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why does 1 amp run hotter than another
why does 1 amp run hotter than another
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Old 7th October 2014, 12:35 AM   #1
muscmp is offline muscmp  United States
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Default why does 1 amp run hotter than another

i have 2 gibson ga79rtv amps. they both sound excellent. however, one runs considerably hotter than the other. what could cause this?
thanks,
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Old 7th October 2014, 12:51 AM   #2
kevinkr is offline kevinkr  United States
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why does 1 amp run hotter than another
Moved to Instruments and Amps per forum policy. More likely to get an answer here anyway.

Classic Amps: The 1961 Gibson GA-79RVT
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Old 7th October 2014, 01:38 AM   #3
Enzo is online now Enzo  United States
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Different levels of bias, different tubes, leakier coupling caps on one.
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Old 7th October 2014, 01:38 AM   #4
Vasquo is offline Vasquo  United States
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Oscillation
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Old 7th October 2014, 01:49 AM   #5
JMFahey is online now JMFahey  Argentina
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Although oscillation is not impossible, it would sound fuzzy or funny.

I'd cast my vote for different biasing=different tube current/dissipation.
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Old 7th October 2014, 01:49 AM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by muscmp View Post
i have 2 gibson ga79rtv amps. they both sound excellent. however, one runs considerably hotter than the other. what could cause this?
thanks,

Check the 200 Ohm cathode resistors and the output tubes.
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Old 7th October 2014, 02:06 AM   #7
shanx is offline shanx  Canada
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Consider yourself VERY lucky for owning 2 of those beauties. If someone wants to part with a GA40..I would be happy most happy to oblige. Long story of a lost love....
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Old 7th October 2014, 02:18 AM   #8
rayma is offline rayma  United States
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Quote:
Originally Posted by Enzo View Post
leakier coupling caps on one.
Yes, that's quite possible. Check the voltages at the output tube grids, which should be close to zero.
If one or more grids are at some significant positive voltage, replace the coupling capacitors.

Last edited by rayma; 7th October 2014 at 02:22 AM.
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Old 7th October 2014, 03:52 AM   #9
muscmp is offline muscmp  United States
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thanks to all. it looks like i'll check and possibly replace the coupling caps.
thanks again,

play music!
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Old 9th October 2014, 04:07 AM   #10
muscmp is offline muscmp  United States
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thanks to all, i've replaced the coupling caps and the amp doesn't run nearly as hot.

thanks again,
mikeB.
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