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Thread: What would you never buy again? What would you like to own again?

  1. #81
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 268
    I'm Dennis.

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    I tend to agree Steven on valves, having built numerous amps with them, they look nice, comforting, have poorer specs., are inefficient, and need maintenance.

    Used my Nelson Jones class A 10+10 for about 5 years and one channel went dead.
    Borrowed a friend's Lowther amp, and the bass was uncontrolled, woolly.
    Then bought a 303 and the bass in that was also woolly, so I sold it to a BBC engineer.
    It turned out that there was a manufactured faulty BC107 that had failed in my own amp, replaced, done.

  2. #82
    Join Date: Jan 2009

    Location: Essex

    Posts: 15,643
    I'm openingabottleofwine.

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    Quote Originally Posted by Arkless Electronics View Post
    That's lostroh..... Sorry to be pedantic. IIRC it was pure class A, certainly to 25W. Also IIRC it had an input impedance of only something like 1K!! Definitely no good with a passive

    Edit: This is very IIRC... but the Pioneer M90 I believe used very similar circuitry... just not in class A.
    Correct concerning the orthography, incorrect concerning the pure Class A. The Lostroh and Otala design is Class A up to 3W (into a 4 Ohm load), and does as you say have an usually low input impedance: 3.4 kOhm.

    I built one in the '80s using 2N3055s for the output transistors and drove it successfully with a Quad 44 preamp, the whole powering Quad 57 ESLs.
    Sounded wonderful, but did run hot despite using a massive heatsink. Maybe one day I might re-build it as a pair of monoblocks, but since I now use a pair of Levinson ML-2s this doesn't have a high priority.
    Have you listened to this month's choice in the Album Club?

    Barry

  3. #83
    Join Date: Jan 2009

    Location: Essex

    Posts: 15,643
    I'm openingabottleofwine.

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    Quote Originally Posted by Pharos View Post
    I tend to agree Steven on valves, having built numerous amps with them, they look nice, comforting, have poorer specs., are inefficient, and need maintenance.

    Used my Nelson Jones class A 10+10 for about 5 years and one channel went dead.
    Borrowed a friend's Lowther amp, and the bass was uncontrolled, woolly.
    Then bought a 303 and the bass in that was also woolly, so I sold it to a BBC engineer.
    It turned out that there was a manufactured faulty BC107 that had failed in my own amp, replaced, done.
    My experience is the opposite of yours: I built several valve power amps (based on the Mullard designs), as well as the Nelson-Jones 10W Class A design published in Wireless World.

    I quickly learnt that it was essential to use the best output transformers available, which then were those made by Parmeko, Partridge or Gardeners. But they were reliable, versatile and sounded good. I still have a Radford STA15 Mk, III, which IMO represents the final refinement of the Mullard 5-20 circuit.

    My Nelson-Jones, ran hot, was unreliable and was never happy driving Quad 57s. I gave it away and replaced it with the power section of the Sugden A21 (I knew someone who knew Jim Sugden, so was able to get the PCBs and mains transformer at cost), and later the Lohsroh and Otala design.
    Have you listened to this month's choice in the Album Club?

    Barry

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