Ampeg V4 issues

[Geezer Brown]

Hey all,

I recently became the proud owner of a Magnavox Era White-Rocker Non-Master V4B, but am now noticing some issues.

When I turn on the Amp, there is an intermittent buzzing that sounds like a tesla coil/ static electricity that lasts for 5-10 minutes before going away. I suspect a bad filter cap. I called my local tech and he agreed. What I'm wondering is does he only need to replace the bad cap or re cap the whole thing? I've heard (and I could be totally wrong here in assuming, I respect techs and their craft) that sometimes techs will charge you for a full recap job even if you don't need it, and it can make the tone worse. His rates are pretty steep from what I gather, but obviously will be worth it. Also, should I just buy the caps on flipped and give them to him?


Also, the ultra low switch turns the tone into a cross between mud and ass, and there is a considerable drop in volume. Channel 1 is significantly quieter than channel 2.

Thanks in advance.

 

[JimmyM]

Techs generally hate it if you bring in your own parts. Not only that, he may not have to replace them all to fix the amp, and you may end up buying a bunch of caps for nothing, although an amp that old may actually need all new caps all around. My advice is if you like his work, let him do his job.

 

[coreyfyfe]

If the amp is old enough to need a cap job you should do all of he caps. They're ticking bombs waiting to fail at that point, it will save you headache to have them all done at once. The filter caps are in your power supply and shouldn't cause issues with tone to replace them.

Your tech can likely get the caps cheaper than you could buy them retail so you'd likely pay more to supply the parts.

A lot of people call the ultra low switch the mud button so not surprised you don't like the tone. That's not to say it's not a circuit issue, but you might just not like what it does to the sound. As for volume differences between the channels, could be a bad tube on channel 2, could be related to failing components, etc. I'm sure your tech will sort it out.

 

[beans-on-toast]

As was mentioned, all the electrolytic caps in the amp should be changed, especially if they are original.

Coupling caps can get leaky and cause static. The tube sockets and slide switches need to be checked and cleaned with Deoxit. Same for the jacks. Clean the pots with Deoxit D5 spray. The amp should have a general checkup.

Check the condition of the insulating washers of the speaker output jacks both on the inside and outside of the chassis. If they aren't there, there will be a ground loop hum.

I wouldn't hurt to look at all the bias circuit components. Change the electrolytic caps (or cap depending on the revision) in that circuit. C16 takes a lot of stress and can fail in these amps (I use an X2 safety cap here) and R50 (56K 5%) can go out of spec.

On V4, R30 and R31 (47K) can be bumped up to 2W 5% or better.

Check the power tube plate and screen resistors.

 

[GreyBeard]

Sounds like a bad idea to me. Will probably piss the guy off.

 

[RoadRanger]

Also, the ultra low switch turns the tone into a cross between mud and ass, and there is a considerable drop in volume.

Yah, that's the switch you use when you don't know the notes to the song - just switch it on and thump away, nobody will be able to hear what notes you are playing if you keep to the bottom two strings below the fifth fret .

 

[Bill Hughes]

That ultra low switch notches in the upper frequencies to give the illusion of more bass without causing overload on the low end. It was formulated for certain Gibson basses. The same principle was used in other Ampeg and some Fender amps, as well as the Peavey Probass 1000 preamp.

As far as the crackles and noises go, that amp in possibly 45 years old. before you re-cap you should clean up the circuit boards with electrical solvent.
Bill