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Old 1st May 2010, 07:16 PM   #1
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Default Help with Paco SA-40

Hello i have aquired a PACO SA-40
its original origins are unknown but the guy i got it from said he thinks a hotal was using it for an intercom/PA system.

It powers on and all the tube elements glow but it starts smoking like its 1970 again. I've traced the smoke to be either an OPT or a capacitor.

I found a schematic here
But i cant quite identify the capacitor.

i circled the two problem children in the photo.
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Old 1st May 2010, 08:20 PM   #2
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That's C3 on the schem. It's a multi-section electrolytic (A,B,C,D) that has seen better days. You'll need to replace it, either with the same values in one "can", or with separate capacitors.

Jeff
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Old 1st May 2010, 08:28 PM   #3
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ahah thanks man. Ill order some up. idk if i can find the can per say but i can probably gut that one. the shell of the can seems to be the common. four leads on the bottom and two bolts to the case. and theres a ground terminal on the case. hopefully these wont cost me an arm and leg but i was starting to freak when i thought it was the OPT
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Old 1st May 2010, 09:05 PM   #4
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You may be forced to buy a 4 x 20uf "twist-lock" plus an 80uf axial. You could use three of the 20uf sections and mount the 80uf axial underneath. I'd also be tempted to replace all the other electrolytic caps in the PS, just to avoid more magic smoke from escaping.

Probably a good idea to check the OPT for shorts just in case.

Jeff
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Old 4th May 2010, 10:12 PM   #5
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hey you were on to something.
JJ makes a can cap thats 40uf x 20uf x 20uf x 20uf at 500 volts
and its only 15 dollars at tube depot.
JJ Can Capacitor 40F x 20F x 20F x 20F / 500V
and a 40uf sprague atom is only 9 dollars.
if i bought them individually it would have been almost 50 dollars after shipping.

-edit-
i know this isnt quite the time to upgrade but alot of people seem to be changing from the 7199's to the 6U8A. it has a different pin out but the rest of the specs are the same.
tube depot also offers triode balancing. according to the schematic one triode from each tube is used in each channel. seems this would be cheaper than buying a matched quad of 12ax7's and has the same outcome wouldnt it?

Last edited by bacon665; 4th May 2010 at 10:16 PM. Reason: added more info
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Old 6th May 2010, 12:19 AM   #6
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Quote:
Originally Posted by bacon665 View Post
i know this isnt quite the time to upgrade but alot of people seem to be changing from the 7199's to the 6U8A. it has a different pin out but the rest of the specs are the same.
I think that's because 7199's are getting more expensive, as NOS supplies run out. There are a few potential alternatives, 6GH8A, 6GJ8, 6EA8, 6LM8. The triode sections seem to have a bit more gain, and watch for different pin-outs and bias of course.

Quote:
Originally Posted by bacon665 View Post
tube depot also offers triode balancing. according to the schematic one triode from each tube is used in each channel. seems this would be cheaper than buying a matched quad of 12ax7's and has the same outcome wouldnt it?
Just bypass the tone controls and get one (1) Jan GE 5751 for the preamp stage, if you need a 12AX7.

Jeff
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