Ampeg V4B Bass Amp Refurbishment

This wonderful old Selmer-era Ampeg bass head was pulled out of its retirement in the closet and put back into service.  But it had a few issues to address, so that it could reliably pump out the tones that is the Ampeg Experience.


01V4B the patientThis unit appears to be absolutely factory stock.  The Houston humidity has had an effect on the aluminum faceplate.

02V4V rear pnl1Taking a tour of the rear panel, we see a bracket upon which the line cord may be wrapped.

03V4B rear pnl2The convenience outlet is a three-prong unit, which is nice.  The hum balance control adjusts the bias current in the output tubes to be the same.

04V4B rear pnl3Magnavox owned both Selmer and Ampeg for a while, if I recall correctly.  Note the tube layout information.

05V4B rear pnl4Here is the other bracket for the cord, and the output jacks and impedance switching.

06V4B cordDude, are you still smoking?

07V4B internals1This is a nice intersection between hand wiring and the use of an etched circuit board.

08V4B internals2This cap and the bleeder resistors are slated for replacement.

09V4B cap1Yes, you can still get multi-section capacitors if you shop diligently.

10V4B cap2The prongs of the new capacitor need to fit in the slots in the chassis.

11V4B cap3There is plenty of height inside the chassis, but it doesn’t hurt to document what we have.

12V4B cap4Likewise, we’re documenting what we have.

13V4B cap1Here is the new multi-sectioned filter capacitor and the hole where it goes in the background.

14V4B cap2The outer can of all of the capacitors is isolated from the chassis, so these green fiberglass spacers are used under the capacitor.

15V4B cap3I think we’re done here!

16V4B cap4The new cap looks nice on the top of the chassis.

17V4B cap3The axial filter capacitor will be replaced with this part.  I am forming the leads to appear in a manner similar to the original part, seen above.  A little Teflon insulating tubing helps keep the electricity under control.

18V4B cap4Wires will be attached to the terminals, so the leads are formed into a loop to accept the wires.

19V4B cap5The wire bending is done with a hand-tool called “chain nose pliers.”

20V4B cap6The original part has a mounting ring around it.  We will need to recycle this mounting scheme to maintain originality.

21V4B cap7The ring is off!  I was a little concerned that I would mess it up, but a little heat was all it took.

22V4B cap8Here is the original mounting ring applied to the new capacitor.

23V4B cap9The ring can slide around just a little bit to give us a nice-looking mounting solution.

24V4B cap10And here we are, all wired up and ready to go back to work.

25V4B good capsThese guys have been replaced recently, and they check out as new.  So, they will remain in service.

26V4B controlsSome of the front panel slide switches were dirty, so some cleaner and lubricant were sprayed into them.

27V4B top1Now that the caps are changed out, let’s look at the top of the chassis.  The output transformer and output tubes are on the left side of the chassis.

28V4B top2The preamp tubes and power transformer are at the right end of the chassis.

29V4B top2detail1The open areas around the tube sockets are a nice touch.  The chassis is steel and very stiff, even with the relief.

30V4B top2detail2More low and medium voltage goodness at the other end of the slot.  Nearly every schematic test point is accessible from the top of the unit without turning it over on the bench.

31V4B Magnavox 12DW7This 6K11 Compactron tube tests very good, with each of the sections closely matched to the others.  Good News!

32V4B inputjax1The input jacks were corroded, so these were changed out with new Amphenol units.

33V4B inputjax2Here is the inside-the-chassis view of the new jacks.

34V4B indicator1The neon indicator for the AC power was functional, but the indicator for the high voltage was not.

35V4B indicator2So, this neon indicator will take its place.  The mounting hole is the same size, but the new part is chrome.  What to do?

36V4B indicator3We scrubbed the chrome ring with steel wool, then applied several coats of black polyurethane paint to the bezel.

37V4B Indicator4Here are both indicators.  The high voltage is amber, and the AC indicator is red, as it was when the amp came from the factory.  The colors are a bit messed-up because of the jpeg processing in the camera…  looks good in Real Life!

38V4B Happy CustomerAnother happy customer picks up his finished bass head!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE