How to measure heater voltage

Chris Adams · « **on:** 25 May 2013, 01:19 pm »

I've done a search on the web and AC but can't find the info I'm looking for. I have an Audio Research LS-1 and I want to measure the heater voltage for the 6DJ8 tube. I know it needs 6.3 volts and that the heater is pin 4 and 5. What I don't know is what to set the multimeter on (AC or DC volts) and where to place the + and - probes. Any help would be appreciated. Thanks!

Maritan · « **Reply #1 on:** 25 May 2013, 02:43 pm »

This piece of advice comes with all the usual caveats - at your own risk. You could hurt or kill yourself if you touch the wrong thing. I'm not liable for any damages to amp or your person etc.

Sucks I even have to say the above.

Anyway, you'll set the multimeter to DC. The probes will be placed on 4 and 5. Honestly doesn't matter which way. If you connect them one way, you'll get a positive reading. If you connect them the other way, you'll get a negative reading. Either way, if you just take the numerical value, you'll have your answer.

Good luck.

Chris Adams · « **Reply #2 on:** 25 May 2013, 04:35 pm »

Maritan, Thanks so much. I was reasonably sure that this was the way to do it and you have confirmed it for me.

FullRangeMan · « **Reply #3 on:** 25 May 2013, 10:23 pm »

Would be safe use rubber gloves to do this measurement, dont use rings or watches and dont do it alone.
If anything goes wrong a properly instructed adult person would save you.
In the 70 years I was save by my grandmother from a condenser.

Ericus Rex · « **Reply #4 on:** 26 May 2013, 12:43 am »

If you get a real funny reading try putting the black lead to ground and touch the red lead to either pin and see if you get something closer to 6.3V.

Maritan · « **Reply #5 on:** 26 May 2013, 02:28 am »

Good point made by Ericus Rex. I read too quickly and assumed that one of the pins you mentioned was ground.

If both 4 and 5 are heater pins, you will most likely have to find ground and measure the voltage between the heater pin(s) and ground.

Chris Adams · « **Reply #6 on:** 26 May 2013, 02:51 am »

Quote from: Maritan on 26 May 2013, 02:28 am

Good point made by Ericus Rex. I read too quickly and assumed that one of the pins you mentioned was ground.

If both 4 and 5 are heater pins, you will most likely have to find ground and measure the voltage between the heater pin(s) and ground.

Now that's interesting. I read on another forum to measure between pin 4 and 5. In fact the person asking measured from pin 4 or 5 to ground and said he blew a fuse. Because I wasn't there, I have no idea of his skills and he said he was a novice, so how he blew the fuse I'm not sure.

I did measure across pin 4 and 5 and got a reading of 5.84V. I know that's a tad low but from what I've read, 5.5 to 6.3 is kosher. Hmm, I may go back and check between the pins and ground to see what I get.

Thanks for the help.

Chris Adams · « **Reply #7 on:** 26 May 2013, 02:40 pm »

If anyone is interested, I did some more searching; many diagrams and instructions say the voltage across pins 4 and 5. I also checked the circuit by sight and with multimeter and pin 4 goes directly to the voltage regulator and pin 5 goes to ground through three parallel resistors that allow for adjustment of voltage to the heater. The resistors measure 24.3 ohms; calculating the resistance of the three, it comes to 24.268 ohms with zero tolerance, so I'm well within spec.

The reason for all of this is that I bought a pair of 6DJ8 Amperex Bugle Boys and one died after about 40 hours. The fellow I purchased them from asked me to check the heater voltage.

Thanks for all of your help without which I think this would have taken me much longer.