web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

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web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby dai h. » Wed Apr 01, 2009 12:08 pm

(sorry if this isn't new!)

some shots of chassis

SERVICING OF A WALLACE AC 3500 XT Mk IV AMPLIFIER HEAD

http://www.chambonino.com/work/miscguitar/misc22.html
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby Brian Wallace » Wed Apr 01, 2009 9:04 pm

New one to me. Thanks for posting this one. :wink:
Remember....You can fix it with a little extra energy and a positive attitude. ;)
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby matabass » Thu May 21, 2009 8:24 am

Hi all... new to the forum. I have an AC3500 XT MkIV that has been modded to MkV (in 1973). Anyone know what that mod is? I assume it was done by Ted Wallace.

Will
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby dai h. » Fri May 22, 2009 9:27 am

hi, welcome. :) If you can post some pics of the internals, Brian might be able to help. As far as I know, he has some familarity with the amps, and even if there isn't any specific knowledge available, looking at the circuitry should give an indication of what it is.
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby matabass » Thu Jun 04, 2009 6:20 am

ok... thanks... its with someone having a cap replaced at the moment but i'll get some pics up soon...
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby matabass » Fri Jun 12, 2009 5:29 pm

Hello again! I have got my amp back... sounds amazing! I have just had a look in the cab (also Wallace) and it contains a pair of Goodmans Audiom 12-P @ 8 ohms, 50 watts. They are wired in series so should I set the amp impedance to 4, 8 or 16ohms for the best sound/volume? Thanks, Will
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby matabass » Fri Jun 12, 2009 5:39 pm

Some pics... :D Any info on this is welcome...
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Re: web page SERVICING OF A WALLACE AC3500 XT MkIV HEAD

Postby dai h. » Sun Jun 14, 2009 1:57 am

matabass wrote:Hello again! I have got my amp back... sounds amazing! I have just had a look in the cab (also Wallace) and it contains a pair of Goodmans Audiom 12-P @ 8 ohms, 50 watts. They are wired in series so should I set the amp impedance to 4, 8 or 16ohms for the best sound/volume? Thanks, Will


Two 8 ohm speakers wired in series is 16 ohms, so to match the output and speakers the amp should be at 16 ohms. There are cases where you can mismatch but I think it would be best to be certain since it seems in some cases (some Marshalls seem to be sensitive for some reason) mismatching can lead to damage. If you go lower it's harder on the tubes (more current--plus I would think the output transformer as well), and higher is harder on the insulation (stuff coated on the copper magnet wire inside the output tranformer) since (I think) the primary (signal) voltage goes higher (but less current). (Could be some old Marshalls had borderline adequate thickness of wire which melts with downward mismatch and higher currents, more heat, more output). Different from this apparent sensitivity to mismatch is (for example) my Mesa/Boogie .22+ where it actually states in the instructions that it is acceptable to mismatch (the stock single spk. is 8 ohms and it's okay to connect to the 4 or 16 ohm output jacks). And FWIW (while it's been quite a while since I've used my .22+) from what I remember experimenting with mismatching, it wasn't anything gargantuan in (tonal) difference. I think by the time the signal gets to the output section the preamp shaping has already had its "stamp" (frequency accentuation, de-accentuation, gain, etc.) impressed upon the sound.

Also, thanks for uploading the pics. I'm sorry I don't know much about them to tell you anything, but from what I can see the workmanship looks outstanding. Probably more thoughtful (and thought out) than in Marshalls. Kind of reminds me of an old Mullard hi-fi DIY article (seen somewhere on the internet) in the "style" of the build.
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