Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Chuck -
You could, but the fuse would have to be able to clear the 650V B+ to open the circuit. A fuse that is RATED to do this is about six inches long and costs about $5 each. The KWS-1 uses one in it's power supply. This problem is why Drake used the 0.82 ohm resistor in the L-4B power supply. It just explodes if the HV (2800 VDC) gets shorted!
This was a good discussion, brought out some ideas which were shot down for various reasons. I must confess that I ran three B-lInes 24 x 7 for about five years in autostart teletype service with no failures. Keep in mind that the ONLY failure scenario that affects this is if the bias supply ONLY fails completely and suddenly. As Gary said that doesn't happen very often. I've been running a LOT of Drake gear with a LOT of AC-4 power supplies for many hours over the last 40 years, and it hasn't happened to me, yet.... I only KNOW of it happening a half dozen times over all those years, including Gary's. Usually bias supplies present first with increased ripple, drifting Final idle current, VOX hanging, etc.
Probably the best answer is a relay in the primary circuit that has to be pulled in by the bias voltage to power the supply. This could also serve to reduce the wear and tear on that difficult to replace power switch in the T-4X/TR-4. There would have to be a provision to 'over-ride' the relay to close it until the bias voltage was present, but that's not insurmountable.
I think the best "practical" answer is to replace those bias filter caps that are 40 years old with new ones, and if you leave the room for any length of time, turn it off. Also, if you start to notice weird VOX action, hum on the CW signal, etc., check out the power supply!
73, Garey - K4OAH Glen Allen, VA Chuck Grandgent wrote:
Thanks Garey, am replying directly as might seem like beating a dead horse at this point. Can we fuse the cathode ? Sorry to be a pain... Chuck, K1OM
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