1964 Vox AC30/6 TB

One of the all time classics, the extremely collectible Vox AC30 comes in many different versions and models. This is the 6 input JMI manufactured version with the Top Boost circuit built in from the factory. I also think this happens to be the most user friendly and better sounding Vox amp from this era.

This guy came in with popping, crackling and weird noises happening and the sound would randomly cut out. However the amp did not need a ton of work - it had already had an excellent electronic restoration done in the past by Lowell Hunt of Hunt Amplification in Phoenix, AZ. I found 7 different original carbon comp resistors (6 plate load, 1 cathode load) had drifted very high which was responsible for a good lot of the problems. The 56k cathode resistor in the Top Boost cathode follower had drifted all the way to 440k!!

All plate load/cathode resistors were replaced with vintage spec new production 1/2 watt carbon comp type to retain originality and collector’s value. A good deal of sloppy wiring work was cleaned up inside that had been many years earlier. The speaker wiring had to be re-done because the original wires were badly spliced together and not very reliable. The 2 coupling caps following the phase inverter were leaking and out of spec - they were replaced with .1uf 600v CDE Orange Drops.

The original tubes did not all test good and were partially replaced. Final tube lineup: V1 = Sovtek 12AX7LPS, V2 = JJ 12AX7S GOLD, V3-V6 = EHX EL84 Matched Quad, V7 = JJ 12AX7S GOLD, V8 = JJ 12AU7 V9 = JJ 12AX7S, V10 = Sovtek 5AR4. The cathode bias on the EL84 power tubes was sitting at an unsafe %154 plate dissipation - The original 47 ohm cathode resistor was cooled down to an 82 ohm 10 watt type resulting in a correct %103 plate dissipation and a B+ of 340vdc. This old Vox is back to perfect health now.