Popping Sound on new build

[azcreamery]

I just finished my Trainwreck build and it sounds great, except that I am getting a popping sound. The sound occurs only after the amp is turned on for about 3 minuites and once the popping starts, it occurs at about 10 second intervals. It occurs even if nothing is pluged into the input jack. So far I have:
-checked for loose pins on tube sockets
-swithched all tubes for know good ones.
-re-soldered all conections and triple checked for cold solder points.
-using chop sticks I can't trigger the popping, it seems to be random at about once every 10 seconds.
-turned out the lights and could not see any arching.

I'm new to building amps, this is my second, and would appreciate any suggestions on solving this.

[Phil_S]

In this order, look for a bad:
1-filter cap
2-coupling cap
3-resistor

[CaseyJones]

Filter caps are a good place to start. Clip your multimeter leads on the high voltage rail and watch until the next pop. If your voltage drops when she pops we may have a winner.

I'd swap tubes with known good ones.

[Structo]

Heheheh, make sure you don't have a cell phone in your pocket when troubleshooting.

Make sure the noise is not in the circuit that the amp is plugged into.

I was working on one and couldn't figure out a nasty buzzing noise until I glanced above me at a fluorescent light fixture......

[azcreamery]

Thanks for the suggestions.

I tested each filter cap noting zero change in voltage. Same for the resistors and coupling caps. I don't have a flourescent light in the room- Also, I brought the amp to my brothers house and pluged into his speaker cabinet using his cables, and the popping continued.

Could the problem be with the OT? If so, how could I test this?

[CaseyJones]

Jeez, it sounds like a wonky horizontal output in an old TV. Every so often the high voltage would arc and yer picture would momentarily get funky...

It sounds like something is discharging on a regular schedule. It's too slow to be low frequency oscillation. 1/10hz?

Probably not an OT IMHO.

[Structo]

Well the tubes should be the first suspects in any build or amp.

Even if the tubes are brand new.
The failure rate is phenomenal.

If you have known good preamp tubes, substitute it one by one in the preamp and PI.

Then the power tubes.

[dave g]

I wouldn't trust a DMM to find something like this. Use a scope to look at each individual node in the signal path.

[Andy Le Blanc]

ground the input to the phase inverter...... if it keeps pop-in itll be in the
power side of the amp.... check the power tube sockets and the tube bases
for little burns...... check your grounds........ check for debris around the
socket pins....... Ive seen this in some old amps caused by dust or dead bugs.....
also from conductive phenolic sockets and boards.....

[Jana]

I know you said you have changed tubes but it sure sounds like a bad tube.

The thing is, if this popping noise is being introduced on the the B+ rail, then turning volumes up and down might be misleading. For example, turning the volumes all the way down might lead one to believe that it is in the power section when in fact it might be coming from an earlier stage... the B+ rail is having a spike introduced on it.

What would I do?

I would pull all the tubes except the power tubes, turn it on, see what happens. Pop gone? okay, insert phase tube, see what happens. continue on down the line until pop returns. that might help to localize it. Maybe it was the tube? maybe not. If not, check all the connections, check for a leaking coupling cap.

Maybe the previous didn't work at all and the popping was there even with all the tubes pulled. Okay, plan B. The same logic but this time disconnecting nodes in the B+ rail. Lift an end of the resistor feeding the phase inverter (and everything else downstream). Now the only thing getting power is the plates and screens of the power tubes. Pop gone? okay, reconnect that resistor, disconnect the next one, proceed on down the line.

Let's say you isolate it to the phase inverter section. Remove the tube, disconnect the plate resistors, pop still there? Well, it is sure pointing to that filter cap isn't it, disconnect that cap, test again.

Sometimes with these head scratchers it's a matter of systematically isolating parts.

[azcreamery]

I tried everything, without success. Finally, I brought the amp to a tech with 40 years experience. After looking at the amp he decided it was likely the OT. I notified the Heyboer distributor (Chis at 'toneslut') and he shipped a fresh OT directly to the amp tech that same day. Replacing the OT solved the problem.

[Structo]

Wow, never would have suspected that.

Sounds like a smart and good tech.

[Andy Le Blanc]

after 40 years I bet he's had more than a few that have been stumpers

how was it the output tranny?

[Richie]

I've seen power transformers cause this problem..