• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Heater voltages

Rod Coleman

Member
2004-07-25 6:55 pm
UK
6.2V is no problem, especially with small-signal valves.

6.5V is within specification, and is OK, but for long-time running, or if the valve is not easy to replace (eg some lovely old OSRAM rarity) it is worth avoiding overvoltage. 6.15 to 6.25V is worth aiming for. Even a few percent extra will reduce the cathode's lifetime, since it's running hotter.

If it were mine, I'd add 100-ohm resistor [1W] across the heater with 6.5V on it.
 

Rod Coleman

Member
2004-07-25 6:55 pm
UK
Nuuk, I was only guessing!

If you find that 1,2K works, then that is fine. Forcing it down a little more may be worthwhile.. perhaps 6.2V would be a perfect perfect solution.

Maybe, you will find that the sound improves, somewhere between 6.05V to 6.25V - could be worth experimenting!
 
Thanks Rod.

I always measure stuff before closing the case but wondered if you had perhaps used a calculator and got the decimal point in the wrong place.

Not being pedantic but in another situation hazarding a guess for somebody less experienced in DIY could spell disaster. Better just to say something like try some resistance across the heater with the higher voltage. ;)
 
Another solution to too high a heater voltage is to "adjust" the voltage by putting a pilot light either in series or parallel whichever is more appropriate for the application. The bulbs come in a variety of voltages and currents so you can adjust the voltage by changing the type of bulb.