Using a Zener Diode to Regulate Heaters?

[Mooreamps]

Beautiful! Thanks, Merlin!

Will I gain hum if my heaters are uneven? i.e. if one side is at 3.5VAC and the other 2.8, won't they not quite cancel/humbuck?

Yes they could on the pre-amp filaments, in theory, because they are center tapped internally. PA filaments are not center tapped.

I suppose I could cobble up some kind of a diode based clipper circuit that would clip the top of the sine wave above some value, like 6.5 vac. But my preference is still leaning toward dc for pre-amp filaments, in which case adding a linear regualtor would pretty much abate the problem.

-g

[Alexo]

Thanks, Gary.

I agree that regulation is clearly the best way to do it, here I could drop the .7 volts and it would work great in my house, but it may be below 6.3 if I go somewhere else, etc., but I just don't think I'll be able to find space in the 5 amps I want to upgrade to insert all those regulating circuits. I suppose if I used a 200 ohm "hum adjust" pot instead of the 2 100 ohm resistors or the transformer center tap, that might help a little.

About the internal humbucking - yeah, that would theoritcally be an issue, then again, I've used 6SN/L7's a lot and others use EF86's and it hasn't been an issue for most folks, so I think I'll just give the diode thing a shot and see how it plays out in the real world, I'm betting (hoping) it will be fine,

Then again maybe I should just get one of

these

[Mooreamps]

Thanks, Gary.

I suppose if I used a 200 ohm "hum adjust" pot instead of the 2 100 ohm resistors or the transformer center tap, that might help a little.



these

If you can't find a 200 ohm pot, the 100 ohm pots are more common and will work just as well. Just make sure the pot itself is rated for at least 1/2 watt, and I think you should be fine.

-g

[Alexo]

Thanks Gary, I appreciate the advice.

[Merlinb]

[quote="Alexo"]Thanks, Gary.

I agree that regulation is clearly the best way to do it, here I could drop the .7 volts and it would work great in my house, but it may be below 6.3 if I go somewhere else, etc.[quote]
You don't need to worry about that, you can run as low as 5V without any problems. You just don't want to run ABOVE 6.3V, unless you absolutely have to.

[sjfirebird]

If your house voltage is consistantly high, how about using a variac.

[Strat]

If you drop the voltage on one leg would it not be better to ignore the centre-tap on the PT wind and use the two 100R's and form one 'downstream' of the dropper (diodes or resistor).

[Alexo]

If your house voltage is consistantly high, how about using a variac.

That is by far the simplest solution. I need to get one of those anyway...

If you drop the voltage on one leg would it not be better to ignore the centre-tap on the PT wind and use the two 100R's and form one 'downstream' of the dropper (diodes or resistor).

I would think so but also that you wouldn't want to use 100 ohm resistors, I think you would want to accomodate your resistor values to the voltage difference between the two legs or use a pot. I know of a source for cheap linear 2 watt 200 ohm screwdriver-turned shaft pots, but I'm forbidden from mentioning it on this forum.

[Wannatone]

I suppose I could cobble up some kind of a diode based clipper circuit that would clip the top of the sine wave above some value, like 6.5 vac.

-g

Just think a little bit about it... The only thing limiting the current when clipping is active will be the heater winding resistance of your transformer plus your wiring and the internal diode resistance. You're more or less getting close to short-circuit operation when the circuit is clipping. Not good for your tranny, and it might even blow the mains fuse...
That's actually the main design fault of the initial schematic.

IMHO the whole thread appears not any helpful for a beginner who's trying to learn basic electronics.

If you follow that path, the next problem to fix will probably be the excessive anode voltage in your amp.

Why not just use a dropper tranny do get the wall voltage down by 6 or 12 volts. That way you'd get everything working properly inside your amp, and you wouldn't have to rip the whole crap out when you're moving the amp to a different place where the wall voltage is more 'normal'...
You could also use a variac of course.

Get the problem fixed at its source, not elsewhere... (given it's a problem at all when the heater voltage is still within the specification limits...)

[jem]

Sounds like one of those Furman or APC power conditioner/regulator would work. Bad side is $$ and another piece of equipment to lug around and protect.