Tube Mic PSU Upgrade Service

You'll find the common Chinese-made power supply within most of the sub-$2000 tube mics on the market, e.g.: Avantone CV-12 BadAax T11A Apex 460 older Telefunken RFT series mics (AK-47, AR-51, CU-29, M16) We have seen numerous problems with this design: The B+ rail is unregulated, which means the sound of the mic could change as wall voltage naturally drifts. (It is not uncommon for utility AC to vary by 10% over the course of a day.) The B+ rail voltage is often too high. Many of these mics use capsules designed for 60V polarization voltage. The mic circuit uses one-half of the B+ rail to polarize the capsule. But the B+ rail often runs at 140V or higher, leading to the capsule seeing 70V (or more). This limits the mic's SPL ceiling and headroom. The F+ or heater voltage is often too high. The 6072 and related 12A_7 family of tubes should see 6.3V max on the heater (assuming the two heater elements are wired in parallel, which is typically the case). Most mic designers lower heater