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In Reply to: RE: Rebuild of MC30s posted by Lee of Omaha on April 29, 2016 at 17:53:58
the biggest thing that benefits these is the film cap power supply and a choke.I use the .32hy or the .5hy and of course the common tie point ground.
The 6CG7 is a nice improvement as well however,not everyone wants to do that so your alternative is to use a 12BH7 or make an adapter.The film cap supply is monumental in in Mac amps especially with the tube rect.The choke you can bolt on to one side of the power trans and goop the other side so you don't make a hole in the chassis.
A friend you get for nothing,an enemy has to be bought
Edits: 04/30/16Follow Ups:
Mikey,
In the photo, is the choke ( looks like the nicely inexpensive $10.00 Traid C-40X, 320 mHY at 600 mA., 10 Ohms DCR ) the first component the rectifier's output "sees", OR, is it seeing a film cap as the first device??
In other words, are you
(a) Rectifier tube, sub-critical choke, 50 uF film cap OR, are you
(b) Rectifier tube, 50 uF film cap, sub critical choke ???
Q1 : Did you try it BOTH ways above??
Q2 : If so, what did you hear / think ??
Q2 : Ever able to try L1/C1/L2/C2 in a Mac30, with Ls and Cs being EQUAL and small in value...320 mHY and 50 uF ?? Ever HEAR that ??
I haven't tried a second choke but I am ever so grateful for your .32hy low resistance choke.Believe it or not,you can take out the 150 ohm and put the choke in its place and it raised the B+ exactly 3.1dc which is nothing but the performance gain was monumental.Doc Hoyer also uses that choke in his Mc30s and you can use it in the Mc60s he says.
A friend you get for nothing,an enemy has to be bought
Edits: 04/30/16
There are a couple of things that are better when you did that.
First, you eliminated 140 Ohms of series resistance to the Finals, by removing a 150 Ohm series-R ( adding resistances, is always a BAD idea to the Finals ) and you replaced 150 Ohms with a 10 Ohm choke.
Yes, that will wake up the amp, dynamically, nicely.
The second thing you MAY have done is, IF you placed the 320 mHY L right after the rectifier, and had the 50 uF DC LINK Panasonic cap after the L : you went from a "C" input filter to an "L" input filter, that the tube rectifier was working into.
It is always best practice for the tube rectifier to "see" an "L" as the very first part after it. It certainly need not be " critical in inductance " either. :-)
If you hadn't done that, ( L first ) you should have, and LISTENED to that for your own edification. ( Nice 25 cent word .)
Mikey, you are AOK !!!!
Jeff Medwin
I use a 50uf panasonic film there.
A friend you get for nothing,an enemy has to be bought
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