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