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ampeg v4 volume popping in and out....

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9/22/1999 3:39 AM

ampeg v4 volume popping in and out....

hi.

I have an early magnavox era v4 running sovtek 6L6WGC's with no mods. after playing through it for about 15 minutes, the volume will cut out, then back in, very sporadically, sometimes rapidly. a bit of popping and crackling accompanies this. the power tubes flash a nice blue in perfect unison, all 4 at the same time while this popping is occuring. i tried a different set of power tubes but the problem persists. I even traded the bulk of the preamp tubes but it still does it. any ideas?

-chris

9/22/1999 5:59 AM

I worked on a v4 recently that cutting out and such.

It could be a loose connection anywhere, but be glad to suggest some trouble shooting ideas. I was able to fix this V-4 by simply cleaning the preamp tube sockets with spray contact cleaner pushing the tubes in and out of the socket and then wire brushing the tube pins. Use the no residue

quick dry cleaner and soft brass wire brush. Also use the cleaner on the pots and rotate them while spraying in the small opening. There are two speaker jacks on the back panel. one of them must have a rubber washer.

also spray clean the input jack contact switch and check to see that the nuts are snug. The hum balance pot can cause problems too. sometimes poking around with a wooden stick when powered up can help reveal the intermittin problem, but you better know somethin about what your doin, if you go this far. I think that amp goes up to about 500 volts that can kill you!

9/22/1999 1:52 PM

What are the plate & screen voltages in your amp? They're usually very high, above 500vdc.

Although the 7027s the amp came with can be considered as "super-duty 6L6GCs", and the amp's designers intended that high quality US made 6L6GCs and 7581As could be substituted without alteration, some modern day 6L6 types don't fill all the requirements to be simply plugged in to a late model V-4.

I suspect that the tubes are arcing internally when a strong signal tries to get through. I would suggest you use some NOS tubes, such as 6L6WGC (which have become plentiful recently, due to auction of government stockpiles), or even the 6BG6 tubes w/adapter kits offered by SND, if you want simple plug & play replacements. Maybe someone else will add which particular tubes they've had success with in unmodified V-4s.

The amp can be modified to safely run modern production 6L6 type tubes by lowering the screen supply voltage, and increasing the series grid resistor size. Maximum power output will be lower than original, but that shouldn't be a problem for guitar. If you're using this amp for bass, you can convert it to use 6550 tubes by removing the tube retainer jaw clamps and modifying the bias supply.

Good reading on this Ampeg- Output tube subject can be found on the Triode Electronics website. Highly recommended.

9/23/1999 5:01 AM

Psycho Bass Guy

While the Sovtek's ain't the best choice available, they shouldn't do that. Check out all the posts relating to the SVT which is just a big version of the V4. Ampegs have a wonderful tendency to run fine and then go all to hell when one bad part causes a cascade failure. Something in your output is obviously intermittent which could be anything from the power suppy to the tubes themselves. Go through the amp with a fine toothed comb get it working and go through it again. They're like cars; without regular maintence you can develop big problems.

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