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Occasional loud popping noise

Broken record: Any valve tester might show a short, but they are useless for testing 5R4 rectifiers and other power valves. I was quite shocked at the really low AC voltage, around 60 Volts, my Hickok 800A and my TV-7/D put on the anodes of these, 807s, and other power valves, and both testers are working correctly, as are yours, probably.

Best test is to plug in a new set of valves to eliminate them as the source of the arcing sound. (I would have a look at the original resistors, though, and re-flow all solder joints.)
 
Carburetor brush kit. Amazon or Ebay. Saw a youtube video of someone using them for cleaning tube sockets. Just google carburetor brush kit.
 
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Lavane said:
Is the pop coming from both speakers, or just one?
Common issues with pops I've come across were caused by various issues.
It can be cauaed by failing capacitor, a failing rectifier, driver or power tube, and even from cold or cracked solder joints.
In one of my amps it was the voltage gain driver tube failing. One section of the dual triode was having intermittent shorts and arcing. I even saw a flash happen inside that tube.
In one of my mono blocks I would get intermittent pops mostly at start up. It took me awhile to find the problem until one day I saw a small flash through a vent slot on top of the amp. It turned out to be a crack in a star ground solder joint. I didn't notice it before even with a magnifier. With the bottom off and lights out I turned the amp on with the bottom off and saw the small arc.
In yet another amp it was the power tube arcing internally.
The tubes that were failing caused a pop in one channel only, where as the bad ground solder joint caused a pop in both channels.
It could be a failing cap too though, or maybe even a bad resistor.
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This^^^^
 
Here's something I've gotten burned by. When replacing components on terminal strips, sometimes the solder drips down to where it's almost shorting to the chassis. With high voltage, especially 900V, I'd check that. It could be close enough to arc.
 
arts said:
Check all of the tube sockets for arcing, especially the rectifiers.
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:thumbsup:

Carbon tracings on sockets or circuit boards from previous shorts. They can be hard to see — dark brown or black serpentine lines. They have to be cleaned up, or the unit may always have a funky reliability issue.

If the socket shows obvious damage from the short, I usually replace it.
 
Back on this tonight, I have to wonder what is worse, having big amps to power inefficient speakers or having flea power amps but having to have huge efficient speakers. Anyhow ran it for a bit and old faithful starts popping, Pulled the plug and rolled it on its side to pull the bottom off. This isn't a barn find, these are ex NASA amps not molested or rusty. But I went back to my work and pulled a cap that the solder connection seemed iffy. It was the .22uF cap on V1 of the 12AX7 pin 6 and the pin 4 of V2 6SN7 I think it is a coupling cap. Also reworked the 5 ohm 50 watt resistor mounting using some clamps connected to the protruding bolts off a transformer. That resistor used to reside on a back wall above the chassis and above and behind the rectifier tubes, but since I removed that divider so the amp is open to the back as since I have a clear front panel I wanted a clear view of the back row of tubes.


Anyhow I don't want to jinx myself but so far, it has been quiet. That one left 811-3 tube looks a bit different on the bottom than the one on the right hope it wasn't damaged by what ever was going on. Anyone I haven't put the bottom plate on just running it on its side. Drawing says that on pin 6 side of the cap I should have 180 volts, but I am getting 220 so I have an issue that I need to figure out.

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high voltage at a plate connection generally means the tube is tired and not pulling enough current, but could also be other tubes not pulling enough current to load down the power supply. Cathode voltage is usually a clue. If its low while the plate is high, the tube isn't pulling as much current. If both are high, the power supply is probably high too. Off-value cathode resistor is also a possibility
 
The voltage is expected to be somewhat higher because of difference in line voltages these days, 125V vs 115V, but 40 volts difference does seem somewhat high but you are dealing with some very high voltages in that amplifier. If you have a variac run the amp at 115V and check voltage.
 
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