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Topic: Need clarification on "Healy Mod" |
Mark Herrick
From:
Bakersfield, CA
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Posted 22 May 2005 11:20 am |
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I know I have been asking a lot of questions here in "Electronics" lately, but anyone who has done this mod can perhaps help me.
Some quotes from the post that JB Arnold made a while back:
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| First, in addition to changing all of the caps, you will want to change all of the plate resistors for non-inductive metal film versions. Also change all of the cathode resistors and use tantalum capacitors for the bypass caps… |
By “all” of the caps, does he mean the filter caps as well or just the signal caps? (My filter caps have been replaced recently.)
For the cathode resistors is he specifying metal film resistors for those as well?
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| There are a few other things but this is the main idea. |
What are the “few other things”?
And finally:
Are the bypass caps the white cylindrical ones that are rated 25mfd/25V? The two connected to V1A and V2A pin 3 have a 1.5K resistor in parallel and the one connected to V1B/V2B pin 8 has an 820 Ohm resistor in parallel.
The closest value tantalum caps I can find are either 22mfd or 33mfd at 25V. Can I use either of these and what difference could I expect due to the difference in value from the original 25mfd/25V?
Thanks for the help!
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Jon Light
From:
Saugerties, NY
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Posted 22 May 2005 12:36 pm
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Mark---when I was doing work on my amps last year I had my head into it pretty intensely but a whole lot of what I had a grasp on has since evaporated so I will stay clear of most of this so as to not give bad info. But what I will comment on:
Brad Sarno was awesomely helpful and generous enought to provide me with a couple of tantalums. They were 22's. So that should answer that question.
A big problem with being a hack is that there is too much time elapse during making these changes to effectively a/b your experiments but.....my opinion was that the tantalums made my Dual Showman Reverb a little too hi fidelity. I discovered a preference for a slightly grainier sound so I removed them. Wish I could give it a true blindfold a/b test to confirm my impressions. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 22 May 2005 4:39 pm
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I agree with Jon. I tried the Healy tantalum approach. The Healy recommended tantalums are only for the cathode bypass caps on the preamp tubes. I found them too crisp and glassy on top, so I went back to the Sprague Atom electrolytics. Those are pretty much the standard these days for good cathode bypass caps. I can see how Garcia's Twin may have done well with those for that real hi-fi tone, but it was just too much crisp highs for my taste on steel.
Brad |
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Mark Herrick
From:
Bakersfield, CA
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Posted 22 May 2005 9:31 pm
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Good to know about the tantalums and Atoms for the bypass caps. I think I might like to try the Angela caps I mentioned in the other thread instead of the Orange Drops.
I was doing an inventory of all the caps in my '74 Twin and noticed that there is one cap, between V4B and the master volume control that is rated .015mfd/1600V.
Is this voltage correct? The closest value I found at Antique Electronic Supply for the 1600V cap was .01/1600V. Would this work?
All of the other caps are 600V, except for a .1mfd/200V cap in the phase inverter circuit. I can't find any 200V caps at AES. Can I use a 400V or 600V cap instead?
And should I replace ALL the original blue caps (and one brown) with the Angela caps or just certain ones? (They are pricey at $6 each.)
Thanks for the help!
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[This message was edited by Mark Herrick on 22 May 2005 at 10:34 PM.] |
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Blake Hawkins
From:
Florida
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Posted 23 May 2005 5:20 am
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Mark,
The schematic I have shows that the coupling cap from the master volume to V6A (12AT7)
is .01 mfd, 600v.
Perhaps what you have is not the original cap but a replacement.
The .015 1600 volt caps were originally sold for use as "buffer" caps in tube type auto radios.
It's OK to replace a 200 volt cap with a 400 or 600 volt cap. You can go higher on the voltage but not lower.
Blake |
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Mark Herrick
From:
Bakersfield, CA
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Posted 23 May 2005 9:22 am
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The cap I am seeing looks like it is part of the wiring to the push-pull part of the master volume control.
If you have the "CBS 100 Watts RMS Amp W/ Reverb and Vibrato" schematic, look to the left of the V6A position and you'll see the part I am talking about; just to the left of the 12K resistor.
