Heater Voltage

[cannikin]

Heres an easy one for you Tube Gurus:

My heater voltage is too high about 7.1Vac - which is making the 6973 (x2) and 12AX7 (x3) extremely hot (I could burn an egg on these tubes).

They are suppose to the standard 6.3V

What is the best way to get them to the correct Voltage.

Thanks

 

[analag]

Add some series resistance in the heater circuit. Go to RadioShack and get some 1 ohm wire wound resistors.

 

[ioaudio]

6973 (x2) and 12AX7 (x3) 0,45 + 0,45 + 0,3 + 0,3 + 0,3 =1,8 ampere heater current. so you´d need a 0,444 R resistor.

 

[analag]

So you parallel two 1 ohm for increased wattage and there you go. That's close enough.

 

[clintrubber]

IIRIC a Philips tube databook mentioned a recommended tol. on the heater-voltage of 10%. Not too high, but also not too low.

 

[CJ]

You could rectify that, then 7806 with a juicy pass transistor.

That way you get low hum And long tube life.
But much more hassle.

What kind oif xfmr? Thats not very close to 6.3.
Must be meant for lower pri voltage.