My BF Deluxe is giving me the blues

Bob Sykes · From: North Carolina

Amp with issues is a '65 Deluxe (not re-issue). Got distorted, smelly and blew fuse on a gig. One of the power tubes looks cooked and its 1W grid resistor was definately toast. I replaced them, ran it (sig gen) on the bench just below clipping for about an hour. No issues. I thought it was fixed and put amp back in cabinet, and played humbucker 6 string loud through it. It seemed to be intermittently losing power and distorting when I hit the low E hard. These were the symptoms right before its demise on the gig so I didn't push my luck.

Now I'm guessing I have some kind of bad connection somewhere in the output section. Possibly vibration related as I didn't have the amp in the cab when I was bench testing. I'll do some tapping around on it to check for intermittents, but if it aint that, I'm not sure how to isolate. Resistors are cheap but I don't want to toast another 6V6. Would loose power tube socket pins cause this?
adTHANKSvance,
Bob
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Gabriel Edell · From: Hamilton, Ontario

Maybe tube socket connections? You can use a thick sewing needle or dental pick to re-tension them.

Also cleaning the tube sockets with WD-40 as per Skip Simmons: Spray some WD-40 into a container of some sort. Then use your finger to apply a light film to the pins of the tubes. Insert and pull the tubes several times.
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Stephen Cowell · From: Round Rock, Texas, USA

Don't use WD-40 on amplifiers unless you're trying to disperse water... that's what it's for.

The proper magic fluid is Caig De-Oxit. Caig makes a good kit for doing tube amps... you need the high-temp stuff if you're going to use it on tube pins. This is the good kit, and this is a good price:

https://www.amplifiedparts.com/products/vacuum-tube-survival-kit-caig-deoxit-gold

Use the red stuff for cleaning, and the gold stuff for preserving. It really is magic stuff.

When you replace final tubes (your 6V6's) replace both, and use a matched pair. Also, check your bias, and run the recommended bias current given to you by the tube manufacturer or vendor. While you're in the amp, re-tense and clean/treat all the connections, and check the screen resistors... you want them within tolerance.

In short, after a bench service, your amp should work fine for a long time. If you aren't well-versed in things like biasing your amp, you'd be better off taking it to a reputable tech... that classic deserves it.
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Steven Paris · From: Los Angeles

Gabriel Edell · From: Hamilton, Ontario

Bob Sykes · From: North Carolina

Thanks for the help guys. I put the amp on the bench and ran it hard while tapping around on the insides. I didn't get a reaction in the power tube neighborhood, but when I tapped on the big blue capacitor closest to them, the output voltage dropped by about one half intermittently. Unfortunately, it stopped acting up and I could not get it misbehave. So I put it together, took it down to the local blues jam and played through it (along with other players) for most of the night without incident.

I don't consider it fixed, and as suggested, I will give it a good going through. Hopefully I can find and correct the intermittent connection then. It would appear to be somewhere near the end of the circuit board.

I've played countless gigs with this amp over the past 30 years and haven't done much to it during that time. I did replace the filter caps and put a grounded line cord on it about 10 years ago. I put an (old) set of matched power tubes in it yesterday, but did not bias them as they are temporary.
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Brian Hollands · From: Geneva, FL USA

That sounds like your culprit. If you didn't do it already, I'd re-solder the joints on those coupling caps.
As Gabriel said, re-tensioning the tube sockets is a good idea too. They got hot and loose pins can cause all sorts of weirdness. I'd check the rectifier pins too.
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'81 Sho-bud LDG, 2 EMCI's

J Fletcher · From: London,Ont,Canada

Hi Bob
You might want to check that the ground leads from the circuit card to the brass grounding plate are all good. I have seen these lift at the brass plate a few times.

Bob Sykes · From: North Carolina

+1 on grounding leads. I learned about that the hard way when my BF Bassman 50 took a tumble (unpowered) from about 3ft. height. Suprizingly it worked afterwards, but I spent a long time tracking down intermittent problems caused by that solder joint which had popped loose but looked fine. I forgot all about that until now Embarassed

Thanks for that and the other good ideas.
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ISO Sustainus Ad Infinitum

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