deveng
Well-known member
Gents,
Here's my finished mic based on the AC701 schematic for the Telefunken 251. Its got an under-heated Heinz Kaufman 5840 connected as a triode, CEK-12 capsule, T14/a transformer and a Telefunken 251F power supply with a adjusted B+ and filament voltages for the 5840. Of course the plate and cathode resistors were changed. Polystyrene caps for the plate and capsule shunts, low impedance electrolytic for Ck and polypropylene for the series output capacitor. Its wired for cardioid only.
The body is closer to a C12 diameter but I use the double mesh on the head basket like the 251 (excluding the top mesh). Worked on first power up and is very quiet. Only had 2 5840's so I think I got lucky with this one being low noise. I've only recorded 3 vocal tracks as yet so the verdict is out on how it sounds overall. The vocal tracks were warm, fat and not sibilant with a smooth high end. But, I'll reserve my full opinion until after its tested with multiple instrument sources with more high frequency content than voice.
All high impedance parts are mounted just under the capsule on a disc through hole board which could be changed out fairly easily with a different disc with correct components for a 6072 tube. Mic body length is setup to allow room for the 6072 if I ever go that route.
More pics to follow
Regards,
Jeff
Here's my finished mic based on the AC701 schematic for the Telefunken 251. Its got an under-heated Heinz Kaufman 5840 connected as a triode, CEK-12 capsule, T14/a transformer and a Telefunken 251F power supply with a adjusted B+ and filament voltages for the 5840. Of course the plate and cathode resistors were changed. Polystyrene caps for the plate and capsule shunts, low impedance electrolytic for Ck and polypropylene for the series output capacitor. Its wired for cardioid only.
The body is closer to a C12 diameter but I use the double mesh on the head basket like the 251 (excluding the top mesh). Worked on first power up and is very quiet. Only had 2 5840's so I think I got lucky with this one being low noise. I've only recorded 3 vocal tracks as yet so the verdict is out on how it sounds overall. The vocal tracks were warm, fat and not sibilant with a smooth high end. But, I'll reserve my full opinion until after its tested with multiple instrument sources with more high frequency content than voice.
All high impedance parts are mounted just under the capsule on a disc through hole board which could be changed out fairly easily with a different disc with correct components for a 6072 tube. Mic body length is setup to allow room for the 6072 if I ever go that route.
More pics to follow
Regards,
Jeff