rustling noise from Champ-a-like

[paggerman]

Hi all. I hope you are all well. I've been away from the soldering iron for a little while and have been concentrating on learning to play. The amp I use most is a little Champ-a-like that I have built. The PT and OPT and speaker are from an old radiogram. I have used diodes to rectify. The valves are a 6N2P and a 6V6. It's got a beautiful sound.

BUT, it generates a rustling sound, somewhat like the runoff groove of a vinyl record. The sound is variable. Sometimes it has a 'burst' and fades. Sometimes it stops for a short while. It doesn't change volume if I turn the volume knob. I have resoldered just about every joint in the thing, but still it doesn't go away. I have squirted contact cleaner into the pot and valve sockets. I have changed the 6v6. Nothing seems to make any difference.

I don't expect a definitive answer, but if anyone has any suggestions for potential problem points or resolutions I'd like to hear them.

Very many thanks in advance

[kleuck]

Not sure, but i encountered this issue once, and i was a tube issue, in my case an ECL82 (power and pre in the same bottle) so try to swap the preamp tube too.

[sleepingAwake]

Hello
I'm kinda of a newb but I'll throw a couple things out there and see if they stick.

Cold solder joint?
Did you happen to use an old circuit board for the build and it's conducting?
Some sort of inductance in the circuit?

[52 Bill]

Tubes are always a good place to start, then there are plate resistors that can get noisy.

Could be any number of things, try and see if you can isolate the problem to a specific part of the circuit. Is the noise changed by any of the controls? If you pull the preamp tube does it stop?

[Chuck H]

+++ to all. Bad solder joint, flux in a tube socket pin connector or a bad tube.

[booj]

I've had a couple of amps with thunderstorm noise - I guess similar to vinyl groove run - that turned out to be a bad coupling cap.

[paggerman]

And the winner is...

All of you. I think everyone suggested the pre-amp valve and I swapped it out with a known good one and it worked brilliantly. it was probably the only thing I hadn't tried because it was a brand new valve and just about everything else was pre-used. I suppose when I pay a two bucks a piece for the 6N2P I can't complain if there is the occasional dud.

Thanks everyone.

[kleuck]

You should use 6N2P-EV only, they are not the same quality at all.

[paggerman]

You should use 6N2P-EV only, they are not the same quality at all.

The replacement is an -EV and you're absolutely right. The sound is completely different. I kinda liked the 'gurgling' sound of the dud, but this one is much punchier and clearer. I can hear the individual strings as I strum.

Good advice. Well worth the 'upgrade'.

[kleuck]

A well known French tech compares them (the "EV") to the Mazda silver plate, which are the best tube of all time imo, construction wise, and sound wise if you are after absolute minimum noise and maximum clarity, though i don't like them for the guitar and oin the contrary he finds the "non-EV" crappy.