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The MV75A had an Achilles' Heel

107.142.146.197

In Reply to: RE: Independently from you, my experience was similar posted by Mick Wolfe on January 06, 2025 at 09:40:08

One of my mentors who was an audio reviewer lent me one to compare with my Threshold Stasis 3 in the early 80s. The C-J reminded me of the AR AU integrated (my first "serious amp" at age 15) in that it sounded great at high output but resolution fell apart at low levels - completely unlike the Threshold.

That was a great learning experience and why I didn't keep the AR amp very long. The Dynaco PAS-3X that followed a year later taught me another valuable lesson about impedance matching. With the preamp's highish 1k ohm output, you needed high input Z amplification. Like the Stereo 120 amp used with it having a 100k value. Forget using many other SS amps like the Crown D150 used the next year having one fourth that value driving double Advents - albeit with an H-K Citation 11 that had no problem.

Gain and impedance matching are both important considerations for ideal partners.

Follow Ups:

RE: The MV75A had an Achilles' Heel - DustyC 06:54:48 01/09/25 (5)
It eats 6550's like a moviegoer eats popcorn. Even GE's only lasted about a year.
- CJ ignored the tube manual - garymuffley 12:29:27 01/09/25 (2)
  The MV 75 had 590 vdc on the plates and if you used the LED bias, the idle current was 75 ma, which equals a dissapation of 44.25 watts of heat! The max rating for the 6550 is 35 watts for the plate. Is it any wonder tubes did not last or fail completely?
  
  The solution was to change the cathode resistor from 20 ohms to 28 ohms and you can use the LED bias and not over dissapate the tube rating.
  - "Is it any wonder tubes did not last or fail completely?" - AbeCollins 12:21:54 01/11/25 (1)
    "Is it any wonder tubes did not last or fail completely?"
    
    The company was formed by two economists and I suspect they didn't bring an actual engineer onboard til much later - but I'm just speculating.
    - RE: "Is it any wonder tubes did not last or fail completely?" - DustyC 19:21:14 01/14/25 (0)
      Bill Thallman was employee number 3 and got the products going. Founded Music Technology after his stint with C-J. He was the go-to guy for updates on their early units.
- Didn't know that - E-Stat 07:05:38 01/09/25 (1)
  While my VTLs run SED 6550Cs reasonably hard with 550V rails, I found a schematic for the MV75 and found it runs them at 590V!
  - RE: Didn't know that - DustyC 08:30:57 01/09/25 (0)
    My pair varied from 600V to 615V. Looked pretty cool when they red-plated!

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