Suggestions please!! --Need to replace vintage Audio Research VT 200 Tube Power Amp

Charles1dad is correct.  JA measured the Proacs sensitivity to be 85.5db.  JA wrote: "The speaker's sensitivity on the HF axis (measured using B-weighted noise) was somewhat lower than specified, at 85.5dB/W/m vs 89dB/W/m."  In my opinion, I would err on the side of more power, … not less. 

And Adg101 makes an excellent point about "care and feeding" of the VT-200.  If true, it appears that the VT-200 is a pain in the butt to bias.  I surmise that blown bias resisters may be a major operation to replace if a power tube arcs, … and arcing power tubes just go with the territory.

The innards of my Ref 150SE are wide open.  So if a bias resister blows, I don't need a neurosurgeon to replace it.  And I check the bias on my power tubes once a month, ... an easy job.  Bias drifts and that is also part of the care and feeding that goes with older ARC amps.  That said, I understand that new ARC Ref 140 is self-biasing and has a resettable circuit breaker if a KT-150 arcs.  Very nice but very expensive.   

I am sure you will make a good and practical decision.  I don't know your budget, and that should have been the first question, but if you like ARC tube amps and have the budget, give a thought to the Ref 150SE.  It has (I) a very robust power supply (1040 joules), (ii) can easily push out 150 watts into an 8 ohm load off the 8 ohm taps, and (iii) has a relatively low output impedance for a tube amp (approx. 6 ohms  off the 8 amp taps and even lower off the 4 ohm taps).  

Good luck and stay safe.

BIF

Ooops typo:   … (iii) has a relatively low output impedance for a tube amp (approximately, **.6** ohms (i.e., less than 1 ohm; damping factor is 14) off the 8 amp taps and even lower off the 4 ohm taps).  

Hi BIF,
Thank you again for your advice.  I have managed to locate a brand new ARC Ref 150SE at a deep discount ($9,000) and within my budget (apparently it has been discontinued?) and I am seriously considering purchasing it.  My only hesitation is whether 150 watts per channel is adequate to power my ProAc Reference Fours?  I know you recommended I give this amp a thought, so I was wondering if you might have some additional opinion on this amp, now that I've zero'd in on it? Thanks in advance!!

Mike

Karmicg … as far as I know, the Ref 150SE is still in the ARC lineup.  See here: audioresearch.com/product/reference-150-se/ (www prefix left off)

You raise a good question about muscle power.  The VT-200 is rated at 200 watts/per channel.  The Ref 150SE is rated at 150/per channel.  I really do not know if 50 watts is all that significant since the relationship between power and loudness is logarithmic.  In other words, 25% less power may not result in a 25% decrease in loudness.  Perhaps some of our techie members can offer an opinion.  

Here is an interesting factoid.  The VT-200 has a 674 joule energy storage power supply as compared to the Ref 150SE, which has a 1040 joule storage power supply.  See the ARCDB web site here: arcdb.ws/model/VT200.  (www prefix left off)  Just toggle to the Ref 150SE to compare.

What this means is that the VT-200's power supply can muster 674 watts/per second if a music transient is sent through the amp.  By comparison, the Ref 150SE's power supply can produce 1040 watts/per second in a pinch, … almost 50% more uuummpph.   That's a lot of back-up reserve for an amp that is rated 50 watts lighter.

I wish I could tell you with absolute certainty that the Ref 150SE will produce all the power you need, … I can't,... because I just do not know.  But I can tell you that the Ref 150SE is probably a much better sounding amp than the VT-200.  And the robust power supply might be able to carry you through.  

IMO, the Ref 150SE is a super sounding amp.  I love it.  And so far, it has not given me any headaches.  I never heard the VT-200. I surmise that the Ref 150SE sounds better because it is a current generation amp and there has been a lot of water over the dam in terms of technology, design and parts since the VT-200 was first issued.

Here's another plus:  the Ref 150SE uses KT-150 tubes.  These tubes are really something else.  IMO, much better sounding than 6550s.  A word of warning though.  KT-150 tubes are expensive and must be tightly matched.  ARC charges $275 per tube.  But here's some good news.  Upscale Audio does a really good job of super matching KT-150s for ARC amps and charges $128 per tube.  I just bought 2 quads of KT-150s from Upscale and was pleasantly surprised.  I realize that a retube could still cost some change, but the KT-150s last 3000 hours. 

And here is another most important fact:  you can easily change out the tubes and adjust bias without electrocuting yourself.  :)  That is a big improvement over the VT-200, based on the comments above.  Another word of warning.  Although I have been very lucky with bias resisters, they do blow on rare occasion.  Hopefully, you have a local tech who can switch out a blown resister, ... and even better in your home.  The amp weighs 75+ pounds.  If you go with the Ref 150SE, preorder some replacement resisters from ARC.  They are cheap.

Hopefully, my comments are helpful.  I am sure other members will weigh in too. 

Good luck and happy shopping.

BIF

I have owned a Ref 110 and Ref 150. I then placed KT-150s in my Ref 150 which brought it very close to the performance of the Ref 150SE.
The Ref 110 drove Watt Puppy7s and then Sashas. The Ref150 drove Sashas and then Alexia 2s. I test listened in my home Ref 250 monos v the Ref 150 with the Sashas and there was hardly a difference in the power department--virtually unnoticeable to me.
 I now own the Ref 160 monos with Alexia 2s. My take is that the Ref 150 has more than enough power (check out the big power supply) to drive ProAc Response 4s. Although the Ref 160 monos are the best ARC amps I have ever heard, you pay a lot for the extra clarity, power and imaging. Maybe an overall 12-13 percent difference over the Ref 150 with KT150s. IMHO, the Ref 150 with KT150s or the Ref 150SE are the best bang for the buck by far in the ARC line and indeed I cannot say enough about what a blazing bargain they are in the larger amplifier market.
Get a Ref 150 or Ref 150SE. DO NOT get a Ref 110. The difference between the Ref 110 and Ref 150 were substantial. The Ref 150 sounded more powerful and made the Ref 110 sound wispy in comparison. Hope this helps.