We had the chance to get one of these in the shop recently and discovered interestingly enough that's PSU design and components list were very similar to mics we already modify, so we came up with a quick and easy upgrade to this popular affordable tube mic.
In two of the mics we've looked at, we observed that MXL were trying a common trick used to beef up the performance of more economical tube mic cables, doubling up on the leads used to carry B+ voltage in place of having a heavier gauge set of leads to carry the B+ and circuit ground signals as seen with higher end tube mic cable. However, oddly enough, they forgot to carry this thought through and put the necessary jumpers on the microphone side... only on the PSU side. So we correct this with the necessary jumper, and also test/clean/spray the stock cable. This will give a bit of an easier time to the PSU. We also add a dedicated chassis ground wire to the microphone, and use an emory cloth to take away the paint at the base of either end of the mic body tube. This allows ground contact to pass all the way through from the properly grounded microphone frame, eliminating a lot of the handling noises and buzz/hum/ground noises that these mics sometimes exhibit.
In addition to this, we add a wound ferrite ring on both the incoming B+ and H+ leads to help prevent any RF interference from coming into the tube circuitry, which was a known issue on some of the earlier (pre Mogami) versions of the MXL tube mic line.
The tube is upgraded to a TAD (Germany) 6072 Highgrade valve with Sandy Levy tube damper ring also installed, and the tube socket pins are sprayed with DeOxit and re-tensioned if necessary.
All electrolytic capcitors are replaced in both the PSU and the microphone with the best available Nichicon long life and audio grade parts.
The capsule will be cleaned and re-terminated.
The MXL V69 is a bit of a diamond in the rough. It has a decent, warm, full sound, albeit not as larger than life as a good transformer circuit can be. But with these mods the mic will have a higher build quality and should last reliably for a lifetime, and operate cleanly and perform at its very best.
MXL V69M tube microphone upgrade
just to be clear, this is a mod where you send in the mic, 7 pin cable, and power supply.