Post by Owen Y on Jun 16, 2017 14:48:05 GMT 12
Audio Research announces a special program to US owners of older Audio Research eligible units of amplifiers, preamplifiers, or phono preamplifiers to Trade Up! to current models. The 2017 Trade Up! Program is good June 15 – July 31, 2017.  audioresearch.thehouseofmouse.it/en-us/company/trade-in-to-trade-up-programWow, some models eligible goimg back to 1970! Including my old D70 MkII power amp.
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Post by guitardude on Jun 16, 2017 15:05:14 GMT 12
The D70ii was a classic power amp though Owen. Still got it ?
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Post by Owen Y on Jun 17, 2017 10:56:02 GMT 12
No - it went to Dave Whittaker as part-payment for building an Aura TT for me! (Dave had Magnepans at the time & had been reading Martin Colloms' partnering of MG IIIs with ARC  ) ARC always had innovative design, not just following old-school tradition. And of course, build quality was solid.
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Post by michaelw on Jun 17, 2017 14:02:26 GMT 12
looking through the list they don't want any early solid state units back
hahaha
also forget about trading your vsi integrated or even an sp6 preamp
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Post by Owen Y on Jun 17, 2017 15:39:05 GMT 12
Interesting, I thought that some later versions of SP6 were considered 'collectable' in some circles. SP8 yes - but no mention of SP8 MkII.
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Post by colinf on Jun 18, 2017 8:47:49 GMT 12
I visited the Audio Research factory in Minneapolis in the early 90s when William Z Johnson was the designer. I was amazed they still keep spares for all the old Audio Researches including faceplates and transformers. I wonder if they are running out of these old parts and want to maintain an inventory of them.
AMR-iFi R&D
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Post by colinf on Jun 18, 2017 8:58:05 GMT 12
Audio Research partnered their amps with Magneplanars in the factory too. They were in Minneapolis and Magnepan were on the other side of town in White Bear Lake, north of Minneapolis. AR used lots of different speakers to test their amps on including Proac Response 3s when I visited.
AMR-iFi R&D
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Post by guitardude on Jun 19, 2017 14:33:41 GMT 12
Would still happily own an early ARC pre or Power amp. I remember Dave having an SP6b I think it was, not sure if he had his D70ii at the same time I had mine. (What ever happened to all of Daves gear after he died BTW ? I think he had Beveridge speakers at one point, last time I spoke to him he was building Tannoy horns).
Nice to see a company supporting all their legacy gear though.
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Post by michaelw on Jun 19, 2017 16:08:05 GMT 12
funny thing about the arc/magnepan relationship was it appeared largely one-sided
magnepan was fond of voicing their speakers with more mundane amplifiers and receivers.
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Post by Owen Y on Jun 19, 2017 17:30:56 GMT 12
(What ever happened to all of Daves gear after he died BTW ? I think he had Beveridge speakers at one point, last time I spoke to him he was building Tannoy horns). Dave's stuff went to many good homes - most of it I hope anyway. The Beveridge electrostatics had a problem in their in-built tube amps, never got resolved AFAIK. Tannoy GRF Autograph horns - 2 (or was it 3?) pairs were made. (Dave's son, Simon, is a member of this forum.)
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Post by colinf on Jun 19, 2017 18:14:58 GMT 12
If you want to know all about Beveridge electrostatics, talk to my friend Roger Modjeski in Santa Barbara. He worked for Beveridge before he went out on his own with his company Music Reference and RAM selected tubes. (Tubeaudiostore.com) He helped design the tube electronics for it AFAIK.
AMR-iFi R&D
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Post by michaelw on Jun 19, 2017 18:51:55 GMT 12
music reference
denco imported them in the 90s.
the preamp and head amp were so-so
the rm9 tube power amp was really nice.
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Post by Owen Y on Jun 19, 2017 20:23:46 GMT 12
Also a Pre-preamp, as I recall playing with once - 6DJ8s of course.
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Post by michaelw on Jun 19, 2017 20:55:28 GMT 12
head amp = pre-preamp 
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Post by colinf on Jun 20, 2017 8:54:16 GMT 12
RM-9, a classic Roger Modjeski amplifier. I think he discontinued it because of the variability of the quality of 6dj8s available then. But there are enough good modern ones around that I think he cut its production off prematurely. The RM-200 uses a SS hybrid input stage which is quieter and not prone to drift. The RM-9 relied upon the characteristics of the input 6dj8 for its proper operation and not many owners realized this. It needed to be periodically readjusted by the owner. I couldn't imagine my father doing this on his RM-9. Speaking about adjusting input stages, Audio Researches needed to have them adjusted too; usually by a service tech, as the voltages exposed with the lid off were dangerous. At least Roger made the adjustment available on the top panel of his amp without needing to expose high voltages. Roger's pre-preamp was highly susceptible to having proper 6dj8s with noise, microphonics, and characteristics making it a daunting ownership experience. Audio Research went to jfets and mosfets in their hybrid designs for these reasons.
