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  1. Replies
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    I star grounded the power supply, preamp and all...

    I star grounded the power supply, preamp and all except the output tubes in the Workhorse 30 and 60W versions. It takes some thinking. the basic idea came out as running a batch of parallel ground...
  2. As Mark points out, the Magnatione...

    As Mark points out, the Magnatione vibrato/tremolo effect is a variant of phase shifting. If you're a circuits kind of guy, you can look at the schematic and see that it's a phase shift stage much...
  3. Thread: HV SS Regulators?

    by R.G.
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    1,119

    Waaa-hoooo! Great! I was beginning to think I'd...

    Waaa-hoooo! Great! I was beginning to think I'd led you down the garden path or up the creek.

    The MOSFETs are probably OK at 50C. Those suckers are OK with junction temps up to about 175C.
    ...
  4. Thread: HV SS Regulators?

    by R.G.
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    1,119

    OK then. Max current in a 1.3W 68V zener is going...

    OK then. Max current in a 1.3W 68V zener is going to be 1.3/68 = 19ma. Absolute minimum Rgs is then 5V/19ma = 261 ohms. It's a conservative idea to not go above half the power dissipation, so that...
  5. Thread: HV SS Regulators?

    by R.G.
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    1,119

    You're hitting some of the asterisks and...

    You're hitting some of the asterisks and footnotes to the design I mentioned. :) Let's dig in.
    The MOSFETs I suggested are FPQ2N80's, and they specify a Vgs threshold of conduction of 3 - 5V. Any...
  6. Thread: HV SS Regulators?

    by R.G.
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    1,119

    Oscillating?? Yipes! I'll go do some thinking...

    Oscillating?? Yipes!
    I'll go do some thinking and model running. This has to be some kind of interaction between the current source and the zeners.

    Next shoot-from-the-hip possible cure: leave...
  7. Thread: HV SS Regulators?

    by R.G.
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    Actually, I meant just across the zeners...

    Actually, I meant just across the zeners themselves.
    Reverse-avalanched junctions make noise. Many classic noise sources start with a zener run at low current and then amplify that. Feeding a zener...
  8. Thread: HV SS Regulators?

    by R.G.
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    1,119

    I've been resisting the urge to ask how it's...

    I've been resisting the urge to ask how it's going with these. :)

    I can speculate that maybe this is the inherent zener noise being buffered by the MOSFETs. My first step would be to put a cap...
  9. Thread: HV SS Regulators?

    by R.G.
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    1,119

    Sorry - I didn't check back in for a couple of...

    Sorry - I didn't check back in for a couple of days.

    I think it's the drains that are connected to the back/tab of the MOSFETs, but that is effectively the same problem. If I were building this,...
  10. Thread: HV SS Regulators?

    by R.G.
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    1,119

    Dead right, that.

    Dead right, that.
  11. Thread: HV SS Regulators?

    by R.G.
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    1,119

    I use that technique a lot myself. ;) The...

    I use that technique a lot myself. ;)

    The answer is yes, it's easy. The current limiter can easily be set to let through more current. R3 is 39 ohms for a total of 15ma. You can twiddle that...
  12. Thread: HV SS Regulators?

    by R.G.
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    Here's an updated schemo and BOM. I can send more...

    Here's an updated schemo and BOM. I can send more detail on the layout if you need it.

    58226
  13. Thread: HV SS Regulators?

    by R.G.
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    1,119

    Works fine. You can take that and run with it if...

    Works fine. You can take that and run with it if you like, or we can just iterate a couple of times and I'll send you gerber.

    More considerations:
    I need to make you up a parts list. Some of the...
  14. Thread: HV SS Regulators?

    by R.G.
    Replies
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    1,119

    OK, just checking. It gets much smaller with SMD,...

    OK, just checking. It gets much smaller with SMD, but I thought I'd ask.

    Next: PCB style. I laid out both circuits on the same sized PCB, 2.8" x 1/8". The power density is the same, but of course...
  15. Thread: HV SS Regulators?

    by R.G.
    Replies
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    1,119

    Can it stand 0.4" high?

    Can it stand 0.4" high?
  16. Thread: HV SS Regulators?

    by R.G.
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    1,119

    Hmmm. Next question: Can you solder surface mount...

    Hmmm. Next question: Can you solder surface mount parts? I can make it a lot smaller that way.
  17. Thread: HV SS Regulators?

    by R.G.
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    1,119

    That's good enough to start with. I think I can...

    That's good enough to start with. I think I can suggest a layout that keeps it in that volume.

    Is there some chance of putting a baby board on top of the original circuit board to hold this?
  18. Thread: HV SS Regulators?

    by R.G.
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    You know you're going to get an engineer's...

    You know you're going to get an engineer's response to that, right? :)

    How tight is the space? Got pics and measurements of the volume to put it in?
    and...
    To a certain extent, you're going to...
  19. Thread: HV SS Regulators?

    by R.G.
    Replies
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    1,119

    OK, first pass design done. Two options: 1....

    OK, first pass design done. Two options:
    1. Active current limiter and string of 5W zeners. Works OK, but probably sloppy voltage tolerance. May not be cheaper than the more complex variant, but is...
  20. Thread: HV SS Regulators?

    by R.G.
    Replies
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    1,119

    Mmmmm. Forgot to say - what's your budget...

    Mmmmm. Forgot to say - what's your budget constraint? A quick look at MOSFETs that will (probably) do the job looks like they run to $1.20-$2.00 each from Mouser.
  21. Thread: HV SS Regulators?

    by R.G.
    Replies
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    OK, got it. How close to the nominal output...

    OK, got it. How close to the nominal output voltage do you think it needs?

    MOSFETs have "infinite current gain", but the Vgs, analogous to Vbe in bipolars, is a few volts, and increases at about...
  22. Thread: HV SS Regulators?

    by R.G.
    Replies
    40
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    1,119

    None of this is any problem. I can zap you up a...

    None of this is any problem. I can zap you up a circuit.


    Sounds like it was marginal to begin with. Show me the original schemo or tell me what the various output voltage levels are, and any...
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    It's a question of objectives. What does the...

    It's a question of objectives. What does the owner want the amp to do? Here are some possibilities.
    1. Be original; this one is easy. Don't do anything to it. It stays original.
    2. Work; in this...
  24. I did say "properly crimped".;) That's always a...

    I did say "properly crimped".;) That's always a challenge.

    I'm doubtful of the typical auto-parts store crimping equipment, too. However, a properly crimped connection - folded, pressed to the...
  25. The Thomas Vox Westminister shares a lot of...

    The Thomas Vox Westminister shares a lot of things with the Buckingham, Guardsman, and Beatles. One of these things is a very outdated grounding system. It is fairly difficult to get these things...
  26. Bill Bryson, "The Mother Tongue: English And How...

    Bill Bryson, "The Mother Tongue: English And How It Got That Way"
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    It would be very unusual for the wiring to be...

    It would be very unusual for the wiring to be steel, but I guess it's possible. More likely it's tinned copper. As Helmholz notes, a magnet tells the tale.

    Solder plated steel has been used for...
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    The cheaper Asian restaurants often have...

    The cheaper Asian restaurants often have paper-wrapped pairs of chopsticks simply sitting in containers on tables or at the cutlery pickup. The two sticks are still joined at one end and you snap the...
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