AVT100 mains fuse blows - Circuit anyone?

David F · 12-03-2008, 05:29 AM

First time on the site so apologies if there is already a link for this. I have just bought a faulty AVT100 which immediately blows the mains fuse. I suspected one of the bridge rectifiers short/leaking but this is not the case. The mains TX is ok and none of the electrolytics appear leaky. The problem is on the 32-0-32v line and I suspect the output transistor but would like to find a circuit to confirm-have looked on Marshall Amp Heaven Schematics, Guitar Amp schematics and Prowess Amps sites without success; Does anyone know where I could get one or know if this is a stock fault. Many thanks, David.

JohnH · 12-03-2008, 06:04 AM

Ive never seen AVT schematics, but Dr.Tube. The specialist in the repair and modification of tube amps. Sale of tubes and components. have the ealier valvestates that might be similar
John

David F · 12-03-2008, 06:21 AM

Hi John,
Thanks for the rapid reply! I've already had a look at some Valvestate circuits on the Marshall Amp Heaven site (they are readily available and free whereas you appear to have to buy them on Dr Tube?) but they appear quite different so am still searching.
Thanks again,
David

JohnH · 12-03-2008, 01:37 PM

OK, but drtube schematics are also free. eg, maybe you already have the Mk11 Valvestate circuit, but its this:
http://www.drtube.com/schematics/mar...v100-62-02.pdf
So are the AVT equivalents very different? - Im surprised if they reinvented the power stages for the next model.
John

David F · 12-04-2008, 06:59 AM

HI John,

Looks like I jumped the gun regarding charging for their circuits at Dr Tube - I had previously copied the url www.drtube.com/schematics and just got the message "Unauthorised to access schematics" so assumed they were chargable - WRONG!

The output of the AVT 100 is a power i.c. TDA7293 as opposed to transistors in the VS100 so that circuit doesn't help. When looking at the output i.c. circuit board, I noticed it is labelled as AVT50 and not AVT100. The previous owner said that it has not been repaired before so I think I'll try Marshall for some more info although I'm not sure how user friendly they are.

Thanks,

David

12-03-2008, 05:29 AM	#1 (permalink)
David F Junior Member Join Date: Nov 2008 Posts: 3	AVT100 mains fuse blows - Circuit anyone? First time on the site so apologies if there is already a link for this. I have just bought a faulty AVT100 which immediately blows the mains fuse. I suspected one of the bridge rectifiers short/leaking but this is not the case. The mains TX is ok and none of the electrolytics appear leaky. The problem is on the 32-0-32v line and I suspect the output transistor but would like to find a circuit to confirm-have looked on Marshall Amp Heaven Schematics, Guitar Amp schematics and Prowess Amps sites without success; Does anyone know where I could get one or know if this is a stock fault. Many thanks, David.

12-03-2008, 06:04 AM	#2 (permalink)
JohnH Senior Member Join Date: May 2008 Location: Wollongong NSW Posts: 778	Re: AVT100 mains fuse blows - Circuit anyone? Ive never seen AVT schematics, but Dr.Tube. The specialist in the repair and modification of tube amps. Sale of tubes and components. have the ealier valvestates that might be similar John __________________ DSL401 8412 cab Crate Powerblock 1 x 12 Vintage 30 cab '76 Shergold Masquerader '93 Les Paul Studio '83 Roadstar

12-03-2008, 06:21 AM	#3 (permalink)
David F Junior Member Join Date: Nov 2008 Posts: 3	Re: AVT100 mains fuse blows - Circuit anyone? Hi John, Thanks for the rapid reply! I've already had a look at some Valvestate circuits on the Marshall Amp Heaven site (they are readily available and free whereas you appear to have to buy them on Dr Tube?) but they appear quite different so am still searching. Thanks again, David

12-03-2008, 01:37 PM	#4 (permalink)
JohnH Senior Member Join Date: May 2008 Location: Wollongong NSW Posts: 778	Re: AVT100 mains fuse blows - Circuit anyone? OK, but drtube schematics are also free. eg, maybe you already have the Mk11 Valvestate circuit, but its this: http://www.drtube.com/schematics/mar...v100-62-02.pdf So are the AVT equivalents very different? - Im surprised if they reinvented the power stages for the next model. John __________________ DSL401 8412 cab Crate Powerblock 1 x 12 Vintage 30 cab '76 Shergold Masquerader '93 Les Paul Studio '83 Roadstar

12-04-2008, 06:59 AM	#5 (permalink)
David F Junior Member Join Date: Nov 2008 Posts: 3	Re: AVT100 mains fuse blows - Circuit anyone? HI John, Looks like I jumped the gun regarding charging for their circuits at Dr Tube - I had previously copied the url www.drtube.com/schematics and just got the message "Unauthorised to access schematics" so assumed they were chargable - WRONG! The output of the AVT 100 is a power i.c. TDA7293 as opposed to transistors in the VS100 so that circuit doesn't help. When looking at the output i.c. circuit board, I noticed it is labelled as AVT50 and not AVT100. The previous owner said that it has not been repaired before so I think I'll try Marshall for some more info although I'm not sure how user friendly they are. Thanks, David

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