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Old 15th February 2009, 09:34 AM   #1
diyAudio Member
Join Date: Dec 2007
Default how hot is 2n3055 can go?

hi guys

i check the datasheet. it said 200 deg celcius. but i just wanna double check with you guys and whats your recommendation.

the psu i am using is rated 3A, while the tubes only draw 1A when AC. not sure how much it gonna draw the current if DC supplied.

i am using 2n3055 to boost current to use for tube heater supply. it run very hot. i use quite a big heatsink 100mmx100mmx30mm. which sell locally to mount 2 pcs of 2n3055. but i only use one here but i cant put my finger on the heatsink. is this normal?

i connect a 25vdc to the ground of this psu for heater supply to float the heater voltage as recommended. is this that cause the hot?

thannks in adv

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Old 16th February 2009, 07:51 PM   #2
diyAudio Member
Join Date: Jul 2003
Location: Bath, UK
150degC is considered the service limit for silicon, and at that lifetime is very, very short. Remember that's the junction temperature...not the case, which has to be kept cooler owing to the thermal resistance from the silicon die to the case.

In practice - a good service limit on temperature is when you can just bear to touch the case - that's about 55-60degC case temperature.

- And in many circuits the ideal running temp will be cooler than that since reliability, noise, current gain (Hfe) and so forth all suffer at higher temperatures.

Floating the heater supply should not cause you a problem, but what is the raw heater supply voltage? Can you reduce it? Or look for a bigger heatsink!
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Old 17th February 2009, 01:32 AM   #3
diyAudio Member
Join Date: Dec 2007
hi Martin

input dc is 23vdc. yes i think i can reduce the input. whats the input dc voltage do you suggest? 14vdc?

run them around an hour. both heatsink is untouchable. the transformer rated for 3A also untouchable. dont know the va of the PT, as the secondary has several outputs. 36v ct, 30v ct, 24v ct. but i think the PT is more than enough to do the 1A required for the heater supply.

i disconnect them as i think i will toast them if i go on.

i think the heatsink i use it quite big(rated for 2 pcs of 2n3055). but i will try bigger one(rated for 4 pcs of 2n3055) hence double the size of the one i am using now.

hmm though the floating that may cause the supply.

got this psu kit locally here. its rated for 3A adj from 5-15vdc. its using 16 pins chip, forget the type. will try to scan the schematic and post here.

thanks for the help

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