need help w/ ampeg V4

[methodofcontrol]

my early 70's V4 makes popping noises. it seems to only happen when the volume is up. but once it starts it will continue intermittently even w/ the volume all the way down! none of the tone controls effects the popping. and i've had this problem for almost 2 years. i've opened up the amp on several occasions to change out componants here and there and try to diagnose the issue.
i've resoldered EVERYTHING on the two main boards hoping to fix a cold joint. and i've tried several known good tubes in all locations.
here's the weird thing:
when i use an attenuator for bedroom levels, i can dime the amp hard for 2 hours and not hear a peep. also, i have an ampeg mastervolume pedal for the back of the amp, and when i use that at bedroom levels i can dime the preamp and not hear a peep either.
does this mean i have a problem in the power section? is it arcing? where should i look? ack!

[Mouthurst]

Ampeg pwr xfrmr too?

Hi, this is my first post here and having experienced a similar problem in a V2 thought I'd share a story which may be of interest.

Of course popping noises can be a bunch of things and intermitent things hard to diagnose, but maybe...
I diagnosed my pwr xfrmr to be no good...well it was because it was made poorly, this I found out when I removed it for inspection.

Mine was acting strange sometimes really whacky and sometimes okay.Perhaps it was arcing in the HV and shorting out or whatever.. Well I got it to act okay eventually by gently banging it around.Then with great hope that it would stay that way, First thing I did is re-dip it in varnish and bake it, retested and banged it around some more, I dont know what was wrong in there-moisture, oxidzation particles... or thin varnish? Is that why I like these things ...the mystique?
Works like new now. Just thought this story might help.
That part was pretty shoddily made IMO. I got lucky, hope you do.
Wm. Mouthurst

[Enzo]

If the pops persist with all controls to zero, it is more likely in the power amp or power supply. Got a scope? Look for the noise signal on the B+ and in teh stages. Look for it on the bias supply.

There is a 12AU7 phase splitter V4 driving the power tubes. Pull it. Did the pop stop? If not, the pop is in the power tube stage or the OT. If so, then the pop is in an earlier stage.

Restore the 12AU7 and pull the 12DW7 at V3. Once again if the pop stops, then tV3 or before is the problem, if it remains the pop is after that tube.

If grounding the external amp jacks kills the pop, it is coming in before the jacks.

[methodofcontrol]

enzo- thanks for the tips. as always, a wealth of info!

mouthurst- i really hope i don't have the same problem you did. that sounds terrible! but thanks for the input, i'll definately look into it.

[Mars Amp Repair]

Ampeg v-2 woes

hello,
once you've isolated the stage (or even if you can't) one other handy test tool you can use for intermittent components like resistors or non-electrolytic caps is alternate freeze spraying & heating (with solder iron)....I've isolated very stubborn noisey carbon resistors this way as well as those disturbing disc caps.
Caution; it doesn't work so good on tubes, tho

Of course freeze spray is much more effective on semi-conductors.

Also I've found some really weird issues with dirt/metal filings in controls that won't clean up with Deoxit, that makes them act very strange......that's pretty rare tho.

glen

[methodofcontrol]

yeah i've tried the freezing thing. i thought i found a bad cap and i replaced it, but i still have some noises. the biggest problem w/ the amp is whenever i have the ambition and the time to troubleshoot it, it works perfectly. and whenever i think, "oh, that amp worked well last time i plugged it in....i won't need to set up my workbench for troubleshooting if i just want to play it for a few minutes" then it goes all crappy.
i've decided, if it comes down to it in the near future...i will be rebuilding the entire pre amp. but w/ that plan in mind, it will be a bit before i open it up again. i just got through w/ my last fix-it-project. i'll take a breather for a few days before i open up the V4 again.