Is there any down side to using a larger sized regulator chip? I need 1.2 amps for the heaters I'm planning to feed, which seems a bit close to the 1.5 amp limitation of the LT1086. Is it OK to use the 3 amp LT1085? I don't know if that means a larger heat sink requirement, or what, but I'll bet that somebody here does. Thanks!
Heater Inrush
Seems I recall that vacuum tube filaments have very large inrush currents, so make sure the regulator you use is safely current limited. With current limiting heaters will take longer to stabilize but tube life will possibly improve.
Tube fans; someone verify my recollection of filament inrush current at 10 to 1?
Seems I recall that vacuum tube filaments have very large inrush currents, so make sure the regulator you use is safely current limited. With current limiting heaters will take longer to stabilize but tube life will possibly improve.
Tube fans; someone verify my recollection of filament inrush current at 10 to 1?
Dr. Ruth said that size doesn't matter 
but you probably aren't old enough to remember that. I think that Helen Gurley Brown had a different opinon.
Don't forget that the regulator has its own "overhead" -- some voltage which is going to get chewed and spewed out as heat -- depends upon whether it's low dropout regulator, or the garden variety 7812 etc.
Have you considered just using a beefed up zener (i.e. a zener on the base of the transistor and a little bias current) -- there really is no need for "regulation" per se since the load on the tube filament is invariant.
but you probably aren't old enough to remember that. I think that Helen Gurley Brown had a different opinon.Don't forget that the regulator has its own "overhead" -- some voltage which is going to get chewed and spewed out as heat -- depends upon whether it's low dropout regulator, or the garden variety 7812 etc.
Have you considered just using a beefed up zener (i.e. a zener on the base of the transistor and a little bias current) -- there really is no need for "regulation" per se since the load on the tube filament is invariant.
An optional Plan B,
Allen Wright in his Tube Preamp CookBook recommends using separate LM317 as CURRENT regulator for each tube heater. A small, device mounted, heatsink will then suffice. No switch on surge to worry about. Having said that, I don't remember when I last changed a tube because the heater had gone open circuit so I don't believe switch on surge is a major problem for tube heaters. Don't worry about power tubes - just run them from the 6.3V AC.
Cheers,
Ian
Allen Wright in his Tube Preamp CookBook recommends using separate LM317 as CURRENT regulator for each tube heater. A small, device mounted, heatsink will then suffice. No switch on surge to worry about. Having said that, I don't remember when I last changed a tube because the heater had gone open circuit so I don't believe switch on surge is a major problem for tube heaters. Don't worry about power tubes - just run them from the 6.3V AC.
Cheers,
Ian
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