Recent content by Gary Kaufman

  1. Gary Kaufman

    want to replace st-70

    Time delays on the B+ work better in systems with separate filament transformers where you can delay the primary side of the B+ circuit. I'm sure the relay being used in most of the available delay boards isn't rated anywhere close to 435vdc. The GZ34 already provides a nice slow warm-up, and...
  2. Gary Kaufman

    want to replace st-70

    Sorry to disagree, but <argh> on the Dynaco ST120. I have serious PTSD from that amp. It would be a huge step down from the ST70. I replaced the output transistors a half dozen times in college. Someone tripping on a speaker wire would short the output and POOF. The good news is that the...
  3. Gary Kaufman

    Eico ST40 GW Find - Where do I start?

    I'm guessing it's someone's chem lab results, and probably just got tucked into the ST40 manual :)
  4. Gary Kaufman

    Dynaco ST-70: Base Line Testing

    Dave - Great series of postings, very enjoyable. I have always maintained that most folks have never heard a stock ST70 in good shape. Sure the "mods" sound better - take out a 45 year old board with leaky caps and out of tolerance resistors, charred phenolic PCB and wax dripping - put...
  5. Gary Kaufman

    Solid State Power Supply help needed...

    All good comments - but remember that as you reduce the input capacitor the power supply will act like a choke loaded supply. Most common chokes will buzz like a chainsaw used this way. I don't know who has convinced you of the virtues of a solid state supply, but your schematic is a...
  6. Gary Kaufman

    117 VAC to 5 volt Transformer - Available?

    Tom - If the amp already uses 3DG4's I'd use them. They are similar to the 5U4GB, very well made and easy to source. If you do have 6V filament wiring you could also use a pair of damper diodes, 6V damper diodes are likewise dirt cheap - although most require compactron sockets and need a...
  7. Gary Kaufman

    117 VAC to 5 volt Transformer - Available?

    Hammond 166MS (open frame, ~$17) or 167M5 (enclosed, ~$26) are both 5VCT/3A transformers and available from many vendors including www.angela.com Alternately why not use a 3v rectifier? The 3DG4 is dirt (like $3) cheap and very cool! - Gary
  8. Gary Kaufman

    New filter cap in my FM3

    Remember that measuring caps on a hand-held digital meter is worthless (unless you care about the performance of the cap at 9vdc). Any leakage will make most caps measure high. If you do much repair work an ESR meter is very helpful in evaluating caps in circuit. You also want a meter that...
  9. Gary Kaufman

    5U4GB or 5AR4 in Dynaco ST-70

    I've known folks who ran GZ37's for years - with a 2.8A filament. I'd personally not be concerned about the transformer with a 5U4GB. I would consider adding a Termistor (CL-80 or similar) to soften the start up surge. Lots of Dynaco Docs at www.the-planet.org/Dynaco.html - Gary
  10. Gary Kaufman

    Tube rolling the 6BQ5?

    You need to change your handle, and darn quickly. You don't want to draw attention to the very neat 6DZ7. It's still relatively unknown (as is the 6GK6 which you've also discovered...) I learned about the 6DZ7 in a GE "Ham News" about 15 years ago and have been squirreling them away ever...
  11. Gary Kaufman

    Very Pleased with 1626 SET 'Darling' Amp

    Ian did a beautiful job, and Keith Jarrett never sounded better, thanks for the private audition at AkFest! Jay - 8532's are essentially "ruggedized" 6J4's or 6J4WA's. If I recall correctly, "rocket boy" Bob Danielak chose them because they were cute and small along side the 1626's and...
  12. Gary Kaufman

    Heathkit a-9 amp

    The schematic with voltages is on HifiEngine at http://www.hifiengine.com/library/heathkit/a-9c.shtml You'll need to register to download the file. - Gary
  13. Gary Kaufman

    ST-70 in Triode mode

    It probably won't make any difference, or you can parallel two of them (75 ohms) which will work nicely. Alternately you can PM me an address and I'll toss 4 100 ohm resistors in an envelope for you. FWIW, it's never been a modification that I've liked the sound of, but it's easy to reverse...
  14. Gary Kaufman

    Balance problem on tube amplifier

    Happy to help you test the tubes, PM me and we can pick an evening. Also if you can post a pic of the selenium rectifier I can get you a terminal strip that will fit into the space and a 1N4007 for the replacement. - Gary
  15. Gary Kaufman

    Balance problem on tube amplifier

    Don't worry about adjusting the bias resistor to start. A bit more negative won't hurt - if anything you'll get a bit less power and the output tubes will run cooler. - Gary
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