Power scaling on a budget

Discussion in 'Amp Tech Center' started by LightningPhil, Jan 22, 2020.

  1. LightningPhil

    LightningPhil Tele-Meister

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    Nottingham, UK
    The daughter's first soldering lesson today - tinning copper wires for a power scaling experiment. Once I'd dialled it down to sub 1 W levels, she asked if we can make it really loud again. Awesome!

    Maybe power scaling isn't required. But if anyone wants to give it a go, these little SMPSUs are great:
    https://www.ebay.co.uk/itm/High-Vol...V-390V-ZVS-Step-up-Charge-Module/292914470534

    We (I) soldered the output directly across the main bus capacitor in a Pro Junior and "carefully" disconnected the HT output of the power TX. That way the voltage from the module would power everything interesting and the power TX would continue its job with the heaters.

    Prior experiments were on an AC30, and there, I found that 6 dB or so could be trimmed off the volume and it still worked well, but from there on down, the tone changed as well as it getting quieter. The pro junior behaved similarly, though without much volume or tone change to start with.

    No science was done and no notes were taken, so can't mention voltages. Other than started at a fairly stock 330V and met quiet mud tone at about 75V. Middle ground was interesting.

    There was no noticeable noise what so ever from the module, even when running the amp at full voltage and the volume knob turned all the way up. Quite impressive!

    So now I'm tempted to remove the board mounted pot and replace it with a remote single turn one with a limited range of control (resistors on the pins so the settings can sweep from 330V down to 100V or so). An old laptop power supply could run it and supply ample power for heaters also (via another regulated step down module).
     
  2. kbold

    kbold Tele-Afflicted Silver Supporter

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    What copper wires was she tinning?: not the ones for terminal connections, I hope.
     
  3. LightningPhil

    LightningPhil Tele-Meister

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    Nope, I use 3 in one oil on them to make it easy to slip into the crimps. Tinning after application of oil makes it catch fire :cool:

    It was the wires I then soldered onto the bus cap’s leads. Meant not taking the board out. While a bodge, was removed after the test.

    The spade connectors on the power side of the Pro Junior are all for configuring the export TX (as the manual describes it). Bit strange that the HT connection is soldered. Quite a rats nest, so they’ve been pruned back, made permanent and neatly heat shrink wrapped, while the remaining wires that needed to be connected to make use of the fuse and switch were neatly dressed. Doing the same to the heater wire and the LED one all helped reduce hum a bit.
     
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