• Country
• Great Britain (UK)

• Manufacturer / Brand
• Homebrew - ORIGINAL; GB

• Year
• 2018/2018

• Category
• Miscellaneous (Other, Various) - see notes

• Radiomuseum.org ID
• 304315

Click on the schematic thumbnail to request the schematic as a free document.

• Number of Tubes
• 3

• Valves / Tubes
• PY500A PY500A 1941A

• Main principle
• none

• Power type and voltage
• 35 Volt

• Loudspeaker
• - - No sound reproduction output.

• Power out
• 3000 W (5000 W max.)

• Material
• Metal case, TUBES VISIBLE

• from Radiomuseum.org
• Model: Spotwelder Mk.1 [2] - Homebrew - ORIGINAL; GB

• Shape
• Book-shelf unit.

• Dimensions (WHD)
• 240 x 213 x 136 mm / 9.4 x 8.4 x 5.4 inch

• Notes

• This is a spotwelder I made from an old PC supply box for spotwelding battery terminals to batteries and doing other low-power welds. Basically has a full-wave rectifier using x2 PY500As, which have extremely low internal (45.5 Ohm) resistance, therefore I chose them.

  This circuit goes through a 5.45H choke and feeds into a 70s 35WVDC 45surge 27000uF capacitor. Judging by the size of the capacitor and being taken out of a vehicle diagnostics unit, I safely assume it can handle way more current than any modern one.

  After the choke the voltage is much less than the original 35V, and to get the capacitor to 35V takes a long time from parasitic capacitor inductance, the ripple is very low after that (relatively to voltage) massive choke value. That + the parasitic resistance of the choke (151.8 Ohm) makes the current after 25V becomes really low, so I added a bleeder resistor and a POT to fight the parasitic voltage increase.

  This was done so I could have different voltages on the capacitor for different power output, so I don't melt delicate wires I weld to small batteries. The bleeder can be switched off with a switch at the front, so the voltage slowly rises to 35V, where it pretty much stops.

  The PY500As have a 42Vf @ 0.3Af and are designed for filament chains, which is what I did, with a 1941A ballast tube/barretter/iron-hydrogen resistor.

• Net weight (2.2 lb = 1 kg)
• 6 kg / 13 lb 3.5 oz (13.216 lb)

• Price in first year of sale
• 250.00 £

• Author
• Model page created by Yaroslav Voronov. See "Data change" for further contributors.

• Other Models

• Here you find 41 models, 19 with images and 7 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
  All listed radios etc. from Homebrew - ORIGINAL; GB