Schematic for Marshall AVT20 Needed

[padamiecki]

Hi
sorry guys to be slightly offtopic,
I just need a schematic of a combo Kustom Arrow 16,
and would not set new thread for it,
could anybody help?
please,
Thank you in advance!
P

[earache60]

Hiya

May I please request a copy of the Marshall AVT20 schematic? I am newly registered here and so am under surveillance or some euch thing...

[marcofry]

once you can use the email button email me and I will send you a copy

[earache60]

Hi


Thank you for your kind offer. I found an earlier thread where somebody requested and received a schematic for a similar amp (Marshall AVT 50) so I e-mailed the replier in that thread and received the schematic from them (thanks tmenzo!).

Could I ask an opinion on a possible mod to the AVT20? I find that the amp is very shrill at higher volumes, what would be the component(s) I could change in the tonestack to help the situation?

[krizza]

May I also get Marshall AVT20 schematic? I am too under moderation...

[Enzo]

It never ceases to amaze me the memory of the internet. I posted about having certain Marshall schematics several years ago on this board and I still get several requests a week for them.

[eweege]

Please count me in too. I tried emailing to "doctor" but can't email yet as I am still in "moderation" mode.

I need a schematic for the AVT-20. I found a burnt resistor at location R53. The problem I was having is that the amp was motor-boating when turned on.

Anyone have any ideas on a) what caused the resistor to overheat, b) where I can find an R53 replacement resistor, and c) where I can find a replacement metal post for one of the speaker wires to connect to? One appears to have snapped off during as I was removing the amp board assembly.

Thanks in advance.

Regards,

Eric

[eweege]

I found a schematic for the AVT-50 but not for the AVT-20 yet (still in moderation mode). The AVT-50 shows R53 as being a 22k ohm resistor (1/4 watt?). Does anyone have any root-cause experience for these blown resistors and/or know how similar the schematic circuitry is between the AVT-20 and 50? I guess I'll check for any other blown/shorted caps, diodes, ICs, etc in the immediate R53 circuitry area while I'm waiting for email approval..

Thanks,

Eric

[marcofry]

the avt-50 schematic is DIFFERENT from the avt-20 by miles...the avt-20 schematic has a 10ohm 1/2 watt resistor in r53...according to the tda 2050 data sheet it helps prevent oscillation/feedback? c71 is associated with it ...c71 is .22microfarad ...when r53 toasted it melted c71 as well...I know for a fact that letting the amp feedback alot will toast this resistor.

[earache60]

Hello Again

Would anyone care to make a suggestion as to how to make this little amp less shrill (see my post above). Would socketing the TL072 chips and trying different opamps there make any difference? How about the tonestack-is there any component changes that would help? Finally would changing out the 12AX7 for a 12AT7 or 12AU7 help matters any?

Thanks all for your time and efforts

earache60