered it on.... turned up the volume and it works great! Just need to replace one tube. Thank goodness!

Thanks again for your help!

[Chunk94GT]

Thank you 04 Venom. I bought a pack of fuses on my way home.... popped one in. Took out an el34, the first one actually. Powered it on.... turned up the volume and it works great! Just need to replace one tube. Thank goodness!

Thanks again for your help!

From back when I play alot of music, its a bad idea to replace just one fuse. If you are replacing the El's it best to replace all with matching tubes also the the same with the smaller ones also. I had a good friend that did alot of tech work for me and I remember him telling me that either do them all or none.