Ampeg V4B amp issues - opinions/advice?

[JMV]

I have a Linden, NJ version Ampeg V4B head that is not working properly. The output ranges from nothing to very weak to almost normal volume, depending on whether the Ultra Low rocker switch is positioned "just so". Very touchy, seems like this rocker (possibly the Ultra Hi and 3-position freq ones too) is dirty. Lots of static as the switch is "rocked" from off to on.

Any suggestions or opinions would be welcomed! Not sure if these switches could be culprit of low output and if so, what is best practice for cleaning or replacing?

Thanks in advance everyone...

 

[Wasnex]

I have a Linden, NJ version Ampeg V4B head that is not working properly. The output ranges from nothing to very weak to almost normal volume, depending on whether the Ultra Low rocker switch is positioned "just so". Very touchy, seems like this rocker (possibly the Ultra Hi and 3-position freq ones too) is dirty. Lots of static as the switch is "rocked" from off to on.

Any suggestions or opinions would be welcomed! Not sure if these switches could be culprit of low output and if so, what is best practice for cleaning or replacing?

Thanks in advance everyone...

The switch could definitely be the problem. It could be dirty, oxidized, broken, or have a loose solder joint. There may be a bad capacitor in the circuit that is letting voltage through to the switch, which would cause a loud pop ever time you change it from one setting to the other. This is arcing and over time it will either form a carbon deposit or break down the plating.

If you don't know the solution, the best bet is to take the amp to a technician who does.

 

[jbrew73]

Did you test both channels?

 

[Wasnex]

Did you test both channels?

AFAIK, the V4B only has one channel.

 

[beans-on-toast]

The switch can be cleaned with deoxit. A lot of gunk can come out. This has to be done carefully, you just want apply the cleaner on the switch contacts.

There are many possible bad solder joints and wires in the vintage V4B that need to be examined. In general, the wire connections can be delicate.

 

[coreyfyfe]

AFAIK, the V4B only has one channel.

The original V4B has two input channels with a shared EQ same as the V4

 

[Wasnex]

The original V4B has two input channels with a shared EQ same as the V4

Oh I see. There are two front ends, but only one shared tone stack.

 

[JMV]

Many thanks to all for the great advise and suggestions. I'll try cleaning switch contacts as suggested, and once I have them out and accessible will also take a look at solder connections throughout for any obvious loose ones. Sounds like extreme care should be taken - aside from charged caps, etc.... also given the delicate condition the aged amp might be in

Also to confirm a couple things... yes, it's two channel with an independent vol control for each of two front panel inputs and both fed into common eq section. FWIW, the second one has a gentler taper so its volume doesn't increase as quickly. Don't know if this is original design??... this amp was a "hot mess" when acquired used back in the 70's. It was slated to be scrapped, but the dealer's tech told me it's mine if I covered the repairs that turned out to be $125 back then. (It wasn't pretty, but it got me up and running after loosing only two heads I owned at time as result of breakin/theft).

Also, as Wasnex pointed out there could be possible cap issues... but there is no loud popping, so fingers crossed maybe simple cleaning?!?! I'll report back once I get chance to take apart, meanwhile thanks again to all!

 

[JMV]

... and oh yes, I checked both channels and they behave identically

 

[Jeff Scott]

Oh I see. There are two front ends, but only one shared tone stack.

But, this is key to the OP's issues (the amp, not the OP ). The amp could have 12 channels, but if they all go through that same, single EQ section, what's the difference?

 

[Wasnex]

But, this is key to the OP's issues (the amp, not the OP ). The amp could have 12 channels, but if they all go through that same, single EQ section, what's the difference?

The bass, mid, and treble controls are shared. However, if I read the schematic correctly, each channel has it's own Ultra Low and Ultra High circuit, with linked switching. So from an functional stand point, there is one Ultra Low control and one Ultra High control, but from a trouble shooting standpoint there are two completely independent circuits.

 

[Jeff Scott]

Ah, maybe that's why I liked the old V4-B amps. Are the current ones similar (one thing I know I don't like on the modern RI model is the cyclops indicator light - I liked the old two indicator original)?