Suggestions please!! --Need to replace vintage Audio Research VT 200 Tube Power Amp
To the OP. Sterophile reviewed what appears to be your speakers, here: stereophile.com/content/proac-response-4-loudspeaker-measurements (I deleted the www prefix in case the link is deleted.) If this is your speaker and you plan on keeping the Proacs, JA noted a couple of points that should be kept in mind. First, the Proacs are not very sensitive. JA measured the Proacs' sensitivity to be 85.5db, which is not high. That would suggest you will need power to get the best results from your speakers. Notably, I checked the ARCDB website and looked up the specs on your VT-200. Your current amp has a rated power output of 200 watts per channel and power supply energy storage of 674 joules, all of which permits the inference that you have a pretty hefty amp. Second, the Proacs' impedance curve is pretty rocky. JA comments that a high output impedance tube amp would add sonic coloration to the speakers' frequency response. The ARCDB website reports that your VT-200 has a low'ish output impedance of less than 1 ohm (damping factor is 11). Although I am a fan of ARC products, if you are trying to keep costs down, you might find that you are biased (pun intended) to look for a quality solid state amp that has a lot of rated power. There are many fine brands on the market and I'll let other members make specific recommendations. That said, if you are inclined to stick with a low'ish impedance tube amp with umppff, in general, and another ARC amp in particular, you may want to consider the Ref 150 SE. If too pricey, maybe a Ref 110 if you see one pop up. I own the Ref 150SE and it drives my speakers like a champ, but then again, my speakers have a rated sensitivity of 92db. I have another suggestion. I think your VT-200 is a pretty good match for your Proacs for the reasons explained above. I appreciate your frustration with frequent repairs, but nobody knows an ARC amp like ARC. Why not call ARC and see if they can go over your amp from top to bottom. I am sure ARC could put your VT-200 back to original spec and augment its reliability factor, … if they still repair the VT-200. You should also ask ARC if your amp can run with KT-120 power tubes. That would make a big difference in SQ. I would also ask if you can have the MK II upgrade done. In any case, I would be hesitant to drive your Proacs with much less power than what you have now in your VT-200. Hope this helps. BIF |
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The B+ voltage on the output tubes is too high for those Russian-made KT-series tubes! This wouldn't be a problem for original USA 6550's or British KT88's. But NOS supplies of those tubes are practically nonexistent! ARC shouldn't run those Russian tubes so hard! This has been a constant problem with ARC tube amps for years! |
All the ARC VT Series Amps are a pain in the butt to bias, and it’s just not the output but input tubes as well that have to be biased. Without extremely close matched tube sets (both) it is nearly impossible to bias these amps. You pretty much have to tear the amp apart to bias them. The cost to re-tube the amp alone isn’t worth it. There’s a good reason you don’t see these amps on the used market anymore; cost to re-tube, bias and most have blown up. You can probably fix it easy enough but it’s just not worth the cost for all new tubes which you’ll need to do or it’s just going to fail again and have a tech that knows this amp well bias it. If ARC will even touch it, the cost will be insane. Lots of great SS amps I’d move to before even thinking about fixing your VT 200. I’d just throw it out there for sale and someone will buy it... hopefully they’ll know what they’re doing. Maybe just sell all three of your ARC pieces and look for a used Gryphon Diablo 300 and just make life a lot easier. |
I can't thank you all enough for taking the time out to send me your advice. Looks like I have many leads to follow up on, and I'm sure I will find a great solution. Part of me would love to rebuild the VT200, it really is a special amp and pairs up nicely with the ProAcs, and that's what drove me to do the last round of repairs, when I had already sank almost $3K on the first repair. The guy who did the repair is the only shop in NYC that AR recommends, so he knows the gear very well, but there's clearly something that's failing in the electronics that he's failed twice to identify, so it may just be that its time has come! Plus the damn thing weighs like 100 pounds so I've needed to get help every time I've had to move it. So I guess it's time to move on, and hopefully it will find a new home with someone who will be able to bring it back to life! Thanks again and will follow the leads you all have generously provided to me, and I'll let you know how it works out. Be safe everyone! |
