1972 Ampeg V-4B

The V-4 is one of Ampeg’s most popular bass and guitar amplifiers ever made (right behind the SVT and B-15) and has been used by Juan Alderete, Peter Hook, and Josh Homme. Its is also a fine example of the brilliant electrical engineering happening at Ampeg during it’s heyday - The amp includes a Baxandall tone stack, a fully independent active “Ring-of Three” Mid-EQ, use of Compactron tubes, and a very linear almost Hi-Fi like design that puts out 100+ Watts RMS. The VT-22 is basically the same amp with Reverb and in Combo form. These amps can have problems with overheating resistors and under-rated parts in general but are of very good quality if restored correctly and with an emphasis on preventative maintenance. This one was brought to me after being taken in for repair a number of times and still was not right. When I got it, it had blown screen resistors, over-heated plate resistors, and a shorted preamp tube.

The amp was completely restored. The amp had been partially restored by another tech, but many things were left undone or done with sloppy craftsmanship - many parts were installed on the wrong side of the PCB because it took less time. All of the electrolytic CE brand cap cans were left in place as they were installed correctly, but the power dropping resistors attached were replaced with new 2 Watt Metal Film type units. The bias caps were replaced with CE brand electrolytics with upgraded voltage and temperature ratings. The entire bias circuit was rebuilt with upgraded 1000v film caps, and 2 Watt Metal Oxide/Metal Film resistors. New 5 Watt Wire-Wound power dropping resistors were installed for better reliability and lower noise floor. The same was done for a number plate resistors which were either under-rated or showed signs of heat damage - These were replaced with 2 Watt Metal Oxide/Metal Film type units. Upgraded 5 Watt/7 Watt Cement resistors were installed for the screens of the power tubes and associated circuit.

Upgraded GP10Y-E3/54 1.6KV 1A Diodes were installed for the fly-back protection circuits. The death cap was removed rendering the polarity part of the power switch deactivated for safety. A new 120v Neon Pilot Light in matching NOS style was installed as the one currently in place was a homemade hacked together part that while working was not very stable and looked terrible. All of these parts were installed on the correct side of the PCB with clean technique to restore collectors value and top quality craftsmanship to the amp. All of the preventative maintenance that should have been done originally was taken care of.

Amp was completely re-tubed with the following lineup: V1/V2 = EHX 12AX7, V3 = NOS GE 12DW7, V4 = EHX 12AU7, V5 = NOS Tungsol 6K11, V6-V9 = JJ 6L6GC Matched Quad. These tubes were picked for best tone, and reliability. The 6L6GC's Fixed Bias was set to %52 Class AB Plate Dissipation with a B+ of 525VDC. The Hum-Balance Heater Adjust Pot was replaced with 2 Watt Metal Film Resistors which are more reliable - a Chassis-Hole Cover was installed for cosmetic purposes.

Lastly all of the rubber shock-mounts attached to the metal stand-off panels that carry the amps' weight were replaced with custom made replicas from Fliptops.net in NYC as the OEM parts are no longer made. The originals in place were broken, ripped, and could no longer keep the amp upright. Amp was cleaned, hardware tightened, and now functions normally.