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In Reply to: RE: McShaning the Mac mc225 posted by sam@edelmannpgh.us on December 26, 2014 at 08:26:47
Here is one of the first Mc225s I McShaned.I put in a combo of Vit Q and K40s but to tell you the the truth,the original brown CDE mylars that are in the amp are fabulous and I leave those in as they are a true film and foil..The Sherwood also uses these same caps..The only caps you need to change are the bumblebees..Those are the .047 at 600v and those have to be paper in oil.The input cap I use a film and foil on.
"
Follow Ups:
Mike,
I went to the parts bag on this amp, and the .047 600vdc caps I found were Sprague, black with a red circle. I suspect these are not the original, and not the ones you were speaking of, but thought I'd ask.
Thanks,
Sam
The ones you put in were black beauties and they are actually a great cap.I just prefer a k40 there in that position.At least the black beauty is a paper cap.
"
I will try the CDE Mylars and see how they sound.
Meanwhile, I bought some 7591's from Jim. Don't remember the brand, but they had larger bottles. The application was for a Fisher 500B, and Jim suggested adding a small resistor to ground for these tubes. As I may use them in the Mac, do I need to add the resistors there too?
Sam, that was NOT what I recommended! I recommended a change in the value of the grid "leak" resistors since the 330K resistors used in the Fisher were above the spec for the tube, and the EH tubes you got (and all other modern 7591As) are more sensitive to this resistor value.
That resistor change is not required on the 225 since the stock values are in spec by a comfortable margin.
Also, as Mikey mentioned you CAN fit K40s to the 225!
Jim,
Sorry. I obviously misspoke. It had been a number of years since I did the Fisher. I will take another look at the k40's with the provided picture.
Thanks,
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