how to wire 6.3VDC heater on a heater with center tap (12.6V series, 6.3V parallel)?

[jarthel]

please have a look at the block diagram of the connection: http://img515.imageshack.us/my.php?i...titled1ka9.png

Is this the correct way of using a 6.3VDC (voltage regulator) supply on a tube heater with center tap?

Would the connection be the same if the voltage source is current regulator using an LM317? something like this: http://www.tubecad.com/july2000/img21.gif

Thank you very much

[DigitalJunkie]

Yep,that looks correct to me.

Each "half" of the 12A_7 filament is 6.3V.
In series = 12.6V @150ma
In parallel = 6.3V @ 300ma.

[Salas]

Originally posted by jarthel
please have a look at the block diagram of the connection: http://img515.imageshack.us/my.php?i...titled1ka9.png

Is this the correct way of using a 6.3VDC (voltage regulator) supply on a tube heater with center tap?

Would the connection be the same if the voltage source is current regulator using an LM317? something like this: http://www.tubecad.com/july2000/img21.gif

Thank you very much

-You are correct on your schematic.
-If you opt for current sourcing, know that its going to take 40 seconds to see the heaters glow well. If you do it in some preamp be sure to wait as much before you turn on your power amp to avoid a thump. CS is good on not shocking the heater and beneficial for the long life of those NOS. It does sound softer, less hazy, and more bouncy too.
I don't know about cathode stripping though, prolonged exposure of non emitting cathodes to high voltage plates does occur (but inverse progressively so), since the heater comes up so slowly with CS, that even a tube rectifier is well up and running by then. My tubes are still healthy but its only about 4yrs I use CS in my non power level circuits so to know better.

[ray_moth]

Current regulation of the heater supply is OK, provided that there is only one tube heater or, if there are several tube heaters, they are in series.

[arold19]

If I have only 6.3V transformer, it is possible to drive 12A_7 heater???? They need 12.6 V...
Can I but the negative point of the 6.3v on the center tap of the heaters, and the positive ont the two heater??
And the sound will be the same of less good??

Thank you !!!

[jane]

Originally posted by ray_moth
Current regulation of the heater supply is OK, provided that there is only one tube heater or, if there are several tube heaters, they are in series.

Strictly speaking: 12A_7 wired for 6.3V/300mA are two heaters in parallel. Is it a good or a bad thing to current source a 6.3V 12A_7?

Jan.

[Dave Cigna]

Originally posted by jane
Strictly speaking: 12A_7 wired for 6.3V/300mA are two heaters in parallel. Is it a good or a bad thing to current source a 6.3V 12A_7?

Are you thinking about heaters that are not exactly matched? If so, my first thought is that it doesn't matter whether series or parallel, constant voltage or constant current. In any case the imbalance in heater powers will be equal to the imbalance in the heater resistances. Which uses more power depends on how things are hooked up, but the ratio of the heater powers will always equal the ratio (or inverse ratio) of the resistances.

Okay, but now consider the fact that the heater resistance goes down as it heats up. Higher temperature means lower resistance. Higher power means higher temperature, so higher power means lower resistance.

Let's try to use that fact to our advantage. Let's look for ways to heat them that have the one with higher nominal resistance using more power than the one with lower nominal resistance. That will push their operating resistances closer together. That circuit (should it exist) is self-balancing to some degree.

First of all, I don't see any difference between regulating the voltage or current. Fixing one makes the other variable, but they always settle at something equal to or near the nominal value.

So that leaves the question of series vs. parallel. With parallel wiring they both have the same voltage across them. P=V^2/R, so the one with greater resistance will use less power. That's the opposite of what we want. That doesn't balance the heaters, that increases any imbalance.

With a series connection the current through both heaters will be the same. P=I^2*R, so the one with greater resistance uses more power. That is what we want.

Of course, all of this is probably just academic; the real-world difference in heaters (and the consequences) might be small compared to the practicalities of building an amp.

-- Dave

[Salas]

If you current source with the LM317 in the end, maybe the 1.25/Ih type for the Ih setting resistor must be modified to 1.22/Ih so to contain resistor's value trip up when at work and hot. Keep that in mind if with the 1.25/Ih formula your measured voltage on the heaters ends up lower than expected. Depends on various stuff, but keep this in mind just in case.

[mr2racer]

How do you wire 12.6 volt heaters with 6.3 volts AC?

[DF96]

Originally Posted by Dave Cigna

Okay, but now consider the fact that the heater resistance goes down as it heats up. Higher temperature means lower resistance.

No, other way round. This means that best stability comes from voltage driving of heaters in parallel. Some valves were designed for series heating (for TV and AC/DC radio sets) and these may have heaters which heat up at exactly the same rate. Any valve designed for series heating can also be used for parallel heating. Valves designed for parallel heating can be used in series from a current source. Valves designed for parallel heating can be used in series from a voltage source, provided the series string is not too long.