Broken Fender Bassman 135?

[Kügel]

So here's the deal.

A few months back I bought a '78 Fender Bassman 135. It had been completely been cleaned up and set-up nicely in the shop and was in perfect order.

I took it home, played it a bit but mostly kept on playing my practice amp so I don't cause too much noise for the people living here, and was going to use the amp on our next upcoming gigs.

The gigs there and I take the amp with me, and about halfway through something happens. I don't know exactly what but there's white smoke coming out of the amp and my bass sound is gone.

I heard that someone got on the stage and accidently pulled out the plug from my amp, then tried to put it back in but stuck it somewhere completely wrong which caused a shortcut.

I had a friend come over who's very knowledgeable about old amps to check it out.

At first we tought it were the tubes, so I bought new ones but that didn't fix a thing. Then we found a blown capacitor which we replaced. Still no change.

The tubes heat up but that's it. My volumes turned up, everything looks a-ok and working but still there's no sound.

Any suggestions on what it might be? I'm really bummed that it's still broken

 

[Martin C]

hi i guess the problem is the transformer
it needs to be changed
it happends when you unplug the plug that connects de amp from the cabinet

sory for my english i´m from argentina
good luck whith it!

 

[RickenBoogie]

Which plug? If it was the mains power, that shouldn't have caused too much trouble. If it were the speaker cable, and it was plugged back into something other than the speaker out, you may very well have fried the transformer. Bummer. Don't let anyone near the back of your bass rig,...ever. Take it in to a qualified amp tech, they can diagnois the prob, and fix it.

 

[christw]

Output transformer is toast probably. Plugged into the wrong impedance... it'll roast.

 

[Kügel]

Alright thanks for the replies.
Anyone know where I can find a transformer in Europe?

Or a qualified amp tech for that matter...

 

[throbbinnut]

Do you know which capacitor was fried? You may have fried a power resistor in the power supply. Can't tell without looking at it. Find somebody with a voltmeter so they can check it out internally.

Chris

 

[Kügel]

Yeah we checked out most of the parts with a voltmeter and everything seemed perfectly fine.

I'll try to make some pics tomorrow. Not quite sure where the camera is right now.

 

[jimbilly]

Yeah, running a tube amp with no load will kill the output transformer, I think they arc interally (which would explain the smoke). I'm afraid they're generally not very cheap. I wonder if you could find one out of an old organ amplifier?, maybe try to find an organ repair shop near you, that might be good and cheap. Otherwise, MercuryMagnetics makes big claims about theirs, but those are pretty expensive.

 

[coreyfyfe]

I'd agree it sounds like the OT if it was a speaker cable unplugged and plugged into the wrong spot.

Definitely bring it to a tech, I'm sure you can find one. As far as a replacement if it is the OT, these guys are in Germany (as far as I can tell) and have the part:

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[Rattman]

Output transformer is toast probably. Plugged into the wrong impedance... it'll roast.

Yeah... this resounds with me as well.. Had a transformer fry itself one day on a Peavey combo amp. Power light would come on etc.. but NO output at all. The transformer was the culprit, and once replaced everything was plenty loud again. I believe also your impedance load was incorrect.. sorry, but someone goofed up your amp it would appear.

 

[BassmanPaul]

A transformer is a pretty hefty item. I'd guess that it's not toast. You do have to take your amp to a tech. If your knowledgeable friend, no disrespect intended, knew enough about tube amps then you would already know what the problem is. Don't make matters worse by trying to fix the thing yourself.

Paul

 

[Kügel]

Yeah, he knows a bit but he doesn't know all. I can't blame him, he did his best and I'm very grateful for that.

I'm going to try and find a good tech around these parts and have it looked at.

The cost wouldn't matter that much since I know the person who did it and she said she was going to pay me for the costs I have.

 

[wingsken]

Im the guy who checked it out. What happened was a short circuited preamp (well thats what i could make out of what they both told me.) I found a loose capacitor on the poweramp filter which i re-attached, then i found a blown up cap under the pan (one of the caps on the feed line to the tubes ( 50µF 500V theres 3 of these ) so i replaced that. Note that i checked all resistors with a multimeter and they all checked ok. Thinking that the outputr transformer is broken is jumping to conclusions, there hasnt been a false load attached to it. i didnt really have the time yet to take it home and take it apart. it will probably be a false phaseshifter tube. But ill let u know what the problem was when i find out. Fender amps are easy when they are in the right enviroment and someone elses garage isnt the real place to repair amps