kurganyuriy1987
Member
- Joined
- Oct 10, 2012
- Messages
- 11
Tubetec said:Thats quite similar to an EF86 based mic I built, back plate connected to polarising voltage ,capsule front direct to grid like the U47. 1gigaohm grid resistor does seem a bit high ,my guess is you'd need to very carefully select your ef86 to work with that value .U67 uses a similar value but ef86's dont live all that long in them in my experience . 40 megohms is the listed as the highest grid resistor for the ef86 I believe ,I ended up using an 80 or 120 meg resistor in mine .Worth using a ptfe tube socket in this application also if you can get it .
AusTex64 said:I learned from Oliver Archut to use a trimpot to dial in cathode bias exactly. He did this on CS1 and CS4.
ln76d said:Here you have two options of EF86 mic which fit k47 capsule
https://groupdiy.com/index.php?topic=64687.msg819492#msg819492
https://groupdiy.com/index.php?topic=62441.0
S316 use psu switch to change polarisation voltage, you can skip it - for k47 c3 isn't needed.
High impedance resistors from 100M to 470M.
For your schematic - don't need to install two plate resistors and filtering cap - there's marginal benefit from it, but the phase is much better without it.
For cathode - G7 arrangement was experimental to use feedback. Without any feedback this arrangement doesn't work good.
Choose between one cap and one resistor or just one resistor.
Output capacitor 0.5uF is enough and there's positive audible benefit from using lower value. 2.2uF is totally to high. In both cases low end level is the same. Proper cathode biasing will give proper low end level
Polarisation voltage - you need to use divider! Currently your capsule will die quickly with 160V. Max what you can use is 3M/2M (this side to ground) and add high impedance resistor + filtering cap.
Hope this help somehow
Khron said:Your multimeter has an input impedance of 1M, or maaaaaybe 10M if you're lucky. Together with that 100M, that forms a (huge) voltage divider That's why you're measuring next-to-nothing "after" it.
PS: For whatever reason, i can't see the attachment. But if you did that 3.3meg / 1meg divider from 160v, unless my math is seriously wrong, that would only result in about 37. ???
160v x 1meg / 4.3meg (total) = 160v * 0.23 = 37.2
KrIVIUM2323 said:Like in the 'Church' mic Piotr?
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