Philco Seventeener II

[bandersen]

Keep in mind the fusistor is only on the B+, not the tube filament string. I'd guestimate something around 200-300 mA of current.

Also the reason for the resistor is that the old rectifiers can't take the surge current. Modern are more robust especially if you go with 1N5408s. The resistor value isn't critical.

I also suggest adding another fuse to protect the whole set.

[Crist Rigott]

Originally Posted by bandersen

Keep in mind the fusistor is only on the B+, not the tube filament string. I'd guestimate something around 200-300 mA of current.

Also the reason for the resistor is that the old rectifiers can't take the surge current. Modern are more robust especially if you go with 1N5408s. The resistor value isn't critical.

I also suggest adding another fuse to protect the whole set.

Bob,
Thanks for the quick reply. The TV is rated at 150W or 1.3A. Less the 600ma filament string gives me .7A through the Fusistor. If I'm reading your reply correct, I really don't need a Fusistor, just a fuse upstream of the filament tap off....right? I could easily relocate the filament tap off to the downstream side of a fuse.

[jr_tech]

I used an 8ohm 5 Watt resistor, to give a bit of extra surge protection with today's higher line voltages. I also added a fuse IIRC, 2 amp slow blow.

200 volt rating for the 82 uuf cap should be fine, as the 150 k resistor and the 2 33 k resistors in series form a voltage divider network. The total resistance of the divider is 216 k (150+33+33).... 66k out of 216 k is about 30% .... 30% of 265 volts is about 80 volts. When the tube warms up and starts drawing current, the voltage at that point drops about 10 volts more to 70 volts.

jr

[Notimetolooz]

Originally Posted by jr_tech

200 volt rating for the 82 uuf cap should be fine, as the 150 k resistor and the 2 33 k resistors in series form a voltage divider network. The total resistance of the divider is 216 k (150+33+33).... 66k out of 216 k is about 30% .... 30% of 265 volts is about 80 volts. When the tube warms up and starts drawing current, the voltage at that point drops about 10 volts more to 70 volts.

jr

Jr is right about the voltage across the 82 pf increasing every time the set starts up from cold because the tube isn't drawing current. This does point out however that when something is designed that it is difficult to cover all the bases. If the 33K resistors in K4 increase a lot in value or open up then the voltage will be higher. This could also happen if in troubleshooting someone disconnects K4. Its hard to foresee every possibility.

[Crist Rigott]

Originally Posted by Notimetolooz

Jr is right about the voltage across the 82 pf increasing every time the set starts up from cold because the tube isn't drawing current. This does point out however that when something is designed that it is difficult to cover all the bases. If the 33K resistors in K4 increase a lot in value or open up then the voltage will be higher. This could also happen if in troubleshooting someone disconnects K4. Its hard to foresee every possibility.

I have a 200v cap coming. On the other hand, I can always order a 82pf 1KV SMD that will fit the through hole pads well enough. Maybe I should hust go with one of those?

[Crist Rigott]

I'm done with the design of the Couplets. If you get a chance would you mind going over them to see if I have them correct?

Thanks.