Heater voltages

Nuuk · 2nd December 2010, 01:10 PM

I've just been checking the voltages in my DIY valve buffer. I measure 6.2v on one valve heater, and 6.5v on the other (I'm using one side each of two valves). The two heaters are wired in series and I wondered if this is a 'normal' difference, or it something is amiss?

DF96 · 2nd December 2010, 02:20 PM

No problem. A few percent difference in heater resistance is of no consequence.

Rod Coleman · 2nd December 2010, 04:16 PM

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.

Nuuk · 2nd December 2010, 05:22 PM

Many thanks guys. I'll add the resistor to the one running hotter (5687).

Nuuk · 13th December 2010, 11:27 AM

Rod, did you mean 100R or 1K? 1K2 actually brings the voltage down to spot on 6.3v.

Rod Coleman · 13th December 2010, 11:45 AM

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!

Nuuk · 13th December 2010, 01:14 PM

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.

Rod Coleman · 13th December 2010, 01:18 PM

OK! I should have said that this was a guessed value.

But one should never build a heater circuit without measuring the voltage, right at the pins of the base. The lifetime of the valve is VERY dependent on getting this right.

Palustris · 13th December 2010, 03:06 PM

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.

Nuuk · 13th December 2010, 03:30 PM

Thanks again for the suggestions guys. It has all been taken on board.

2nd December 2010, 01:10 PM	#1
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Heater voltages I've just been checking the voltages in my DIY valve buffer. I measure 6.2v on one valve heater, and 6.5v on the other (I'm using one side each of two valves). The two heaters are wired in series and I wondered if this is a 'normal' difference, or it something is amiss? __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

2nd December 2010, 05:22 PM	#4
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Many thanks guys. I'll add the resistor to the one running hotter (5687). __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

13th December 2010, 11:27 AM	#5
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Rod, did you mean 100R or 1K? 1K2 actually brings the voltage down to spot on 6.3v. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

13th December 2010, 01:14 PM	#7
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

13th December 2010, 03:30 PM	#10
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Thanks again for the suggestions guys. It has all been taken on board. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

2nd December 2010, 02:20 PM	#2
DF96 diyAudio Member Join Date: May 2007	No problem. A few percent difference in heater resistance is of no consequence.

2nd December 2010, 04:16 PM	#3
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire 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.

13th December 2010, 11:45 AM	#6
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire 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!

13th December 2010, 01:18 PM	#8
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	OK! I should have said that this was a guessed value. But one should never build a heater circuit without measuring the voltage, right at the pins of the base. The lifetime of the valve is VERY dependent on getting this right.

13th December 2010, 03:06 PM	#9
Palustris diyAudio Member Join Date: Aug 2006 Location: Cape Cod	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.

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