Heater Voltage

[MBD115]

What should the heater voltage be and what is the best way to measure it? Just meter from pin9 or pin5 to ground with my meter set to AC mode, or meter from pin to pin, not to ground?

I'm not getting anywhere near 6.3VAC. Is this indicating a problem?

Thanks

[Cygnus X1]

Assuming a 12AX7, one probe to pins 4/5 (they are tied together), the other to pin 9 should give 12.6 VAC or DC depending on the amp design.

Power tubes 6V6, 6L6, KT66, KT88, EL34, 6550, 5881 it will be 6.3V on heater pins 2 and 7.

[MBD115]

Found out my meter has gone bad. Changed it out and am now getting closer reading I think.

12AX7 - from pin5 to pin9 = 6.8VAC
6L6 = that same 6.8VAC reading

I'm going to buy a new meter.

Thanks

[Jana]

probing from pins 4/5 to pin 9 should be 6.3vac, not 12.6 vac. 6.8 vac is within tolerances of +-10%, and is about what one would expect if this is a reading with the tubes pulled.

[MBD115]

My new meter is reading 6.78VAC on all of the tubes. This is with the amp warmed up a little and with all the tubes in.

Am I supposed to remove the tubes?

Thanks for the help.

[jjman]

All 5 of my amps run around 6.7vac on the heaters with the tubes in.

[MBD115]

Thanks everybody for your help!!!!!

[Cygnus X1]

probing from pins 4/5 to pin 9 should be 6.3vac, not 12.6 vac. 6.8 vac is within tolerances of +-10%, and is about what one would expect if this is a reading with the tubes pulled.

d'oh.

One of those things I guess.
I'm going back in my cave.

Thank you Jana.

[fishy]

Am I supposed to remove the tubes?

It makes a difference if the tubes are in. The reading will generally be lower due to the transformer load if the tubes are in. Without the tubes in, the voltage will usually be higher due to no load being put on the winding.

[breakfastbuddy]

if only pin 4-5 is conected its 12,6 , if 4and 5 is tied together and 9 is connected its 6,3 when you measure from 9 to 4and 5 and the tolerance is 10%

[Phil_S]

At 6.8v you are about 8% over 6.3v. I wouldn't be surprised at all if your line voltage is around 124v = 115 + 8%. There is a direct relationship.

[gearhead]

if only pin 4-5 is conected its 12,6 , if 4and 5 is tied together and 9 is connected its 6,3 when you measure from 9 to 4and 5 and the tolerance is 10%

Wouldn't you need a different transformer with a 12.6V heater supply to run the preamp heaters in series (pins 4 and 5 only)?

.

[benoit]

if only pin 4-5 is conected its 12,6 , if 4and 5 is tied together and 9 is connected its 6,3 when you measure from 9 to 4and 5 and the tolerance is 10%

Wouldn't you need a different transformer with a 12.6V heater supply to run the preamp heaters in series (pins 4 and 5 only)?

.

Yep.

[MBD115]

At 6.8v you are about 8% over 6.3v. I wouldn't be surprised at all if your line voltage is around 124v = 115 + 8%. There is a direct relationship.

It is!!!!