Thunderbolt 305 rebuild questions-

[rumrunner]

My dependable old 305 crapped out - (power dropped to about 200 watts). I replaced the 6lq6's with new sylvania 31lq6's series stringing the fils for mains power with a separate switch and 3 amp fuse. Burned new toobs in for about an hour on just fil's then cut in the hv on standby for a few then power up, key down and tune. now I got about 250-300 watts and what has been described by a friend as a 60 cycle hum in the audio. My best guess is I lost a filter cap that dropped my power when it went out on a bad Dx contact and was never told it did anything funny. New caps are ordered. I understand the plate voltage should be from 700-850 volts?? I also need to know if their is any bias procedure for the new toobs? Any of you Guru's have any info about what the voltage should be and what kind of outpoot I should expect and also any pointers on this box? I drive it with a 440 Stryker @ about 4 watts dk. Thanks guys - Rumrunner

 

[freecell]

the heater (cathode) supply voltage will have to be increased to 31V AC or DC and be able to deliver at least 450ma. of current to all of the 31LQ6s' cathode elements for optimal operation.

25LQ6/31LQ6

 

[rumrunner]

Thunderbolt 305

the heater (cathode) supply voltage will have to be increased to 31V AC or DC and be able to deliver at least 450ma. of current to all of the 31LQ6s' cathode elements for optimal operation.

I guess you didn't read my entire post, Freecell. I series-strung the filaments (4 tubes @ 31 volts per =124 volts). These are supplied from the mains WITH a 3 amp separate fuse and a new switch for filament - only warm ups (or extended idling with no stress on HV transformers, diode bridge, or filter caps. If I had not increased the fil voltage from 6 volts there would be virtually no outpoot! The amp is up and making power, just lower than normal and with a hum in received audio. Filament voltage is about 30.4 volts - quite adequate.

 

[freecell]

"4 tubes @ 31 volts per =124 volts"

lol. got it.