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Old 4th February 2003, 02:07 AM   #1
diyAudio Member
Join Date: Feb 2003
Location: Baton Rouge, LA
Default Old Valco Amp Tube Problem

bought an old Valco-made Class A tube amp over the internet. It has 4 12ax7's, 1 6y6, and 1 5y3. The 5y3's nub was missing. When I first plugged in the tubes, the 12ax7's lit up, but the 6y6 and 5y3 did not. I messed around with readjusting the 5y3 and then none of the tubes lit up. I emailed the previous owner and he explained the exact placement for the 5y3 but still none of the tubes light.

My question is: is it possible that by incorrectly inserting the 5y3 that I blew something that would make none of the tubes light?

I opened it up but I couldn't see anything wrong. Not that I
really know what I am looking for.

The power light to the amp turns on.

I apologize for posting this here but I have been doing research all morning and I find nothing that gives me the answer and there are some very knowledgable people here.

Thanks, Bert
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Old 4th February 2003, 02:38 AM   #2
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Join Date: Dec 2006
Default Danger!!


I opened it up but I couldn't see anything wrong. Not that I really know what I am looking for.
I am new (sort of) and I must say that the voltages are lethal inside most, if not all amplifiers. Please be very careful, the capacitors can hold voltages for quite some time and can zap you.

If your not sure what you are doing, try to find someone that lives by you and can help you. There are a lot of guys that work on guitar tube amps and that is a place to start.

Do you have a schematic? That would be nice but maybe not nescessary. Do you have a DMM tester? (digital multi meter)

The DMM could be used to check the filament wires on the 5y3's by checking continuity. If the filament is bad, ( broken, burned out) then a new/working 5y3 should be installed. Pins 2 and 8 are the filament heater wires

Could be a resistor has fried and again a DMM is handy.

Also having a tube tester is real handy for tube gear, but some times can be expensive to purchase.

There are more experienced members here and if you stick here, you'll figure it out.
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Old 4th February 2003, 12:38 PM   #3
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Join Date: Aug 2002
Location: Belgium
Default VALCO


work on guitar tube amps and that is a place to start.
This is a guitar amp,isn't it?

Do you have the complete name of that model?

There may be a library on the net that has the circuit diagram.

From what I found so far it contains a fair bit of idiosyncracies.

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