I purchased a Hickok PS-505 on eBay that is in excellent shape! All of the outputs worked except 400VDC. I opened it up and the 400VDC regulator PCB was missing. It consists of an HV transformer with a variac on the primary side. This gives me 0-600VDC after bridge to the regulator PCB. The PCB has a pair of series 2N4240's mounted on an external heatsink that are controlled with a CCS-driven error amp and an SCR protection circuit.
Replicating the PCB will be tough as it is a card-edge that plugs into a connector.
I was wondering if anyone knew of a regulated power supply module, kit, etc. that was capable of tracking the input voltage (minus a dropout) that I could drop in off of the variable 0-600VDC output of the transformer?
The original supply is 0-400VDC at 150mA which is fine for my needs. I can repurpose the 6x8" aluminum heatsink for a series device or re-use the transistors already there. Attached is the schematic and PCB-2 is what is missing. There is also a 40k pot ganged to the variac to allow the -100V bias supply to track with the 400V supply but I do not need that functionality.
Replicating the PCB will be tough as it is a card-edge that plugs into a connector.
I was wondering if anyone knew of a regulated power supply module, kit, etc. that was capable of tracking the input voltage (minus a dropout) that I could drop in off of the variable 0-600VDC output of the transformer?
The original supply is 0-400VDC at 150mA which is fine for my needs. I can repurpose the 6x8" aluminum heatsink for a series device or re-use the transistors already there. Attached is the schematic and PCB-2 is what is missing. There is also a 40k pot ganged to the variac to allow the -100V bias supply to track with the 400V supply but I do not need that functionality.
Hard. If it tracks the input voltage, it wouldn't be a regulator, and replicate any ripple etc on the input.
Probably in the original the input voltage/variac was coupled to the output voltage setting. If so, you could use any variable output regulator and feed its reference from the rectified and smoothed input voltage, while the reg itself is fed from the raw rectified voltage.
BTW what is the issue with replicating the original PCB? Plug-in card fingers are a standard PCB 'part'.
Jan
Probably in the original the input voltage/variac was coupled to the output voltage setting. If so, you could use any variable output regulator and feed its reference from the rectified and smoothed input voltage, while the reg itself is fed from the raw rectified voltage.
BTW what is the issue with replicating the original PCB? Plug-in card fingers are a standard PCB 'part'.
Jan
No.
The -105V is fixed, the main reference.
The 40K and the Variac are ganged SO THAT the raw DC voltage is slightly-higher than the desired DC voltage. This limits stress and heat in the pass transistor. Imagine: full 500V raw DC input, 0.2A current limit, you turn the 40K down to say 50V. The pass transistor sees 500V-50V= 450V, 90 Watts, which is far too much for a TO-3 on a practical heatsink. Instead, to turn the 40K to 50V you must also turn the Variac down to say 70V raw DC, the pass transistor sees 20V and 4 Watts.
Rig Q5 Q6 as a cap-multiplier. (MOSFET may be the modern way to go.) Turn the Variac so the raw DC is a hair higher than desired DC. (The 40K is not needed.) The cap-multiplier will filter the ripple and quick-term dip/spikes. A $9 DMM on the output lets you know the output is stable (it will be pretty close, in most homes/shops, for not-large changes of load). Not fully As Original, but plenty useful.
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