This is a Ramn 500 monoband hf amplifier I repaired. It was picked up in a trade, and needed a good bit of work.
This was built somewhere around 1975, and no schematics exist on the web, that I could find. I reverse engineered the circuit as best as I could, correcting for hacks and changes over the last 50 years. This uses 2ea 8950 compactron tubes, driving 4ea 8950 compaction tubes. It runs about 1100 vdc on the plates, 550 vdc on the screens of the driver tubes, and a variable -20 to -50 vdc on the control grids. It has an inductive adjustable tuned input for input matching.
As seen in the 1st video, the driver tubes were red-plating in about 10 seconds of key up with no rf drive. The final tune control had lost chassis ground, the negative bias supply was not functional (due to a mis-wired transformer winding), the capacitor bank was mis-wired (too many caps in the 1100vdc circuit, and not enough in the 550vdc circuit), the transformer HV center tap lacked a diode at the connection point of the 550 vdc cap stack, the final tank circuit was wired DIRECTLY to the antenna output connector (!!!) instead of being routed through the changeover relay, the rf input circuit to the driver tubes was broken and blowing in the wind (and missing a coupling cap), RF and DC grounds were lugged under the bolts that secure plastic feet and were ALL loose, the PA output coax was melted and mis-wired, etc. I added an additional ground for the transformer and main control board, the ventilation slots in the upper cover were mostly blocked and had an AC fan with dangerous wiring. I removed the shroud, changed it to a DC whisper fan with reduced speed/sound, and installed a stainless steel fan cover.
Here's some pics with info, and videos...
Stainless steel fan cover installed...
