Help... Real amp cutting in and out

unix-guy

unix-guy

Master of RTFM
Today I pulled my Budda SuperDrive II out of the case for the first time in at least 2 years. Wanted to make sure I was ready to sell...

I plugged in and played (quietly) for a little bit and noticed that the was dropping and coming back... And it started sounding thin and scratchy.

I tried swapping out all the tubes except the rectifier (because the center "pin" cracked off as I was trying to install it :().

After that, I removed all the tubes and the took the chassis out of the cabinet. I visually inspected it and don't see anything apparent.

I reinstalled all the tubes (outside the cabinet) and hooked it up to the speakers. Turned it on and it seemed back to normal. About 20 minutes later the volume dropped again...

Any ideas?

I did also try tapping all the tubes. Nothing changed, no audible effect from that.
 
Sounds like something is intermittently failing when it gets hot. My first suspicion would be that rectifier tube. The fact that it suffered a case break is further evidence that there might be a problem there.
 
Dave Merrill said:
Pots and jacks and switches are the most common things to go intermittent in my experience. Exercise them all a bit.
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This! If your amp was without employment for a long period potmeters might be a major issue.
The soldering idea is right also, I wouldn't hesit to take an iron and just heat up the connections that look suspect.
 
Eurotubes says one of the most neglected, common causes of problems, yet easiest to remedy, is cleaning your tube pins, using something like WD40 Specialist Contact Cleaner, and working the pins into the sockets to make sure the cleaner is evenly distributed, and ensure a solid contact. I'd try that, and also replace the tubes one at a time with a known good tube, as the first step in troubleshooting.
 
Rex said:
Sounds like something is intermittently failing when it gets hot. My first suspicion would be that rectifier tube. The fact that it suffered a case break is further evidence that there might be a problem there.
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The one that's in there is fine, it's the one I tried to use as a replacement that broke.
 
TSJMajesty said:
Eurotubes says one of the most neglected, common causes of problems, yet easiest to remedy, is cleaning your tube pins, using something like WD40 Specialist Contact Cleaner, and working the pins into the sockets to make sure the cleaner is evenly distributed, and ensure a solid contact. I'd try that, and also replace the tubes one at a time with a known good tube, as the first step in troubleshooting.
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I will try that will some contact cleaner I have.

As mentioned in the OP, I replaced all tubes except the rectifier and still had the same problem.
 
Toopy14 said:
I had a similar issue with my AC30. It was a cracked solder joint. The tech. I took it to, used a can of Cold Spary to isolate it.
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I suspect I'll need to find a tech. Last time I required one it was an amp under warranty so I took it where they sent me... But that was maybe 15 years ago :(
 
Ocnor said:
9 times out of 10 that problem is caused by dirty/corroded FX loop jacks. Spray some Deoxit in the jacks and take a cord and plug and unplug it a bunch of times.
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I can definitely do that, too... But there's nothing plugged in. Not sure if that matters?
 
unix-guy said:
I can definitely do that, too... But there's nothing plugged in. Not sure if that matters?
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It could matter. FX-loop jacks usually have extra contacts that close when nothing is plugged in. One of the FX-loop jacks on my Rockmaster was so dodgy that I just kept a permanent jumper in that loop.
 
Toopy14 said:
I had a similar issue with my AC30. It was a cracked solder joint. The tech. I took it to, used a can of Cold Spary to isolate it.
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A cracked solder joint or dirty tube pins make the most sense to me given the symptom that the problem occurs after 20 minutes.

If it was a tube itself it’d immediately act up as soon as power was applied or as soon as it got hot, which would be within a few minutes. If it was a pot it’d make noise or drop out when turned, or would be sticky, but either way would be noticeable right away.

If it’s a bad solder joint or dirty pins the heat won’t immediately affect the connection because it can take a while to spread through the chassis or through the tube sockets. I’d spray deoxit on the pins and in the sockets first, then carefully work the tubes in and out a couple times and see, as that’s a faster job than spraying the solder joints.

It wouldn’t hurt to spray the inside of the pots and jacks too just as a maintenance task. I suspect all our amps and pedals are going to be mothballed indefinitely with Cygnus sounding so good. I really love the sound of my amps and pedal board but the FM3 and FX3… dang!
 
Greg Ferguson said:
A cracked solder joint or dirty tube pins make the most sense to me given the symptom that the problem occurs after 20 minutes.

If it was a tube itself it’d immediately act up as soon as power was applied or as soon as it got hot, which would be within a few minutes. If it was a pot it’d make noise or drop out when turned, or would be sticky, but either way would be noticeable right away.

If it’s a bad solder joint or dirty pins the heat won’t immediately affect the connection because it can take a while to spread through the chassis or through the tube sockets. I’d spray deoxit on the pins and in the sockets first, then carefully work the tubes in and out a couple times and see, as that’s a faster job than spraying the solder joints.

It wouldn’t hurt to spray the inside of the pots and jacks too just as a maintenance task. I suspect all our amps and pedals are going to be mothballed indefinitely with Cygnus sounding so good. I really love the sound of my amps and pedal board but the FM3 and FX3… dang!
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Exact, resolder the tube feet (just melt and take off the iron. Encountered that on a DLR reissue...a long time ago, the time I still had tube amps.
 
lauke-lux said:
Exact, resolder the tube feet (just melt and take off the iron. Encountered that on a DLR reissue...a long time ago, the time I still had tube amps.
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Disagree. If the problem still exists after doing the basic maintenance/troubleshooting techniques that all owners of tube amps should know & do, it's time to let a qualified tech take over (unless you are one, or consider yourself to be one.)
 
TSJMajesty said:
Disagree. If the problem still exists after doing the basic maintenance/troubleshooting techniques that all owners of tube amps should know & do, it's time to let a qualified tech take over (unless you are one, or consider yourself to be one.)
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Correct. There are voltages lurking inside tube amps that can take your breath away. Literally.

A good tech can usually pin-point the problem and fix it quickly.
 
Greg Ferguson said:
Correct. There are voltages lurking inside tube amps that can take your breath away. Literally.

A good tech can usually pin-point the problem and fix it quickly.
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Sure that's the best if you have a tech under the hood close to home. And effectively, you should do those manipulations with power off and concensators decharged....I couldn't imagine otherwise but indeed. In those days 10 years ago I did my power tube replacements and biasing for my 2 main amps then (A Carvin Belair 212 amp and a PV 50/50) but event with an electrical engineering Bsc in hand I sure wouldn't know how to do that anymore today. Well guess @greg is right...better go see a tech if you're not comfortable with electronics, a new amp is more expensive than one hour for a tech.
 
I think I read somewhere some older Buddas were prone to having issues with the tube sockets? Given it takes some operating time to manifest the issue It certainly sounds like a cracked solder or something at a heat generating point ..... but unless there's something obvious to see it's probably best to let an amp tech test it out. What you really don't want to do is keep firing it up to see if it's magically gone ..... because if something major lets go then half the components could go with it.
 
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