OK, but the D70 II is now a 25 year old amp, the D-76 even older. I'd say they've proven their worth. The bias procedure in the D70 II is absurd, but it will hold the correct setting for years. This is a pretty reliable amp. I've had mine for a long time, changed tubes infrequently, and never really had any problems. (Hopefully I didn't jinx myself with that last claim!)
What Audio Research power amps have you owned or admired?
- Thread starter Jay_S
- Start date
There was a very simple "non-official" way of checking bias in the D70 and several other Audio Research units. These amplifiers were partially cathode coupled and the 4 ohm tap was grounded, the "0" and "16" ohms being symmetrical. After the amplifier was once properly biased using the test points I took note of the voltages measured between ground (4 ohm tap) and the "0" and "16". At any time I could easily check or adjust the bias in thirty seconds. As the resistance of the transformer coils was low a voltmeter with a .1mV sensitivity should be used.
Jay-I don't buy the statement that the bias will hold the correct setting for years. The bias changes as the output tubes age. Usually 2 years is about all you get out of a set of output tubes unless you never turn your system on. So to think that your output tubes aren't going to change over a 2 year period and not require re-biasing is stretching things a bit. It's not a function of the bias circuit being stable and drifting. As the tubes age, they will change the bias.
Actually Mark I knew a neighbor who had a D76 and had never changed any of the tubes in the amp since he bought them 10 years or more ago
Guy bought a SOTA system (obviously composed of TAS recommended gear bought from Lyric) at the time (Linn/VDH tipped cartridge/AT arm, SP3A-1VA, Timpani 1Cs) and was told that the quality of tubes had gone down so never change the tubes. He also didn't believe in cables and b the time I knew him, the ends of the zip cord between the amps and speakers had turned green and black. Needless to say, it was one of the harshest and brightest systems I've ever heard. But my neighbor was happy. He didn't get what I heard with my then cj Prem 4/3, modded MG3as and MIT cables.Also knew a guy who was at that time Dean of a Dental School who quite possibly had one of the worlds worst sounding systems money could buy. Dick Sequerra had built him these triamped (Sequerra modded hafler DH500s) speakers that were totally discontinuous sounding, a Berning TF-10 (hadn't changed the tubes since he bought it 10 years ago-though Berning always claimed he unit was gentle on tubes) and THE original VPI table. His room made a real case for room acoustics as it had a tile floor and all hard solid reflective walls and ceiling. The speakers were behind a curtain (that was there playing or not) because his wife didn't like the speakers. Brought over the Merc Hi Fi ala Espanola and his comment was great music, too bad it was recorded badly. Didn't have the heart to tell him it wasn't the LP, it was his system. Nothing would have sounded good in that room.
By "years" I didn't mean more than a couple. I stand by my statement and my system does not resemble the dysfunctional setups of Myles' acquaintances. Here are the facts: I change output tubes every four years and check bias every two years. Because the procedure is such a pain I am meticulous in checking the settings. The bias does indeed hold very well over two years but I double-check everything just to make sure. I do make some adjustments but they are really small. My usage of the ARC is moderate, probably 1,000 hours per year, about 20 hours per week. You can't really generalize about how long output tubes last - usage varies and some amps are really rough on output tubes.
I don't really think that changing tubes every two years or so is such a big deal. Same for having the bias adjusted by a tech. I do agree that it would be nice if the amp had a self-biasing circuit or was easier to bias.
Nonetheless, I am still very impressed with this amp; I have heard the Classic series and the VT 100's and I have also heard the Quicksilvers. IMHO none of them is better than the D70. One of the strange aspects about
this hobby is that most listeners and reviewers assume that since a product is newer than yesterdays model, it stands to reason that the new model is automatically superior. I know several 'philes who wish that they hadn't sold their
old equipment that made beautiful music to get the latest and greatest, only to be left wandering what happened to their sound. IMHO, the D series of ARC amps and the D70,D115 and maybe the D250 along with the
M100's are the true sweet spot of the ARC amp line in the last 25+ years.
Nonetheless, I am still very impressed with this amp; I have heard the Classic series and the VT 100's and I have also heard the Quicksilvers. IMHO none of them is better than the D70. One of the strange aspects about
this hobby is that most listeners and reviewers assume that since a product is newer than yesterdays model, it stands to reason that the new model is automatically superior. I know several 'philes who wish that they hadn't sold their
old equipment that made beautiful music to get the latest and greatest, only to be left wandering what happened to their sound. IMHO, the D series of ARC amps and the D70,D115 and maybe the D250 along with the
M100's are the true sweet spot of the ARC amp line in the last 25+ years.
I have to tell you a story about the SP8. A good friend had his SP8 on a equipment stand with a lamp situated maybe 2-4 ft over the unit (at the time, think he was also using the D250s). For some reason, if you waved your hand between the lamp and SP8, one heard a hum in the system
May be optical voodoo. The muting of the SP8 used an optocoupler in series - if there is a light leak in the optocoupler the device will become sensitive to the mains lighting flicker that can induce hum!
Both the SP10 and the SP8 used this component, that some times needed replacement after a signal tube broke.
