Schematic of Audio Research VT 100

[Alex helge]

Dear members

here the Schematic of VT 100
http://www.drtube.com/audioamp.htm#AR

and the Bias adjustment of VT 100

http://mycollins.net/audio/artube1.html

Best regards Alex

 

[PTSOUNDLAB]

Hello,

this link is dead http://mycollins.net/audio/artube1.html have you more informations ?

Do you know the OUTPUT TRANSFORMER specifications ?

Thanks

Pascal.

 

[toprepairman]

Hi Alex.
Don't suppose you have the VT100 power supply section schematic?
Regards
Henry

 

[toprepairman]

Hi again, found it now so no need, thanks.

 

[alex mm]

...... maybe will help this link ARCDB - VT100 😉
Alex.

 

[toprepairman]

Great link, thanks Alex.
This amp has a problem in the 320v regulator.
Started with a big bang and puff of smoke.
The 4A power fuse blew, and the 10R 0V to ground resistor blew.
Now it runs but puts 420 onto the 320V rail.

 

[smoking-amp]

Looking at the pictures of the MKIII versus the MKII, the MKIII has got significantly smaller OTs and a smaller power xfmr. It's lost half the input/driver tubes and no heatsinks are visible for the CCS's anymore. Cost cutting with a much higher price?

 

[toprepairman]

It could be a problem of perspective, the pictures are from different distances, I suspect the transformers are the same.
Back to the fault. In this amp (a Mk 2) the resistor R50 has been replaced by a 3 legged fuse (a transistor of unknown type- numbers removed and replaced by paint colour code) and a couple of resistors. The fuse went short so forcing the 320 rail up to 420!
So an imperceptable performance 'improvement' compromised the reliability and could have caused some serious damage, when will they ever learn......

 

[kevinkr]

It's one of the reasons I stopped working on ARC amps - lots of complexity and owners who modded the amp or put poor quality KT88s in the amplifier resulting in a lot of collateral damage.. Not easy to get the parts out of their very thick PCBs either..

 

[rcbrds]

Back to the fault. In this amp (a Mk 2) the resistor R50 has been replaced by a 3 legged fuse (a transistor of unknown type- numbers removed and replaced by paint colour code) and a couple of resistors. The fuse went short so forcing the 320 rail up to 420!
So an imperceptable performance 'improvement' compromised the reliability and could have caused some serious damage, when will they ever learn......

I know this was a long time ago, but I'm going through the same problem on my VT100mk2 . Your post has been really helpful to this diy-er. I have 420v in the 320v. That started the same way with smoke, the main fuse and house section breaker all tripping or blowing. I have that 3 legged fuse where R50 is supposed to be. I had know idea what I was looking at until I read your post! Since the transistor is painted, it is ARC original. I don't understand why the schematic is incorrect. Thank you for your post if you are still around.