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Fender PA 100


isaac42

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Friend of mine has one. Has no real use for it, so He decided to sell it. Placed the ad, lined up a buyer. The day before the buyer was to come pick it up, he turned it on, and a fuse blew. Deal was off.

He asked me what to look for. I told him that the first place to look, in a tube amp, was the power tubes. Replaced them all, fuse still blew. Then I said to check the power supply caps. He said he did, still blowing fuses, so I said maybe it was time I looked at it.

"Oh, by the way," he says, "There's this loose wire. I looked, and there's only one place it could go. I tried that, and it still blew a fuse."

Intriguing. So I got the amp home and took a look at it. I found a shorted power supply cap, which is what I was hoping for. Easy to find, easy to fix, and cheap. If it had been the transformer, it wouldn't have been worth fixing. But that wire...

I looked over the schematic, and the node that the wire was attached to had five connections. All five were properly made. Was there a sixth connection not shown on the schematic? I looked at the spot he thought it should connect to. That location had all of its connections made. Besides, it connected to the grid of a tube. Applying 400 volts to the grid is not usually a good idea.

I was stumped. So I replaced the cap with one I had laying around, and brought it up to full power over several hours. Plugged in a microphone, and it worked. Plugged my bass into all eight inputs, checked the operation of all controls (except the reverb, as I don't have a reverb tank handy). Everything works.

So what is that wire? I have no idea. I taped it off. Damnedest thing.

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IIRC, those are basically a modified SF Twin, in head form, with 8 rather than 4 inputs...I haven't seen one in forty something years....they were a nice 'step up' from the Shure Vocal Master PA of the era which was solid state and rated 100W. I have used both, back in the day, and the Fender, despite the feedback issues, was louder and had a lot  more 'punch' to cut through the mix than the Shure could muster.

They actually are very nice tube amps, but let's be honest, 100W PA systems are not up to the task of competing with powered speakers that can boast over 1200W.

If your friend is still planning to sell it, I doubt he will get much more than ~$400 for it...which isn't bad for a 'vintage' tube head.

 

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