unless you are playing in a church or auditorium, those speakers, no way do you need that much power, they are 89 spl efficient, and 8 ohms. https://www.stereophile.com/content/proac-response-4-loudspeaker-specifications I would say 75wpc is plenty, perhaps even a bit less. Do you have a friend with a low powered tube set, i.e. 35wpc? just try that, to establish a comfortable minimum, you will be surprised. New or used, just make sure you can return what you try. |
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 |
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. |
What gpgr4blu says makes a lot of sense. What he did not speak about is the difference the SE upgrade made to the stock Ref 150. I owned the Ref 150 and had ARC do the SE upgrade. The SE upgrade is more than just a KT-150 tube drop in. The SE upgrade also entailed numerous part change-outs. I did the KT-150 drop-in into my stock Ref 150 and did a lot of listening. Later, I had the SE upgrade done. Major and very noticeable improvements across the board. Well worth the money. I never heard the Ref 160 so I cannot give you any comments about how the Ref 160 stacks up against the Ref 150SE. If gpgr4blr says that the Ref 160 is about 12 to 13 percent better than the Ref 150 with KT-150 tubes, I surmise that the Ref 150SE may be closer still to the Ref 160. In any case, the Ref 150SE is a terrific amp. Definitely something to consider. BTW, not to throw a spanner into the gears, but at some point you might want to think about upgrading your Ref 2. Perhaps asking ARC if they still do the MK II upgrade. In any case, as far as the front end is concerned, you should call ARC and ask the customer service rep for some suggestions. The late model LS preamps are pretty darn good. BIF |
Congrats!!! Good decision. I wish you many years of listening pleasure. I have some "care and feeding" suggestions. First, as you now know, the amp is heavy: 75 pounds as a stand-alone; 100 pounds when boxed up. Consider ordering a bunch of bias resisters from ARC (2 different resisters per tube). They are cheap. If in the rare case, a KT-150 arcs, you can avoid sending the amp back to ARC for a simple burned resister change-out. Hopefully, you are close to a tech who can do the job, or if you are handy, you can do it yourself. But always remember, … there are high voltage touch points all over the place under the hood. So be very careful when fiddling under the hood. Second, if you don't have a multi-meter with probes, you need to buy one in order to check bias. I check bias every couple of months. The KT-150s will drift over time. And don't get OCD about bias changes. Bias voltage (65 mV DC on the set tube) will change as line voltage changes. Don't go nuts about line voltage changes. Line voltage will change by the hour, especially if home appliances draw heavy amps, e.g., air conditioners, and maybe the washer and dryer. Hopefully, your amp came with a tiny plastic thiga-ma-giggy screw driver to adjust bias. If not, I am sure you can buy one from ARC. Again, … be careful about high voltage. Last point … tubes. ARC charges a fortune for replacement matched KT-150s ($275 per tube). Kevin Deal did a great job on my last re-tube. Bias deltas between the set tube and the slave were within 3 or 4 mVs, which is good. ARC may be a little tighter, but not significantly so. Upscal Audio charges $127 per tube. You need to buy matched pairs, preferably matched quads. I have a question for you. Which taps have you tried and settled on? I have switched back and forth between the 4 and 8 ohm taps many times, but have settled on the 8 ohm taps. FR may be a little tighter on the 4 ohm taps, but for some reason my amp/speaker combo just sounds better off the 8 ohm taps. That said, FR will fluctuate +/- .8 db off the 8 ohm taps (an Ohm's Law thing), so in a sense, the amp is a bit of a tone control. Ignore it. No speaker is 100% flat. And when you consider the room effects, ... that is another tone control. John Atkinson measure the FR of the Ref 150 (not SE) here: stereophile.com/content/audio-research-reference-150-power-amplifier-measurements (www deleted). If you have any questions, feel free to send me a PM. I love the Ref 150SE. It has been a dependable workhorse for many years. BIF P.S. -- If and when you think about a preamp upgrade, you will be shocked by the ARC Ref 6. Amazing!!! |
