dropping heater voltage

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ganzonimx
Hey get your own solder
Posts: 442
(3/31/04 11:16 am)
 dropping heater voltage
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 I like to ask to not mess up:

I'm working on a Bass amp with six 6L6 and 3 12A?7 tubes, makes up for a heater current of

6 x 0.9 A 3 x 0.3 A = 6.3 A

The heaters are at 7.3V. I like to reduce the voltage a little.

If I use 0.1 ohm resistor, that would drop the voltage by

0.1 ohm x 6.3 A = 0.63 V

the dissipation would bee 0.63V x 6.3 A = 4 W

Would that be OK to use a 0.1ohm/10W resistor?

Cris
 
Tiny Daddy
I will work on all amps
Posts: 580
(3/31/04 8:58 pm)
 Re: dropping heater voltage
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 You could use a resistor, or a diode or two.
 
6G6
Junior tube assistant
Posts: 150
(4/1/04 8:23 am)
 Re: dropping heater voltage
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 Cris,
Is that 7.3V with the tubes in or without a load?
If it's without a load, the voltage will come down some when you have the tubes in.
 
ganzonimx
Hey get your own solder
Posts: 447
(4/1/04 10:38 am)
 Re: dropping heater voltage
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 7.3VAC is with tubes in, I have 130VAC from the wall.

I also thought about lowering the voltage from the wall with a 6V ore 12V PT, but as it is a bass amp, I prefere to keep the little higher volatge on the plates.

How should I use the diodes?

Cris
 
Tiny Daddy
I will work on all amps
Posts: 581
(4/1/04 1:38 pm)
 Re: dropping heater voltage
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 Since it's AC, put 2 diodes in parallel and then in series with the filaments and they will drop around 0.7 Volts.

Edit: The diodes need to be paralleled but connect the anodes to the other's cathode.

Edited by: Tiny Daddy at: 4/1/04 1:40 pm
 
ganzonimx
Hey get your own solder
Posts: 451
(4/1/04 1:44 pm)
 Re: dropping heater voltage
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 THX T-Dady, I'll try that later today!

Edit: I used some old diodes I had laying around, they drop 0.9V, now the heaters are 6.3V

Cris

Edited by: ganzonimx at: 4/1/04 6:15 pm
 
Tiny Daddy
I will work on all amps
Posts: 584
(4/1/04 7:25 pm)
 Re: dropping heater voltage
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 Make sure the diodes are rated for 6 Amps or more. Each diode is conducting only half of the time so 6 Amps gives some safety margin.
 
 
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