Advice on Repairs for Audio Research VT100 Mk II

According to the schematics the VT 100 MKII is a fully balanced design. The offset between pos and neg branch needs to be set to 0 and that's taken care of by some ss circuits between the 6922 (some adj. can be made with RV1/RV2 trim pots).

The 6922 are double triodes and it's of course harder to match those tubes because you need a lot of them in order to find 4 tubes per channel where the two triodes in each tube are also about the same quiescent current. That makes it time consuming and expensive. In general Audio Research biases  their output tubes very hot and they need a lot of tubes to select from in order to reach those goals. That's why it is so expensive if you go to Audio Research for retubing.

Many things can go wrong if one tries to do this buying tubes (even matched) somewhere else unless one fully understands how this amps work. Schematics are available online.

To use the VT100 only makes sense IMO(considering the high cost) if one uses  a fully balanced system (at least preamp to amp).

 

Since you mention that it is your first tube amp I want to mention that hopefully you are aware that you should not turn a tube amp on and off and back on quickly without giving the capacitors a couple minutes to discharge.  That can lead to problems such as you describe.

I think I did do that a couple times because I was following another rule that someone told me: always turn on the source (DAC/pre-amp) before turning on the amp. Once or twice I forgot about this and turned on the amp first, so then I turned it off, turned on the DAC/pre-amp, and then turned the amp back on. Doh. 

I had a VT 100, MK III and loved it.   So my comments are based on experience with that particular iteration.
 

Probably, you’ll want a tech to replace the resistor and test to ensure that everything is copacetic.  
 

But it doesn’t take much skill to replace and bias the tubes yourself.  Bias adjustment instructions can be found at the Audio Research Database (arcdb.ws I believe), so you can read it and see how comfortable you are with the procedure.  
 

You can buy a package of matched tubes specifically for your amp at the Tube Store.  They have good selection and pricing, and their customer service is excellent.

 

I used to retube and bias mine in about an hour.  It’s a wonderful amp and I’d hate for you to give up on it.

Hi Edward. There is a lot of wisdom here on this forum.

 

The first question I would be asking myself is “am I in love with this amplifier”?

 

The first question I would be asking myself is “am I in love with this amplifier”? If the answer is yes, it makes me very happy and I do not want another then proceed with your repairs.
 

The amp is worth about 2500 US in full working condition, and probably about $1000 US for parts or not working. If you have the budget, I would consider selling the amp what I could get an upgrading to a more modern ARC product.

 

The amp is worth about 2500 US in full working condition, and probably about $1000 US for parts or not working. If you have the budget, I would consider selling the app for what I could get an upgrading to a more modern ARC product.

 

 ARC used resistors as fuses for years. I have had a personal experience with my VT 130 blowing up resistors and causing me much frustration.

 

 ARC used resistors as fuses for years. I have had a personal experience with my VT 130 blowing up resistors and causing me much frustration.

If you were working inside a tight budget repairing the amp would be a lot cheaper than buying a newer one. 
 

Tube gear reminds me a lot of being a Ferrari owner. They’re not that expensive to buy but they are terribly expensive to own. That being said there is nothing like them! To the uninitiated or uninformed that statement would make zero sense whatsoever.

another consideration is replacing the resistors your self. That is what I did, and I had a lot of fun working on my ARC amp with the understanding that if I failed, I was screwed anyway, learning about the amplifier and its components was a wonderful journey for me. Your amp is old enough and inexpensive enough to afford the education. 
 

Another consideration is the mess Europe is in right now facing a cold winter with limited energy. You may be able to buy a much better amplifier at a deep discount in February or March.

 

Another consideration is the mess Europe is in right now, facing a cold winter with limited energy. You may be able to buy a much better amplifier at a deep discount in February or March.

 

I understand your frustration as I have been exactly where you are. At first I was very unhappy about it, but it really became quite the adventure and I am better off for it.

 

I hope.  and I am better off for it.

 

I hope this bit of information is helpful.

 

 

@77jovian

The ARC VT100 MK III does not require the 6922 input and driver tubes to be biased. Only the output power tubes need to be biased...

It can take hours to bias the 6922 tubes in a VT100 or VT100 MK II...

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