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Tube Amp Power Supply for test fixture

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  • Tube Amp Power Supply for test fixture

    Years ago, I had picked up this 2U Tube-based DC Power Supply that looked useful for some project work yet to happen. I thought I had logged it into my inventory database where I recorded the purchase info and details of the item. Must have skipped that step. Probably paid around $50 from C & H Sales in Pasadena in the mid-90's, I'd guess.

    I had moved it to my shop at CenterStaging at some point having set up the repair shop here. I dug it out of it's hiding place in the shelves, and opened it up for a closer look. All I had ever done with it before was to replace the frayed 2-wire power cord with a 3-wire cord.

    There were two axial electrolytic caps was 12uF/450V, the other was 12uF/600V. Date code I found on the 450V part was 6013 (1960, 13th week). Tube compliment is a 5Y3 Rectifier tube, 6BX7 Dual Triode, 0G3 Voltage Reference tube and a pair of 12AX7's. I brought up the AC Mains slowly, with DMM acros the 12uF/600V part. I hadn't yet discovered there was a schematic on the top inside panel. Found that today. By the time I got to 120VAC, there was 575VDC across that cap, so DO need a 600V cap. I recalled having a 20uF/600V Sprague Atom cap that I had purchased for use during restoration of a Sunn 1200S, though ended up using a different set of caps, so it was available. Much longer part, so mounting would left to gluing it down and to the F & T 22uF/500V part that I used to replace the 12uF/450V part.

    Completed the cap installation this morning, then powered it up to see what I had. That was when I found the schematic

    Trans Elecronics RS 305 Schematic.pdf

    Unloaded, the DC output range is 230VDC to 385VDC. I haven't had the scope on it to see the ripple left on the output, but the Fluke showed around 65mV. With it good for 50mA load, and the 6.3VAC Heater rated for 3A, this will be more than suitable for the test fixture to screen/sort 12AX7's, 12AT7's, 12AU7's, 12AY7's and other Octal Triodes like 6SN7's, 6SL7's.

    Click image for larger version

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    I see on the maintenance sticker next to the 6BX7 Pass Tube all the tubes were replaced 6/19/72. I haven't replaced the molded plastic 47nF/400V cap, though I do have new Vishay MKT 47nF/400V parts to do so. The Electrolytic caps definitely needed replacing. I like the power xfmr secondary, as there's separate heater for the 6BX7, then one for the two 12AX7's, and a separate 6.3VAC w/CT for the external load.

    I'll see what I find once I get to cobbling together the Preamp Tube fixture and see if this is clean enough to use. I do like the Birtcher Type 926B Octal Base Clamps installed. I've never seen those before, apart from on this supply. Very well made part. Wonder what happened to that company?
    Attached Files
    Logic is an organized way of going wrong with confidence

  • #2
    I found some Birtcher clamps like this on ebay, priced way too high. More from one or more sources that also will want an arm and a leg, but then found this site where they DO have some similar to them...Birtcher parts, though not 926B's. And properly reasonable prices. I'd assume surplus/NOS.

    Logic is an organized way of going wrong with confidence


    • #3
      I ordered a bunch from New Sensor years ago, I think they were reasonable.

      That's a good idea I was thinking of building, since I have several used tubes that may be okay to use for now until new replacements are available at normal prices.


      • #4
        if you aren't wedded to a perpendicular mount these work great and cushion quite a bit.
        Click image for larger version

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        The silicone versions handle big bottle tube heat well also