Fixing chaps’ amplifiers today

Posted on 16 February, 2010 by | 6 Comments

David Davis

I’ll put up a shot later, of one I fixed earlier.

Here it is:-

Great amp, underdesigned power supply and fusing, needs soft-start

Wish it was for ready money….

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6 Responses to Fixing chaps’ amplifiers today

  1. chris southern | 16 February, 2010 at 1:29 pm |

    If you could make guitar valve ampheads with the soft crunch made popular by many american artists over the years you could make some nice money from that.

    I’m a mesa boogie man myself, you just can’t beat a good valve amp :)

  2. David Davis | 16 February, 2010 at 2:01 pm |

    I can make you one of those, Chris, no worries.

    I favour the old US 6L6 varieties, or the newer Soviet 5881′s which are very bright and sharp, above most types. The KT88 is too squashy, the EL34 sounds like an EL34, the EL84s are not strong enough, and it’s hard to match 807s although they are the best.

  3. chris southern | 16 February, 2010 at 2:35 pm |

    I wish i had the money David (it took years to save up for my dual rectifier) otherwise i would take you up on the offer.

    Custom valve amps are in demand, it may be a nice possible earner for you.

  4. Chris Morriss | 16 February, 2010 at 7:30 pm |

    It’s not the bottles that are the problem, but getting decent OPTs. Those shiny black Chinese metal shields usually contain lots of air, and a pretty poor quality transformer. Have a look at the Sowter site to see just how much good quality OPTs cost these days.

  5. David Davis | 16 February, 2010 at 8:18 pm |

    On the “Steel Beast” (see posts about it on this blog)
    I actually _/designed/_ the output transformers myself, for 4xKT88 in two pairs, class AB, for alternate pentode or triode-connection, with ultralinear taps at 43%, 50% and 59%, all switchable while live. They ended up costing £520 each, but I was not paying thankfully.

    The primary inductance for each one was 688 Henries. Each transfr weighed 15.5 Kg (about 35lb.) The customer wanted the secondary output wndings to be silver bullion but I dissuaded him, they were expensive enough already.

  6. David Davis | 16 February, 2010 at 8:19 pm |

    I will tell you who my transformer people are, but then I would have to kill you.

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