Electro Harmonix 12AY7 Mic Preamp - output capacitor selection?

I would like to upgrade capacitors C5 and C8 in the EH 12ay7 preamp but wounder what brand and type to select?

I guess it should be specified for a minimum of 200volt, or preferable 250volt ?, any suggestions for a high voltage 47uF cap in this type of audio application?

Are you sure the values of R12 and R13 are correct?

Cheers

Ian

ruffrecords said:

Are you sure the values of R12 and R13 are correct?

Cheers

Ian

Click to expand...

They are not correct in the schematic above, "un-modded" they are 33k in that circuit. Mine is unmodded.

http://www.labjc.com/?p=966

Offhand, I'd say between a 330K pull-down and a 220K internal load (plus whatever is on the end of the cable), it hardly matters what cap you use. Resistance dominates.

This is far enough away from most designs that I don't think anybody has experience.

Put in whatever caps you think will be better.

using 12AY or 12AU?

Nichicon makes good stuff,

non lytic would be good too, but need a big case to fit them,

tonedude said:

They are not correct in the schematic above, "un-modded" they are 33k in that circuit. Mine is unmodded.

http://www.labjc.com/?p=966

Click to expand...

33K is a much more sensible value. At least the output tube will be working in a sensible part of its characteristic.

In that case there really is little if anything to be gained by changing the output capacitor. Its value is so high that when feeding a regular 10K load its impedance is negligible and hence also its effect on the signal will be negligible. I recommend you check out the section on coupling capacitors in Doug Self's book.

Cheers

Ian

Thanx!

Epcos, Panasonic, Nichicon, Rubycon are brands I would prefer in this position.  C5 and C8 should be rated for 250VDC, for 105 degC if possible. I will suggest you also to replace HT power supply capacitors with 47u/350V verisons. Be aware of limited space inside the box. And stronger (current wise) wall wart would be a good investment.
I hope you already  read JCM's posts on Tape Op and GL threads.

tonedude said:

I would like to upgrade capacitors C5 and C8 in the EH 12ay7 preamp but wounder what brand and type to select?

Click to expand...

Panasonic any 105 degC series