Heater voltage to high

[danotron]

I'm mod'ing a Champ 600 and I just noticed the heaters are running at 8V. How do I lower the voltage to 6.3? Will 8V kill the tubes real fast? Will heater voltage affect tone?

[jjman]

Not good. Good ac meter? Resistor(s) can be used to drop the volts. Just need the total heater current draw and ohms law to get to the value.

Ohms=1.7v / 0.75amps= 2.26ohms. So 1ohm in each line should work.

Watts=.85v x 0.75amps=.64watts ea resistor. So 2 or 3watt pieces should be more than adequate.

But this shouldn't be the case with 8vac. I wonder if they are all like that? You have the circuit running normally when measuring or is it in a "standby" mode from modding?

[Andy Le Blanc]

You can put a 20 to 50 ohm ww pot. in series before the heaters and dial in
the voltage you want. You might have accidentally lifted a artificial center tap.
Its the two 100 to 47 ohm resistors going to ground if the amp has them .

The danger is that running the heater at 120 to 200 % of the recommended
voltage will reduce the cathode coating. It evaporates into
the tube vacuum and recollects on the internal parts of the tube, sublimation.
This reduces the cathode ability to provide the electrons that make the tube go,
and sets up the condition for interelectrode leakage. You will eventually
deactivate cathode and screw up the tubes characteristics.

[tubeswell]

You can use 2 x 6A diodes back-to-back in series with each side of the winding. This should drop the voltage by 1.2VAC, which will get you to 6.8, which should be able to work (although that is still highish, it is better than 2CW

[dartanion]

Did you measure with tubes in or out of the amp. If they were out, you can expect the voltage to be high since there is no load on the PT.

[danotron]

measured with tubes in cct. Everything sounds as it should just those heaters are a tad high.....I think I will drop them with a resistors as jjman suggests

thanks guys

[mcrracer]

What is your AC voltage at the wall outlet?

[Structo]

Hey check out what the Valve Wizard has to say about heater voltages.
You can use a couple diodes to drop some volts.
Also some other alternatives to get you going, because eventually the tubes will give up if the voltage is too high.

Look at Voltage considerations:

http://www.freewebs.com/valvewizard/heater.html

[danotron]

Checked my house Ac and it is 132VAC....I double checked that, then triple....it is 132VAC...

Thanks for the valve wizard link......I will give it a read....

[tictac]

132VAC Wow, that's way too high. You need to get an electrician to your house pronto or you'll have more problems than high heater voltage. 132V is the upper safety limit for electrical appliances in the U.S.

TT

[Andy Le Blanc]

They're pushing current, Its in response to every one trying to reduce
the electric bill. There's nothing you'll be able to do. Design around the voltage.

My power supplier is CMP, they got bought out by FLP, which is a subsidiary
of a large corporate entity owned by another group in Spain.

The math works out significantly in the power companies favor at the higher voltage.
You'd better start running around your house with a meter and measure
the resistance of the PS in all the electronic consumer products you have.

THROW AWAY ANYTHING WITH A RESISTANCE OF LESS THAN 1K.

I used to have a LED clock that cost 56$ a year just to leave plugged in.

[dartanion]

You can use a variac or a power regulator/conditioner. I have seen my wall voltage vary around 5-7 volts in both directions. Nothing over 130VAC though.

[stoo]

I've never tried this but....How about using a bucking transformer arrangement?
About 1/2 way down here...
http://www.mylespaul.com/forums/squawk- ... ac30s.html
Stew

[Bob Reinhardt]

id suggest a variac. you can dial it in for days when the voltage changes, my house varies from 118 to about 128, so i use a variac to bring things down to 120 for testing/measuring for consistency.

[Allynmey]

I use a variac on my bench...always. I ask the customer the wall voltage at his studio/home etc. and set it there when I bias/tube. Of course this doesn't mean shit once he starts gigging with it....