Ampex 351-2 restoration project

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Comments

  • That measurement was taken with the power supply in-circuit, full load.
  • txcoastal1txcoastal1 Posts: 9,602
    Cool, just was wondering...keep us posted

    TFS
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  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    Let me make sure I'm correct. The previously measured 0.7 volt drop was actually across a 2.54 ohm resistor not a 1.5 ohm resistor, correct?
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • I measured the 12.87 VDC with the power supply connected to the circuit so I don't think it would drop -- but let me know if I am missing something.
    thanks!
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    A few posts ago you measured a DC voltage drop of 0.7 volts on either side of 3R-60 that you assumed was 1.5 ohms. But once you pulled 3R-60 from the board you measured at as 2.54 ohms meaning that the actual voltage reduction was across a 2.54 ohm resistor instead of an assumed 1.5 ohm resistor. That means a different amount of current is flowing through the circuit.
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • Yes, Ken, your previous statement is correct. Should I again measure the current flowing through the circuit? BTW: this is all with the original power supply board in-circuit. I have yet to install the new power supply board...so I am wondering if other components on the original power supply board were also out of spec(?).
    thank you both!
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    Yes, now that you know the actual value of 3R-60 put it back in the circuit, turn it on and let it stabilize for a few minutes and place your DC meter on each of the resistor's leads. Measuring what the voltage drop is across the resistor. Then take that voltage and divide it by the resistor's value. Now we will know the amount of current flowing in that circuit.
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • Thanks Ken I will do so, and report back!
  • Hello!

    I recently acquired a 351-2 and although it is in decent shape, it needs some recapping. I just opened up the bottom of the motor/transport section and saw the motor caps are leaking everywhere.... I was going to go ahead and order new caps across the board, but am having trouble finding these motor caps. any leads?


    Adrian in Richmond, VA
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    Hello Adrian,
    Be careful of any leaked material from those capacitors, try to dispose of it carefully. The supply and take-up values are 3.75uF and the capstan motor is 5.0uF with a voltage rating of 375VAC or higher. Several years ago I found them at Grainger.com
    I hope this is helpful.
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • NorthamusiNorthamusi Posts: 23
    Hi Ken:
    Had the chance to sit down with this today... First I measured 3R60 out of circuit. It measured 2.1 ohms (I'm not sure why it would measure different from last time. I used the same meter and also checked it on a second meter). The voltage drop across 3R60 was 0.8 volts. So current flowing through the circuit is 0.38 A, correct? Please let me know what you think.
    These measurements were all made with the old power supply, which I plan to replace with the new PCB I constructed.

    thanks for your insight!
    Steve
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    Hi Steve,
    The original goal was to drop the voltage by an additional 0.6 volts, giving a filament supply of 12.6 volts. The voltage drop goal would then be 1.4 volts, so 1.4 divided by 0.38 ampere gives a resistance of 3.68 ohms.
    It looks like Digikey has a 3.5 ohm 10 watt, mil-spec resistor in stock with a part number of: MRA12-3.5ND for around $5.00 that would work.
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • NorthamusiNorthamusi Posts: 23
    Thanks Ken, much appreciated!
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    Good luck with everything!
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • NorthamusiNorthamusi Posts: 23
    I will of course, keep you posted!
  • NorthamusiNorthamusi Posts: 23
    The power supply is complete! (the rectifier tube is not in place in this photo)vjhc8iidebph.jpeg

    Next step is removing the old PS board and installing the new one.
  • NorthamusiNorthamusi Posts: 23
    Success! The power supply is installed and the unit is operating properly. Filament supply is 12.5 volts, which I think is pretty darn close. Here's a photo

    o3tkh4p6wwvg.jpeg

    Next I'll decide how to proceed with the record and playback cards. I think I'll rework the original cards instead of replacing them with new ones. Also just ordered a piece of perforated sheet metal so I can fabricated the missing "cage" cover for the top.
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    Very well done, looks great!
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • NorthamusiNorthamusi Posts: 23
    Thanks Ken!
  • KennethSwaugerKennethSwauger Moderator Posts: 6,401
    No problem, what's next?
    "And the house you live in will never fall down
    If you pity the stranger who stands at your gate" G.Lightfoot
  • NorthamusiNorthamusi Posts: 23
    I just bought a perforated stainless steel sheet to make a 'cage' cover for the missing one. I guess that's next. I'll also start making a list of what I need to rebuild the record and repro boards. I think I'd rather refurb the old circuit boards as opposed to replacing them with new ones. I'm hoping to work on this a little more regularly in the coming weeks.
  • NorthamusiNorthamusi Posts: 23
    Here are photos of the sheet, prior to any cutting. It's 20 gauge stainless. Not sure how I'll go about cutting this... I may use a Dremel tool.

    7aj0q3hqbu0y.jpeg

    yp2rebipk778.jpeg
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