Series heaters = small problem?

[Klimon]

Hi,

Putting the heaters of two 6ck4 (same brand, same construction) in series I get a difference of 0.5V between both tubes (when one gets 6.5V the other one gets 6V); the tubes are responsible for this (I switched them and voltages switched along).

-- Would the 0.5V variation in heater voltage cause a notable difference in output (one channel sounding louder than the other one, the amp is SE)?

-- Would it dramatically affect the lifespan of (the/both) tubes?

If the answer to both questions is "NO", I'll happily live with it as such; both voltages would still be in the recommended region of 6.3 +- 0.3V and I wouldn't need to spend money I don't have anyway.

As before and after; many thanks!!

Simon

[Gold_xyz]

The difference can not influential it depends on schematics.
(gain, nfb, etc. etc.)
but I suggest a resistor in parallel at tube with the most greater tension,
for balancing power disipation between heater.


Datasheet of 6ck4 (GE) say 6.3 +/- 10% @ 1.25A
http://frank.pocnet.net/sheets/093/6/6CK4.pdf

that means tube can supply from 5.4 to 6.93

[Klimon]

Hi mr. Gold,

Excellent idea, that should indeed solve everything!!!

Thanks a lot / Simon

[Gold_xyz]

for equalize the power of heaters tube

[Gold_xyz]

If the total current is 1.25A (from datasheet)
and Vsupply 12.5V

P1 = 1.25A * 6.5V = 8.1W
P2 = 1.25A * 6V = 7.5W
(as the light bulbs )

this is already amply accetable.

With a resistor of 100 Ohm (2W)

I = 1.28A
P1 = 7.73W with 6.32V
P2 = 7.83W with 6.15V

I suggest a resistor from 100 Ohm to 180 Ohm 2W in parallel at
tube with the most greater tension.

Also this is enough simply to verify with Pspice.

[Klimon]

You're right, yesterday I experimented with resistor values untill voltages were within 0.1v; 100ohms works well. I'm using a 1W resistor (that's what I've got on hand) though.

Thanks again!

Simon