S76 - Tube Microphone (6AU6, K67, deemphasis, 9.5:1-10:1)

ln76d · Jul 31, 2017

I have 6j4p, ive tested alsofew other 6au6e//f94 in my builds.
Yeap it's pretty good tube, but my favourite is Thomson military 6au6, in every build worked better than 6j4p, tele ef94 and others.

tardishead · Aug 15, 2017

Are you going to post the new design soon? Very excited to see it

ln76d · Aug 16, 2017

tardishead said:
Are you going to post the new design soon? Very excited to see it

I will think about that

Have no time currently to draw schematic.
Definately i will post it in black market for sale

Anyway there's truly similar to S76, main difference is tube connection in parallel and transformer ratio.
Deemphasis network is practically the same.

RuudNL · Aug 17, 2017

I think it might be a good idea to reduce the value of the 100 M.ohm resistor.
The R-C time (100 M.ohm/0.5uF) is now in the order of 50 seconds!
Of course the tube has to heat up also, but still this time constant is much longer than needed.
10 M.ohm would probably be better, or maybe even lower.

Khron · Aug 17, 2017

That's the exact observation i made over in the FET847 thread - the last stage in the capsule bias voltage was a 1G / 100n RC low-pass, which gives a 100sec RC constant (and that's when the voltage "only" reaches 63% of the maximum), so about 500sec until it reaches its max

RuudNL said:
I think it might be a good idea to reduce the value of the 100 M.ohm resistor.
The R-C time (100 M.ohm/0.5uF) is now in the order of 50 seconds!
Of course the tube has to heat up also, but still this time constant is much longer than needed.
10 M.ohm would probably be better, or maybe even lower.