I recently bought a pair of Hammond M100 nuvistor condenser mics.
They can be seen here.
The PSU is strange. It is a valve / transistor hybrid. The HT section uses a 0C2 valve voltage regulator! The heater section is solid-state.
Anyway, the audio output of the PSU is unbalanced, but there seems to be quite a bit of noise despite moving the cable around (I will be balancing the output with transformers). I scoped the voltages going to the mic which are -5V for the heater and also ~115V and 90V (not sure why two HT voltages). Anyway, I was more interested in the PSU noise. There is 100mV of 100Hz noise on each of the power supply pins. Is this too much? The caps are likely quite dry which is why I thought I better check for ripple.
Cheers,
Roddy
They can be seen here.
The PSU is strange. It is a valve / transistor hybrid. The HT section uses a 0C2 valve voltage regulator! The heater section is solid-state.
Anyway, the audio output of the PSU is unbalanced, but there seems to be quite a bit of noise despite moving the cable around (I will be balancing the output with transformers). I scoped the voltages going to the mic which are -5V for the heater and also ~115V and 90V (not sure why two HT voltages). Anyway, I was more interested in the PSU noise. There is 100mV of 100Hz noise on each of the power supply pins. Is this too much? The caps are likely quite dry which is why I thought I better check for ripple.
Cheers,
Roddy