marshall avt50h schematic?

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#4
Hello! I'm new to these forums, but I got here via Google, because for a while I am searching for schematics of Marshall AVT amps. I'm mainly very interested in how they designed the preamp with the 12AX7-valve. I was wondering if you would send me the schematic mentioned in this thread (or any other AVT).

Greetings from the Netherlands,
Mark de Ruiter
 
#7
Don't know if you have been here yet but you could try these sites, they might help as they have an astounding set of schematics for everything under the sun:

http://www.drtube.com/guitamp.htm

http://www.freeinfosociety.com/electronics/schempage.php?cat=1

http://blueguitar.org/schems.htm#Marshall

You may not find the actual schematic for your own amp as it is current, they tend to prefer the older valve models, (as most of us do 😉 ), but I am betting if you are flexible in your thinking you will be able to get somewhere with what is there on the older babies.

The reverb section in your preamp is no doubt one which is shared by a number of models past and present. While not exactly the same in all cases you will probably find one where things are pretty much similar to your own.

If you can post a few of the current symptoms, (burnt components, strange noises, silence?), assuming you have the reverb unit back in place and hooked up correctly again of course, someone may be able to advise. If you chased through the section around the reverb connections on the PCB and posted a pic of the schematic you find it would be even easier to help. 😀
 
#8
On the Dr Tube site there are some of the Valvestate amps with their reverb sections. These will give you a first idea of how things may be done.

http://www.drtube.com/marshall.htm#VS1

or as one particular example you will find there:

http://www.drtube.com/schematics/marshall/8280-61-02.pdf

which is one standard type circuit block to drive the reverb.

If it is just the reverb section at fault, all that may be necessary could be to renew any semiconductors around the unit. These need not be exact replacements. Despite "modern thinking", (read "common knowledge", ie there is no proof of it but we just "know" it to be the case), there will be very little change in sound by replacing with a close equivalent, as long as the pinout is a match too of course. Guitar amps played with a degree (?) of distortion would show more change of tone by using a different plectrum than by a swap to a similar IC or transistor!
 
#16
Nicely surprised!!!

Mr McCallum... I Don't know who you are,but I want to assure you that
, without your help, I never could solve my problem. Thanks, and thanks, and...thanks again!!!
At your service
Ulises.
P.S. : If there's something I can do for you, you just have to
ring the bell...¡I'll be there!
 
#19
for those of you that have AVT-50 amps, here's a service tip:

problem intermittant +5V supply to preamp and logic (DSP) boards.

cause: loose or oxidized low voltage power supply cable connector.

fix: unplug and re-plug the connectors on the white ribbon cable going from the power supply board to the preamp/DSP.
 
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