Tubes Asylum

ARC D 70 II

71.63.69.67

dgaapc7

I am getting my second D70, regretting selling one a few years ago.
Question- there are 4 power tubes, either 6550s or KT 88s. There is a fifth power tube that I think is part of the power supply. Can one use an 88 for power supply and 6550 s for power, or vice versa?
Supposed to arrive today. A terrific amp. Will compare to my MC 275 vi and restored MAC 1500, amp section only. Hey, a classic shoot out in me own home.
LowIQ

Follow Ups:

I have an early Dual 50 - www.records 17:52:33 08/14/24 (5)
that is marked Electronic Industries and need a complete rebuild. I got it in a storage clean out of vintage audio stuff almost 20 years ago.
- Dates back to '69 - E-Stat 08:00:17 08/15/24 (3)
  according to ARCDB.
  
  Schematics and pics found at link.
  - RE: Dates back to '69 - www.records 07:39:48 08/16/24 (0)
    I have seen that site. I have no plans for doing anything with it. It make an excellent door stop. :)
    It's in pretty rough shape, especially after digging it out of the tornado rubble.
  - RE: Dates back to '69 - Sondek 09:25:34 08/15/24 (1)
    And I thought my Acoustat amps were ugly. That's a close runner-up to them, IMO.
    - RE: Dates back to '69 - www.records 07:44:32 08/16/24 (0)
      Yeah, she is like a 400 lb woman with 2 kids. You would have to think they were twins, because who could imagine someone sleeping with her twice.
- RE: I have an early Dual 50 - hahax@verizon.net 20:52:41 08/14/24 (0)
  That is old. It was in a period Bill Johnson had sold ARC before buying it back.
  
  It brings back memories. I owned a Dual D MK2 that was modified to a DUAL 50 F MK2. Unfortunately it blew up 3 times in 3 years. That was a difficult version, so Bad Audio Research them selves took my amp in trade for a Dual 51. That was a much better experience.
FWIW dept.: that amp is old enough that the power supply is at risk. - Ralph 09:50:54 08/14/24 (0)
Make sure the filter caps in the power supply have been replaced. You might have already done that, but if not, they have a way of burning up the main power transformer which is something you really want to avoid!
RE: ARC D 70 II - Yes - Chip647 10:00:58 08/08/24 (2)
The "5th" tube is just a pass element for the regulator section.
It just has to be a properly functioning tube of the 6550/KT88 family.
It does not have to match the others.
- RE: ARC D 70 II - Yes - dgaapc7 13:38:24 08/08/24 (1)
  Thanks for the info. I'm listening to it right now, delivered two hours ago. Just biased with 6550's. The 6550s are labeled made in USA, but I can't seem to find a brand label.
  Why did I ever sell the first one I had? The amp is terrific, with the trademark ARC way of making the music sound lively, full, and colorful.
  LowIQ
  - RE: ARC D 70 II - Yes - Akolegov88 02:12:52 08/14/24 (0)
    If the 6550 tubes are straight-bottle shape, they are most probably GE.

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