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RE: More questions regarding voltage regulator tubes

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.


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  Kimber Kable  


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