6C45Pi Microphone Preamp

[MIKET]

This tube should make a great front end with a good input transformer.

Here is my 1st cut at a 6C45pi Microphone Preamp
http://home.midmaine.com/~talbot//MIC_Preamp.jpg
Your comments are encouraged.

 

[Brian Clark]

With a cathode resistor of just 7.33 ohms (3 x 22R in parallel) and 200V across the 6S45P you are going to get a LOT more current pulled than 17mA!

I have found it sufficient to clip the socket tag corresponding to the second grid pin and use just one grid connection with 100 - 150 ohm carbon comp grid stopper. Also I only connect to one cathode pin, letting the others "go hang".

I would suggest you try just 100V B+ and use a 1.2V battery to bias, either a Lithium Anhydride in the cathode (which will be constantly charged) or any similar voltage battery "ars*-up" in the grid circuit.

My experience with this valve type is restricted to power amp applications I'm afraid so may not be relevant to your application 😉

Brian

http://www.sempermusica.com

 

[MIKET]

OOPS!!!!!!!!!

I need to not stay up so late.
I made a mistake on the cathode resistor.
Here is the corrected diagram, it's also fixed for the link.

 

[Brian Clark]

Aah, that's better! 🙂

Should fly.

Give it a go and let us know how it works out.

Brian.

 

[Eli Duttman]

FWIW, Bruce Rozenblit uses a 6c45pi in cascode as the 1st gain block in his phono stage kit. If it works for phono, it will work for a microphone.