Ampeg M15 Big M Cap Can question...

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Ampeg M15 Big M Cap Can question...

Postby giantsteps on Tue Feb 07, 2012 6:49 pm

Hey guys,

One of these came into my shop for a refurb/repair and it's obvious that someone else has been in there before. The Cap Can that is currently in the amp is an older one with a value of the 40uF 100uF 450V variety. From the schematic I'm assuming that it should be 20uF 20uF 30uF 450V. There is also an axial 30uF 500v inside the chassis (that isn't there in any of the gutshots I've seen from around the web.) Before I go tracing to see which cap the previous repair person replaced with what, is there any reason I shouldn't go back to the stock 20 20 30 configuration? Are the higher capacitance values a commonly done mod on this model?

Thanks,

Chris
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Re: Ampeg M15 Big M Cap Can question...

Postby Baron Von Machinenmann on Wed Feb 08, 2012 12:19 am

Welcome aboard! :cheers:

No reason not to restore it to stock values, the cans are available from AE or fliptops. Guys usually increase the capactance to get more lower end and less breakup, but IMHO that amp in stock from is a tone monster.

http://www.tubesandmore.com/scripts/fox ... CAPACITORS

http://www.fliptops.net/catalog/index.p ... 3640d00d16

Got any pics? :thumbsup:
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Re: Ampeg M15 Big M Cap Can question...

Postby giantsteps on Wed Feb 08, 2012 3:03 am

Thanks Baron. I had a feeling that the three large filter caps were meant to be in the can but I wanted to check and make sure. I'll take a couple of pics tomorrow when I start working on it. The cab is pretty rough, but there is a nice jensen 15 incher in there...

Chris
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Re: Ampeg M15 Big M Cap Can question...

Postby giantsteps on Thu Feb 09, 2012 6:10 pm

Here are a couple of gutshots of the amp...The big blue cap is a 30uF...that at least matches the schematic. The bypass caps in circuit are also stock value...

The ones that do not match are the 80uF and 20uF in the cap can (should be 20/20), and the 100uf going to the 6l6s...hell of a lot more filtering than stock. I think I'm going to go back to stock values on this one...

Chris

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Re: Ampeg M15 Big M Cap Can question...

Postby Baron Von Machinenmann on Fri Feb 10, 2012 12:11 am

That's a keeper, love them fat sounding octal preamp tubes, my oldest Gemini 1 ('64) has those and definitely has the "it" factor. :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby giantsteps on Tue Mar 27, 2012 9:00 pm

Thanks for all the help and suggestions. Rebuilt the ground scheme in this amp and changed a couple of plate resistors to stock values (interestingly enough, the stock value in the amp on the phase inverter didn't match the schematic inside of the cabinet. After a good amount of testing and burn in, this amp is quiet and clean...and back to the customer...

Unfortunately had to break the news to the customer that the 15" jensen inside is not only not original, it's beginning to fail and is the wrong value for the amp (4 ohm vs 8.)

Chris
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Re: Ampeg M15 Big M Cap Can question...

Postby P-Dawg on Thu May 10, 2012 11:50 pm

I just scored one of these on fleabay needing repairs. The price was right and it looks pretty good. As it happens I have a power transformer that'll drop right in.

I've got one here in the shop for a look over, all original down to the tubes. It was a good opportunity to document one that had never been hacked so I got out the macro lens and went ot town. I finished up with a raft of voltage measurements. :cheers: :cheers: :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby Baron Von Machinenmann on Sun May 13, 2012 7:36 pm

PICS!!!!!!!!!!!!!!!! :P :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby P-Dawg on Mon May 14, 2012 1:21 pm

Baron Von Machinenmann wrote:PICS!!!!!!!!!!!!!!!! :P :cheers:


I promise, I promise.

The M15 is supposed to arrive here tomorrow and if somebody will tell me how to link photos to this site I'll do a full on photo shoot. :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby Baron Von Machinenmann on Mon May 14, 2012 5:03 pm

:cheers: :rawk: :thumbsup:
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Re: Ampeg M15 Big M Cap Can question...

Postby P-Dawg on Wed May 16, 2012 12:50 pm

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Here they are. The PT is defunct and the control panel has a dent in it that'll need hammering out. :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby Baron Von Machinenmann on Wed May 16, 2012 5:40 pm

Damn skippy amp there Dawg, any idea which (brand) pt you'll end up with? Is there a usable schematic inside of the rear panel?
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Re: Ampeg M15 Big M Cap Can question...

Postby P-Dawg on Wed May 16, 2012 9:31 pm

Baron Von Machinenmann wrote:Damn skippy amp there Dawg, any idea which (brand) pt you'll end up with? Is there a usable schematic inside of the rear panel?


The schematic is in the inside. The commonly available Joe Piazza schematic contains a number of errors.

As it happens I have a NOS Stancor power transformer that is just the ticket for this amp, already swapped the bells over. I ordered a JJ LCR style 40-20-20-20 can cap for this beast as it is significantly less cash than the Mallory FP types. I've got to take the pots out and straighten out the panel with a little bodywork.

If it sounds anywhere near as good as the other one that was around here I'll be a happy guy. :cheers: :cheers: :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby P-Dawg on Thu May 24, 2012 3:19 am

I got the M-15 running today. The Stancor iron worked out just right, with a plate voltage of about 400 using a 5AR4 rectifier. Pounded out the dents in the panel and although not perfect it's a lot better. So far so good, after a good cleanup the next project will be to change the cap can and maybe sub a larger output transformer-I have some recently acquired output iron that should fill the bill quite nicely and add some more muscle.

It's always a good idea to grab stuff when you see it. That power transformer was acquired a couple of years ago in a box of miscellaneous stuff at an auction for a buck. It was shopworn but had never been installed.

I'll post more pics when it's complete. :cheers:
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Re: Ampeg M15 Big M Cap Can question...

Postby Baron Von Machinenmann on Thu May 24, 2012 10:19 am

Cool, glad you got her sorted out. Any chance of you posting a nice sharp pic of that schematic? I've been photographing any I can find (geminis, jets, rockets etc) as I never was 100% confident in the commonly available JP "drawerings"...... :wink:
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