12v heaters in series question

[mountianjustice]

Is it OK to run  three 12ba6 tube heaters in series from an 18vdc power supply ?as in into pin 3 on tube 1 and out of pin 4 into pin 3 of tube 2 out of pin 4 on tube 2 into pin 3 of tube 3 pin 4 of tube 3 to ground

[Transmogrifox]

It looks like the 12ba6 uses 12.6V heaters.  Putting 3 in series would leave your heaters too cool.

If you were using 6ba6 (6V3 heaters) then I would say 18V is close enough.

Here's a simple boost converter that you can use to get the 37 volts you need from an 18V supply, just change the zener stackup to about 36-ish to 38 volts and change the inductor to 100 uH to improve efficiency (lower frequency):


You can also get an HV plate voltage by making the schematic as shown and tweak zeners to whatever HV you need.

[PRR]

> three 12ba6 tube heaters in series from an 18vdc

Not all "12xxx" tubes have dual-connection 12V/6V heaters. In fact very few do, except our favorite 12AX7 12AT7 12AU7 series.

xxBA6 is a pentode on a 7-pin base. Pentode has 5 electrodes. Heater has 2 ends. So all 7 pins are in-use. No spare pin for a heater mid-point tap. (Yes, some pentodes only bring out 4 electrode connections, but the ccBA6 gives you all of them for special tricks.)

As said, 6BA6 is your dog. One of the most-popular tubes of all time. Stocks still available around $8 each.

I'm having a hard time picturing what audio amplifier needs three xxAB6 in one box. That's a LOT of gain. We only needed two similar tubes to pull WABC-AM out of thin air in the far fringes of New Jersey.

[mountianjustice]

This is what ive got going on guys.
http://i1381.photobucket.com/albums/ah234/mountianjustice/TRIPPLE%20BA6TARD_zpsad0desox.jpg

[mac]

Long ago I connected two el84 heaters to a 12v supply, and I noticed that for a second or two one filament went too bright while the other was cold, less resistive.
Small resistance differences made one tube take more than 6v for just a moment.
I changed tubes and I had the same result.
I'm not a tube expert, so I can't tell if doing it many times can hurt the heaters.

mac

[PRR]

> This is what ive got going on guys.

Those heaters are NOT in series.

You are putting 18 Volts on 12 Volt heaters.

If the tube heater lasted 10,000 hours (not atypical) on rated voltage, at 1.5X rated voltage the tube life will be about 51 hours before heater failure.

So yeah "it will work". Depending how much you love it and use (or power) it, days or months.

I won't even go into how you can get an audible noise in a loud-speaker fed through 320K (a 40,000:1 mis-match).

Especially when the loudspeaker is *shorting* the last 12BA6 of all its plate current. (You surely expected to put the speaker *after* the 0.01u coupling capacitor.)

[mountianjustice]

I see now that the heaters are not in series  your right i guess they are running parallel @18vdc. Wow wonder it even works or worked as long as it has. And i need to also change that speaker to an output jack on the schematic the unit feeds a power amp not a speaker my bad on that one.

[mountianjustice]

I think the thing to do is just run the heaters on a T7812ct regulator and be done with it.

[PRR]

> wonder it even works or worked as long as it has

That 10,000 hour estimate was just a goal. To reliably beat 10,000 hours in 24/7 military and industrial use, the design really had to aim past 100,000 hours. If all goes well, at rated voltage, you may not live to see the heater fail.

The longest I have seen was a tube put in service in the mid-1930s, run 24/7 until the late 1950s, when it was replaced for low emission (not heater failure). Someone computed a quarter-million hours.

If you over-volt 1-1/2 times, a "250,000" hour tube is more like 600 Hours, which is like 2 years at 2 hours a day, a LONG time for a guitarist.

I do think getting down nearer 12V is wise.