100 ohm resistors for filament ground reference burning up
Moderators: pompeiisneaks, Colossal
Re: 100 ohm resistors for filament ground reference burning up
At least fish paper, or PTFE, instead of cardboard. BTW anyone use those super expensive nylon/gold tube sockets?
Tube junkie that aspires to become a tri-state bidirectional buss driver.
Re: 100 ohm resistors for filament ground reference burning
Heater-to-cathode short?Phil_S wrote:Sounds like an intermittent short. Look for it. Could be a wire whisker, insulation problem, something else? A magnifying glass might be helpful.sbirkenstock wrote:I put 100 ohm resistors for the filament ground reference in my amp project. Once in a while they just burn up....
What would cause that?
He who dies with the most tubes... wins
Re: 100 ohm resistors for filament ground reference burning up
I can see that a heater-cathode short would put a lot of current through those ground reference resistors when in cathode bias, but not when the cathodes are grounded in fixed bias mode?
I think there's a strong argument for having those resistors of a sufficient power rating that the heater ground reference has some chance of being maintained in such a fault condition, at least for a few seconds, until a fuse blows.
Otherwise all the tubes may have their heaters pulled up towards VB+, to the detriment of their heater - cathode insulation, leading to a bunch of tubes that allow a potentially significant degree of heater current into the signal path, leading to a buzzy interference.
I suggest / use wirewound types of at least 3 watts, with a 500V surge capability.
I think there's a strong argument for having those resistors of a sufficient power rating that the heater ground reference has some chance of being maintained in such a fault condition, at least for a few seconds, until a fuse blows.
Otherwise all the tubes may have their heaters pulled up towards VB+, to the detriment of their heater - cathode insulation, leading to a bunch of tubes that allow a potentially significant degree of heater current into the signal path, leading to a buzzy interference.
I suggest / use wirewound types of at least 3 watts, with a 500V surge capability.
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
Re: 100 ohm resistors for filament ground reference burning up
Anode to heater flashover - as Leo describes - it's not too uncommon. I've seen 1960's guitar amps with a short length of spaghetti slipped over pin 3 and glued to base to increase creepage (factory installed). That was just one of many mods the factory installed to make the amp 'road ready' and somewhat bulletproof.