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In Reply to: RE: More questions regarding voltage regulator tubes posted by firstname.lastname@example.org on August 05, 2017 at 05:04:41
Just use a much larger (in terms of wattage rating) resistor than the calculations yield and the heat will be nicely spread out. For what you're doing, the regulator is worth it sonically.
After about 3 hours of operation the top plate was very hot. At this stage I was committed to using this chassis so I drilled many holes in the top plate but it did not seem to make any difference with regards to temperature. I used a 5K 25 watt resistor and a 3.5K 25 watt resistor, both chassis mount so no problem in terms of power rating. However heat is still heat and seems to build up. There is also 4 ohm 50 watt filament bias chassis mount resistor that dissipates about 6 watts. No room for a fan really and are noisy and cheap ones fail quickly.
The problem I believe is that the way I attempted to bias the tube fitted the plate curves which do not seem to be very accurate. At -5V bias, 150 plate volts and 10ma the VR tube should not have had to work very hard. At this bias and current the tube would prefer to see 170V. So I think that the VR tube is drawing a lot of current trying to maintain 150V and consequently the series resistor is generating a lot more heat than the "average".
If my understanding is incorrect please let me know. All I know is that having removed the VR tube from the circuit and using appropriately sized resistors to get my plate voltage results in greatly reduced heat buildup.
Chassis mount resistors are garbage in terms of the power they can actually dissipate. I'd recommend reading the entire datasheet on a well documented one like the big Vishay/Dale ones. You'll end up seeing a chart of what they can handle without a chassis, and at some point you should also end up seeing what they consider a "chassis", which may be a 12"x12" piece of aluminum 1/4" thick.
Xicon has some 25W wirewound resistors that aren't too expensive and are easy to find on Mouser.
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