Tube Question

[pimphand442]

on this skipper 300 I have a driver tube that is bad and was wondering can I just drop a 6lf6 or a 6hf5 in and drop the voltage on that tube or no?

 

[Shockwave]

The answer is YES! If the amp used 8950 tubes with 12 volt filaments you'll need to shave off half of this voltage to light the 6.3 filament in the 6LF6 tube. Ohms law tells us this would require a 3.15 ohm 12.6 watt resistor. Not the most standard value but it could be done. I think the easier way would be to place some diodes inline with the filament to drop the excess voltage there. This will also make the warm up time on the 6LF6 the same as the other tubes since there will be no current limit through a resistor on start up.

I'd start with stacking about 10 diodes inline with at least a 3 amp rating. Start with more diodes than you need so you don't damage the filament with more voltage during testing and remove one at a time until you have as close to 6.3 volts across the filament as possible. As the tube warms up, filament voltage will rise slightly until it's at full temperature. Make sure you wait at least 60 seconds before measuring the voltage or it could be set too high. You will be feeding the filament with pulsed DC but with tubes that use an indirectly heated cathode such as sweep tubes, it's a none issue.

Note: This assumes the amp uses a 12 volt filament transformer and all filaments are wired in parallel. I'm nearly sure this is the case. If it is a series configuration, this will not work since the 6LF6 draws twice the current as the other tubes and current in a series circuit is the same throughout the circuit.