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All,
Anyone running their MK3 in pentode mode ? I ordered an SDS cap board (but don't have it in my hands yet...) so I am not sure where I can get the voltage needed for the screen...Just am curious if anyone else pulled it off.

Thanks,
Steve

SteveH wrote:All,
Anyone running their MK3 in pentode mode ? I ordered an SDS cap board (but don't have it in my hands yet...) so I am not sure where I can get the voltage needed for the screen...Just am curious if anyone else pulled it off.

Thanks,
Steve

I do not know why you would wish to do this. Pentode mode has a higher output but more distortion than UL mode.

The easiest way is to tap off the B+ and drop the voltage with a resistor, but this is not advised. Screen supplies should be regulated. The screen supply should - if possible - have its own separate transformer winding.



Look at the screen supply in the above image. The B+ is dropped by a 10k/30W resistor then it goes through 2 diode tubes.

Thanks for the help, it was more of a curiousity...

Interesting schematic ya have there...I just so happen to have two MI-12188A's sitting in my garage...You have any additional info on them ?

SteveH wrote:Thanks for the help, it was more of a curiousity...

Interesting schematic ya have there...I just so happen to have two MI-12188A's sitting in my garage...You have any additional info on them ?

Yes, a restoration guide. I would kill for those amps, so do you give out your address. They go for ridiculous prices on ebay.

http://www.montagar.com/~PATJ/mi12188a.htm