Heater anomaly

LarryN

Member
Messages
955
I bought a Crate GT-50 combo for clubs gigs for $100. It seems to function fine, bit I measured the filaments and one side is 4 plus volts and the other, 1.8 volts. Is there anything i can do to correct this? Also, the highest the bias voltage will go is 31 volts, which seems a little low. (4X6V6's) I'd appreciate any help I can get. Thanks.
 
Messages
826
The filament voltage sounds OK to me. Each tube wants to see 6.3Vac from heater pin to heater pin, so 4+1.8 = 5.8 is 'close enough'. The voltage from each side to ground would depend on how the heater circuit is referenced to ground. If there is a 'humdinger' pot for example, it can be adjusted away from the half-way position (which would give 3.15Vac on either side) to give minimum hum.
 

LarryN

Member
Messages
955
I just noticed the resistors at the end of the filament traces, one is 100 ohm and the other 47 ohms. I'm wondering if it was a production error or intentional. Should I assume the tube doesn't mind unequal voltages per side, as long as it's in the 6 volt ballpark? Thanks, Malcolm.
 
Messages
826
I just noticed the resistors at the end of the filament traces, one is 100 ohm and the other 47 ohms. I'm wondering if it was a production error or intentional. Should I assume the tube doesn't mind unequal voltages per side, as long as it's in the 6 volt ballpark? Thanks, Malcolm.
That's interesting. Could be a production error, or could be 'designed in' to get that 'minimum hum' sweet spot. The tube won't mind, so I think I would leave it (since you are happy with the hum level anyway).
 

LarryN

Member
Messages
955
Cool, that's kind of what I was thinking. No second guessing engineers for me! Thanks a bunch from the colonies, Malcolm.
 






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