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Old 30th April 2004, 01:21 AM   #1
MIKET is offline MIKET  United States
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Default 6C45Pi Microphone Preamp

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
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Old 30th April 2004, 08:37 AM   #2
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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

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Old 30th April 2004, 09:18 AM   #3
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Default 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.
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Old 30th April 2004, 05:30 PM   #4
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Aah, that's better!

Should fly.

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

Brian.
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Old 2nd May 2004, 12:08 AM   #5
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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.
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