AMR-iFi R&D
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Post by Owen Y on Jun 20, 2017 10:27:05 GMT 12
You will recall that Roger started selling RAM tubes - tested, low noise, Yugo 6DJ8s of course, mostly ARC - the D70 MkII (& D115) had output tube bias pots on the pcb & the 6550s were quite closely packed & hot. I used to run mine with the tube-cage off (unwisely) & I will always remember the 'BANG' when a small screwdriver rolled off a shelf above onto the pcb - fortunately as it turned out, the 400vdc HT track instantly vaporised & saved the amp from any major damage
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Post by michaelw on Jun 20, 2017 10:46:24 GMT 12
in most cases 6dj8's were a pain in the ass but maybe it was the implementation ?
my counterpoint sa7 (and other cp models) had endless problems with them, two were used in the line stage.
even ram replacements were duff.
the official fix was to ditch them altogether and substitute a ss line stage.
eventually the followup x000 series went the same hybrid route.
much more reliable compared to the first gen but the cost was a chunk of musicality.
my arc sp8/2 also used 6dj8s and that preamp was faultless in the many years i used it.
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Post by colinf on Jun 20, 2017 11:47:56 GMT 12
Yes, and they made it a lot easier to maintain these amps. I used to service the D70 and 115 amps, and others as Trevor was the Audio Research agent at the time in Melbourne. It was always fun to adjust the bias, as you can attest! Especially the D115 with its cathode resistors right next to and underneath those hot tubes. I got it down to a fine art. I would hold the multimeter probes in place with two fingers. Clips on the multimeter leads wouldn't work as the probe would invariably settle on the side of a hot tube and melt the plastic, creating a horrible smell and a mark on the tube glass. So I held them with two fingers and blew a gentle breeze over them to stop my skin burning next to the tubes, while I adjusted the relevant bias pot with the other hand. One of our customers saw me do this one day and decided to try it at home. But he couldn't hold the leads with his fingers properly so he held them with his mouth. I couldn't do that because the heat would have been extreme, but he did. One day he was concentrating on reading the meter and adjusting the bias pot when a loud crack and an explosion happened right in front of his face. He was shocked and partly blinded by the flash. After he calmed down he remembered what had happened. In his effort to hold the meter probes in place with his mouth he dribbled down a probe right onto the exposed 430volt anode track, and oozed over onto the adjacent heater supply causing a short circuit. He got me to bias his amp from then on.
AMR-iFi R&D
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Post by colinf on Jun 20, 2017 12:09:35 GMT 12
Those circuits that used 6dj8s were very ambitious designs that I suspect the designers wanted to showcase the high performance possible from these tubes. But the reality is slightly different. They were designed as RF tubes for tv receivers and tuners. They suffered from heater to cathode leakage, and also because the frame grid wires were so small and in such proximity to the cathode they were prone to microphonics at audio frequencies, something that isn't a problem at RF operation. Linearity was also a problem at low current. Higher current made them go noisy faster. Ditto 6gk5, 6c45pi and 6h30. When I designed my first hybrid amp I used 6dj8s on the input and driver, only to have them fail gradually over the next few months from heater to cathode problems. So I replaced them with other, audio tested tubes such as 6072 and 12au7, with good heater insulation. It's been flawless ever since. I'll only use a 6dj8 now in a circuit that is self-adjusting. The SP8 used 6dj8s in the cathode follower position so the characteristics weren't critical, but their low output impedance was an advantage.
AMR-iFi R&D
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Post by Owen Y on Jun 20, 2017 13:23:37 GMT 12
Yes, the Counterpoint SA7 was a simple, no-frills design - partly a reason for it's 'direct', transparent sound, but would not have incorporated such good EE design practice as 'elevating' heater voltage to minimise cath-heater potential & noise leakage that colinf mentions, esp in these ultra-tight tolerance 'frame-grid' toobs. (This much I've learnt from hassles as described above ) PS. I should mention that, when biasing the D70, I used a handy skinny plastic trimpot screwdriver - & somehow I think I managed to use meter hook probes! (That screwdriver accident was simply foolishness!)
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Post by Owen Y on Jun 21, 2017 15:48:52 GMT 12
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