Here's the schematic:
CBS 100 Watts RMS Amp
So, do I need to replace ALL of the "blue drop" caps or just some of them?[This message was edited by Mark Herrick on 23 May 2005 at 10:22 AM.] |
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Blake Hawkins
From:
Florida
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Posted 23 May 2005 12:24 pm
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Ok, Mark, thanks for the diagram.
I see the .01 cap you are talking about.
Still don't see any reason why that cap should be higher than 600 v.
Perhaps Ken Fox can chime in here as he has done more of these amps than I have.
Blake |
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Ken Fox
From:
Nashville GA USA
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Posted 23 May 2005 1:40 pm
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600 VDC is fine there. Also the old Blackface used a .001, a nice mod if you are getting muddy bass response.
I would use the Sprague/Atom 25uf at 50VDC. It is near identical in sixe tot he old white 25/25 caps.
The blue drop caps are pretty good sounding caps. I would only replace them if they were leaking any DC. [This message was edited by Ken Fox on 23 May 2005 at 02:42 PM.] [This message was edited by Ken Fox on 23 May 2005 at 02:43 PM.] |
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Mark Herrick
From:
Bakersfield, CA
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Posted 23 May 2005 4:48 pm
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OK, I guess I'll leave the coupling caps alone for now and replace the bypass caps with the 25/50V Atoms. (But if I wanted to just TRY some of those tin foil caps, where would be the best place in the amp to try them?)
Are there any other caps I should look at replacing; like the 80/75V on the rectifier board. Seems like I've heard that one can be replaced with a 100/100V. Would this do anything to the bias voltage?
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Mark Herrick
From:
Bakersfield, CA
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Posted 25 May 2005 1:32 pm
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OK, I got the 100/100V replacement bias supply cap and some 25/50V bypass caps.
I couldn't find the 5/50V for the V5B bypass cap (or any 5/xxV). I did find a 8/150V cap. Can I use that in place of the 5/50V?
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Ken Fox
From:
Nashville GA USA
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Posted 25 May 2005 4:09 pm
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| DFender often used a 25uf at 25VDC for the tremolo tube, with no other changes around the tube (resistors values were the same). I am building a vibroverb clone from a Bandmaster reverb now and had the same 5uf cap. I just used a 25uf at 50VDC. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 26 May 2005 7:40 am
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And don't forget "F.R.E.D's" if you want the best sound. At least, that's what the afficianados say!  |
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Mark Herrick
From:
Bakersfield, CA
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Posted 26 May 2005 1:15 pm
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Thanks, Ken.
Yesterday I replaced the bias supply cap with the 100/100V Atom and the plate load resistors for V1 with 100K Riken Ohm carbon film resistors. I still noticed the noise after I fired the amp back up. Then I changed the other 80/75V cap at the bias balance pot and the noise seems to have gone away. I'm warming it up again right now to see if it's still good. Haven't replaced any bypass caps yet.
?
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Mark Herrick
From:
Bakersfield, CA
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Posted 2 Jun 2005 12:53 pm
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I read the article about the F.R.E.D.'s.
Are they worth trying out?
Anyone around here used them?
I did some searching on the Fender forum and found the following exchange from 2003:
quote:
FREDs have uses, but can't see that power supply in a guitar amp is one. Just worked an Ampeg Vintage 33 with FREDs installed by owner-
NO IMPROVEMENT either of us can discern...
quote:
It seems Victoria is the one responcible for spreading this.
"As I mentioned in the article in the TQR, the installation of FRED's in the power supply of your amplifier will make the amp smoother and more musical. It's a mod that you will be glad you performed."
I have trouble understanding how it could improve tone. Perhaps the fact that they're selling them for $6 a diode has something to do with it?
quote:
This is more of a HI-FI AMP reason for using them, and where it came from in the first place I think. In that application, there may be a point.
Many of these ideas are taken out of context...
Still curious if anyone's tried them...
[This message was edited by Mark Herrick on 02 June 2005 at 03:21 PM.] |
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