You can either put this 100R-100R virtual CT behind the diodes or you opt for a trimpot instead that you adjust for hum minimum.
Best regards!
Best regards!
If you have a seperate transformer for the heaters you could also add a resistor on the primary side of the transformer.
Whatever the reason for higher than desired heater voltages, a resistor somewhere is a pretty good solution these days. Not, of course, to just waste half or some large amount of available power, but a reasonable solution to modern, considerably higher, mains voltages in North America, and probably elsewhere (motors like it better, everyone loves AC in modern Summers). Burning off 10%-ish of heater power is a real possibility for restoring Golden Age audio gear. If you're a mil-surp potted and welded iron fan like me, the 115VAC primaries issue isn't a new one. Dedicated Kenyon fans need to adapt to 110VAC.
The thermally ideal solution for all over-voltage issues with mil-surp or Golden Age gear would be a bucking transformer, which helps the B+ voltages too. But every case is different, and we're not familiar with your particular gig. Be particular!
All good fortune,
Chris
The thermally ideal solution for all over-voltage issues with mil-surp or Golden Age gear would be a bucking transformer, which helps the B+ voltages too. But every case is different, and we're not familiar with your particular gig. Be particular!
All good fortune,
Chris
My comment was simply due to your earlier posts, and how they were presented.
You sounded to me like a confused pre-teen, putzing around and worrying over 0.5 volts of filament voltage, and unsure about current ratings and series-parallel operation.
When I knew that tubes have a non-critical margin of operation.
No need to tell me about how many grids/plates in the tubes, trust me, I've been a qualified service technician for over 40 years, and now being almost 70, I was building tube amps when I was 15 in 1969.
I learned back then the fundamentals of tubes and electronics, and understood the Ohm's Laws, resistor Color Codes before that.
I hope that clarifies things.
Chris, The bucking transformer was the first thing I purchased. I thought I could squeeze it into the chassis...
I could, but would need to redesign a board that sits in a side area to fit the transformer. Then, I realized cross-talk might be something I have to worry about...
2 years ago when building the crossovers for the Elsinore speakers, I sent low voltage, 1khz through an inductor and hooked up headphones to the others and was
blown away with how clear the tone was depending on orientation. Since I have limited space in the chassis, did not want another box on the floor (I call it the wifey factor) chose the path im on now.
If nothing else, I sure have learned much, the biggest thing is I have barley scratched the surface !!!
I could, but would need to redesign a board that sits in a side area to fit the transformer. Then, I realized cross-talk might be something I have to worry about...
2 years ago when building the crossovers for the Elsinore speakers, I sent low voltage, 1khz through an inductor and hooked up headphones to the others and was
blown away with how clear the tone was depending on orientation. Since I have limited space in the chassis, did not want another box on the floor (I call it the wifey factor) chose the path im on now.
If nothing else, I sure have learned much, the biggest thing is I have barley scratched the surface !!!
I once accidentally applied 25 volts DC to a 12au7 heater.
It was bright but survived.
6.9VAC isn't a problem.
It was bright but survived.
6.9VAC isn't a problem.
Yes, tube heaters don't fail as rapidly as incandescent bulbs 😉 . Once I've had a similar encouter when I erroneously connected a PL519 heater to more than 80 Vac 🙄😵...
Anyway, tube manufacturers allowed for 5 % tolerance either in heater voltage (for parallel supply heaters) or in current (for series connected heaters).
Best regards!
Anyway, tube manufacturers allowed for 5 % tolerance either in heater voltage (for parallel supply heaters) or in current (for series connected heaters).
Best regards!
Tubes were, and hopefully still are, made with specific filament properties.
The current draw is held to tight tolerences AKA 3A, 150mA, etc.
Some tubes have what is called "controlled warmup" filaments, mainly for series-connected circuits like radios.
The current draw is held to tight tolerences AKA 3A, 150mA, etc.
Some tubes have what is called "controlled warmup" filaments, mainly for series-connected circuits like radios.
Had on hand 1ohm 1 watt resistors, 2 in parallel on each leg and boom, have 6.3 on one and 6.1/6.2 on the other.
Amp finally up, tested out great and sounds better than ever..
So glad to have it back!
Amp finally up, tested out great and sounds better than ever..
So glad to have it back!
JEDEC coded tubes with this feature usually have an A in their designator, see 6SN7GT vs. 6SN7GTA or 12AX7 vs. 12AX7A.
Best regards!