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Advice on Repairs for Audio Research VT100 Mk II

Hi everyone,

I purchased a second-hand Audio Research VT100 Mk II for about EUR 2,500. After about 1 month, the fan died, which turned out to be faulty resistors near the fan. After about 6 months, there were some loud pops, and two more resistors were blown near one of the power tubes.

I sent it to the authorised Audio Research repair shop here in Germany and they quoted me the following for the repair work:

  • Replacing 10 Resistors 43100004 (at EUR 2.00 per resistor)
  • Replacing 10 Resistors 43100208 (at EUR 7.50 per resistor)
  • Replacing 8 6550 Tubes with J.J. Tubes (at EUR 20.50 per tube)
  • Replacing 8 6922 Tubes with J.J. Tubes (at EUR 83.95 per tube)
  • 13 hours of labour (at EUR 75 per hour).

For a total of EUR 1,905,60 plus 19% VAT, i.e. EUR 2,267. I pushed back and asked if really all of the tubes needed replacing and they said yes. I also pushed back on the price of EUR 83.95 per tube for the 6922 and they said that these tubes needed to be matched and therefore the costs include labour, shipping, and tuning/matching of the tubes.

Does that seem like a fair price for the work? I’m of course reluctant to spend on repairs what I’ve already spent for the amp itself. I’m fine with the price of the resistors, 6550 tubes, and labour but the price for the 6992 tubes seems too high. On the JJ Tubes website, these tubes sell for about EUR 20 a piece and they do not even offer matched sets of 6992. Do the 6992 input tubes really need to be matched?

Any advice or comments is much appreciated.

Thanks, Edward

edward78
fsonicsmith's avatar
fsonicsmith
931 posts
 

I agree with you Ralph and have a great Thanksgiving. As I said, ARC made some clunkers. Some of their amps were almost impossible to bias without taking to a good technician. And many dealers were forced to become proficient at replacing power tube resistors. I still maintain that for a large (by relative standards) tube amp specialist, their build quality is good and many have been reliable designs, again all things being relative. I know that your own tube amps are at the far spectrum of reliability. Kudos to you. At the end of the day, any electronic component will eventually need service unless pitched for something else, particularly tube amps. 

jond's avatar
jond
5,660 posts
 

I've never heard of biasing the small signal tubes in an amp just power tubes, that design seems very user unfriendly to me.

whart's avatar
whart
2,967 posts
 

@cleeds - thanks for pointing to the warranty, I obviously missed that. 

@jea48 raises a very good point about the caps. 

Sorry for your troubles, OP. It may be throwing good money after bad if that makes any sense. But perhaps worth asking about recap cost-- what else would normally go wrong in these? That old Dual 75a I have has no chips that I'm aware of-- but it was recapped a while ago and will probably need another go-over before I consider running it again. 

ghdprentice
6,358 posts
 

Op,

I definitely understand your dilemma. Honestly, I think the repair estimate is absurd. thirteen hours.

 

Also, calling ARC is in no way “going behind your repairman’s back”. That is an absurd quote. 

Audio Research makes some of the best amplifiers… regardless of the technology. You are talking about a 20 year old amp. A couple repairs and it is obviously got problems.

I would not loose faith on tube amps, or Audio Research for that matter. I have owned quite a few Audio Research components over the last forty years and have gotten. Nothing but incredible sound quality and reliability. I would get something more contemporary. I own all Audio Research equipment, and have enjoyed their sound and reliability for decades.

 

jea48
4,266 posts
 

Owners Manual for the VT100 and VT100 MK II.

https://www.arcdb.ws/Database/VT100/ARC_VT100MKII_manual.pdf

Note, page 1:

Diagram indicates relative positions of all (16) tubes on the two circuit boards as viewed from the front and looking down from above the amplifier. 

Next go to page 2:

2) ........ match its location "V' number (written on the base of the tube) to the "V" number printed next to each socket on the circuit board. (see accompanying tube location diagram.) Firmly seat each tube in its matching socket.

Next go to page 4:

Output Tube Bias Adjustment

Note, no mention of the input and driver tubes Bias Adjustments.

Just a guess most of the VT50, VT100, VT100 MK II, and VT 200 amps were damaged by their owners when they bought their own tubes and did a total re-tube of the amp. If the owner only replaced the power tubes there was no problem... Problem was when the 6922 tubes were replaced... Nothing in the owner manual about needing to bias the 6922 tubes. Just the output power tubes needed to be biased... Problem is if the new 6922 tubes Triode sections were not tightly, closely, matched and the new tubes were not biased to ARC specs, (especially the driver tubes), damage to the amp will be the result. and sometimes the damage is extensive.

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