What is the first action you would take here?

Exhead

Exhead

Member
Bought a 1965 Gibson Vanguard GA 77 RET from an Estate sale. Obviously the guy liked to tweak stuff he owned. I have not even plugged it in yet. What is the first course of action for this to make sure I do not mess it up?

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Pull all the tubes, turn it on plugged into a Variac. Bring voltage up slowly starting at 10 volts then 10 more volts per hour. When you get to 117 volts, turn it off, put the tubes back in, and rock it. Assuming it didn’t pop any fuses or catch fire or anything.
 
I’d open it up and do a visual check. If he liked to tweak things it might not be finished or ready/safe to fire up. Not sure if that amp falls into the ungrounded plug era or not. If so I’d add some grounding for your own safety.
 
paulyc said:
Pull all the tubes, turn it on plugged into a Variac. Bring voltage up slowly starting at 10 volts then 10 more volts per hour. When you get to 117 volts, turn it off, put the tubes back in, and rock it. Assuming it didn’t pop any fuses or catch fire or anything.
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This is wrong.

Don’t ever go to full working voltage on a vintage amp with all tubes pulled. You run the risk of over voltage filter caps since no tubes are pulling the B+ down.

I’d open it up and follow the circuit with a continuity meter from B+ to ground and make sure it doesn’t beep. If it does you’re in trouble before you even turn it on.

I’d verify no leaking caps visually and see if there’s anything unfinished as said earlier.

I’d check for loose components or anything in the chassis. If he tweaked he probably could have left something in it by accident.

Do use a variac to turn it on and I’d turn it on monitoring the tube bias on the power side carefully looking for runaway.

If it doesn’t have a grounded cord I’d install one first before doing anything at all.
 
Chubbs said:
I’d open it up and do a visual check. If he liked to tweak things it might not be finished or ready/safe to fire up. Not sure if that amp falls into the ungrounded plug era or not. If so I’d add some grounding for your own safety.
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It was connected to effects as if it was in use but I'd like to make sure I don't harm it. Ordered a Variac and will kick it on with tubes removed as suggested here.
 
glpg80 said:
This is wrong.

Don’t ever go to full working voltage on a vintage amp with all tubes pulled. You run the risk of over voltage filter caps since no tubes are pulling the B+ down.

I’d open it up and follow the circuit with a continuity meter from B+ to ground and make sure it doesn’t beep. If it does you’re in trouble before you even turn it on.

I’d verify no leaking caps visually and see if there’s anything unfinished as said earlier.

I’d check for loose components or anything in the chassis. If he tweaked he probably could have left something in it by accident.

Do use a variac to turn it on and I’d turn it on monitoring the tube bias on the power side carefully looking for runaway.

If it doesn’t have a grounded cord I’d install one first before doing anything at all.
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With the Variac down on voltage how can the bias be over voltage ? The bias wouldn’t get near over voltage until it’s up near 110-117 volts, no ? Or it shouldn’t (in theory anyway).
 
paulyc said:
With the Variac down on voltage how can the bias be over voltage ? The bias wouldn’t get near over voltage until it’s up near 110-117 volts, no ? Or it shouldn’t (in theory anyway).
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The tubes can run away if there is a lack of bias regardless of variac setting. They’ll pull B+ down to ground and by the time you’ve realized what’s happened it’s already too late. They’re trying to act as constant current sources.

Also you assume the tubes in it are in working order which isn’t a valid assumption unless they’ve been tested externally. I also wouldn’t put known working new tubes in an unknown questionable circuit unless you’re just made of money.
 
psychodave said:
I see that stock filter cap strapped to the chassis. That fucker looks original… which would be my concern.

Line 6 speakers. lol

What’s that stuff in the bottom?
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There is the original pedal, power cord and it has an oil can reverb which is so vintage I have never seen it before.

Will provide more pics when I get to this one. I picked up about 8 amps from this estate sale.
 
Exhead said:
It was connected to effects as if it was in use but I'd like to make sure I don't harm it. Ordered a Variac and will kick it on with tubes removed as suggested here.
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Just saw this as my notifications are fucky.

The variac is a good idea but starting the amp up without tubes probably isn’t a great idea as your caps we’re probably rated for 500v 50 years ago and judging from the one pic they’re likely still the stock caps. Even if it did fire up your probably going to be close to the limit with tubes in. I’d at a minimum open it up and look to see if they’re original or not, if they are I’d spend the $30 or so on new caps. It’s peace of mind and would save hours of cleaning.
Also check the speaker impedance, just to make sure you aren’t running a huge mismatch.
 
Yeah, those L6 speakers gotta go. But after you verify the amp is working. It wouldn’t be fair to try and evaluate the sound with those things in there.
 
The amp works, one of the 6L6 tubes does not work, I will have to replace it. As a result it is low sound. The oil can reverb pulley works, the fan works, not sure if there is oil in the oil can. I think I will just sell it for a fair price and let someone else do all the work on it who knows way more about amps than I do. I know close to nothing.
 
Exhead said:
The amp works, one of the 6L6 tubes does not work, I will have to replace it. As a result it is low sound. The oil can reverb pulley works, the fan works, not sure if there is oil in the oil can. I think I will just sell it for a fair price and let someone else do all the work on it who knows way more about amps than I do. I know close to nothing.
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I think it’s a good idea to let it go. I wouldn’t want to go poking around without knowing what’s what either.
 
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