Wow that makes some sense and that would explain the mystery that has existed for about 20 years
Davey-I am in the opposite camp that thinks that everything new is better. I believe the MS-190 is older than the D-70 MKII. The MS-190 was a much bigger sounding amp than the D-70 and more the life-like to my ears. I recently bought a McIntosh C-2300 in hopes of replacing my Counterpoint SA-5.1 but it wasn't close and the Mac went back. And Davey, did you really hear the MS-190 which are/were extremely rare or just another Quicksilver amp?
Myles-I bought my D-76 from a guy who said it was broke because the sound was distorted. I paid him $300 and took it home. I pulled out my trusty Fluke 77 and checked the bias and it was way off. I reset the bias and the amp sang. I used to check the bias about once per month and it always needed some tweaking. I can't imagine checking the bias once every 2 years. And the tubes it came with were GE 6550 tubes. I loved the ARC D-76 for many years. There are some output tubes that seem to last forever like real GEC KT-88s and real WE 300Bs. Most common output tubes don't share that type of life and bias should be checked on a regular basis as it will change as the tubes age-unless you never turn it on. If you think otherwise, your sound will gradually deteriorate.
Jay-IMO, 20 hours per week is a fair amount of listening. What amp do you have and what output tubes are you using? If you tell me that you can get away without checking the bias for 2 years and when you do it has hardly changed, hats off to you. That has never been my experience in owning tube amps for more years than I care to count.
Steve Williams
Site Founder, Site Owner, Administrator
Its interesting Mark
When I had my Lamm ML2.1 i found that I was rebiasing the left channel almost every time I turned on the system. It didnt resolve with retubing or checking the AC outlet Not sure why.
Since i have had the ML3s i check the bias every time and it is rock solid and never had to rebias.
When I had my Lamm ML2.1 i found that I was rebiasing the left channel almost every time I turned on the system. It didnt resolve with retubing or checking the AC outlet Not sure why.
Since i have had the ML3s i check the bias every time and it is rock solid and never had to rebias.
You are quite correct -- the 20 hours was my math mistake, and doesn't represent a good estimate. Upon reflection, my hours are moderate but not quite that high. (OT - be careful of estimated hours specified by sellers of used phono cartridges!) I use an ARC D70 II with external cooling fans. Sometimes I swap the amp out for a solid state amp in the summer. Original power tubes were Philips 6550, then ARC, and then Svetlana 6550Cs.
I bought it used some years ago (ca. 1996?) with all new tubes. Length of ownership is not a great metric as this amp has been packed away a couple of times. This fall it will be time for the next set of 6550s and I am considering sending it off to ARC for more complete maintenance.
mep, I bought my D70 mk2 about two months ago from the original owner. Amazingly, he hadn't replaced the tubes since new!! In addition he had bought the amp as an original D70 in '83 and sent it in to have it updated to mk 2 status the next year. The driver tubes were still meeting spec, the power tubes were shot.
My tech reminded me of something interesting; the prior owner thought the caps should be replaced due to their age, BUT in fact the caps are very easy to check and have a MUCH longer life than most a'philes realize, mine were all fine. My tech, who is very well known in the Mac circles, ( and is one of the few auth Mac tech's on the westcoast) says that he rarely sees caps that truly need replacement, most of the manufacturers replace them prior to them needing to be replaced as that is where the money is! Nonetheless, I did a complete re-tube, BUT I could have left the driver tubes alone, even though they are now nearly 27 years old.
My tech reminded me of something interesting; the prior owner thought the caps should be replaced due to their age, BUT in fact the caps are very easy to check and have a MUCH longer life than most a'philes realize, mine were all fine. My tech, who is very well known in the Mac circles, ( and is one of the few auth Mac tech's on the westcoast) says that he rarely sees caps that truly need replacement, most of the manufacturers replace them prior to them needing to be replaced as that is where the money is! Nonetheless, I did a complete re-tube, BUT I could have left the driver tubes alone, even though they are now nearly 27 years old.
D-70, D-79 (mine, currently non-functional, sob), D-90, a couple of their early solid-state efforts, and a couple of the later tube and SS ones (can't remember them all).
Davey-most electrolytic caps are rated for 20 years. In order to check them correctly, they need to be electrically isolated from the circuit by disconnecting them and hooking them up to a good capacitance checker that will check to see if it meets it specified value under voltage and check for leakage. Big caps can go bad suddenly with a big bang. Sometimes you don't get a warning like a buldge on one end that tells you something nasty is about to happen. Some caps won't meet their specified value anymore. Once your main power supply caps are over 20 years old, you have to ask whether you want to be safe or maybe sorry. Everything works until it breaks. Some things just break harder than others.
^^^ What he said, especially for HV (high-voltage) caps. One issue is that a capacitance checker is rarely good enough; it will record a drop in value, but it takes a good one to assess the shunt leakage and series resistance that indicates a real problem, and even that may not show how it works under load in the circuit. When I was working on this stuff I had a test bench with a few jigs for testing capacitors.
By the time you hear hum in the output, the caps are usually really bad and on the edge of catastrophic failure.
The lifetime of caps, and tubes, is dependent on many things, among them heat, vibration, bias levels and ripple in the supply, etc.
By the time you hear hum in the output, the caps are usually really bad and on the edge of catastrophic failure.
The lifetime of caps, and tubes, is dependent on many things, among them heat, vibration, bias levels and ripple in the supply, etc.
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