Re: tube-noob question

Ross, NS7F wrote:
In a circuit with two 6.3V tubes, can I just series the filaments so
that I can use a 12-13.8V supply? Or are there subtleties that I'm
missing?
Thanks,
Ross NS7F

I'm an almost tube newbie, but here's what I know of this, in order of importance:

* the tubes have to draw the same current, else one tube will get too hot and the other will run cold.

* some tubes take longer to warm up than others. When they started putting color TV's together with long strings of filaments that added up to 110V, they also instituted "controlled warm-up" filaments so they'd all warm up in about the same amount of time. I don't know if this is such a big deal at 12V.

* If you're doing really low-level audio (or a VFO for that matter), the filament can "talk" to the cathode a little bit. Running your 6V tubes from a winding with a center tap will minimize this. Running the filament slightly positive (I think) to the cathode will suppress issues of the filament emitting electrons that bias the cathode. Building your circuits so the cathode goes to a hard ground will significantly minimize these effects, at the cost of quite a bit of circuit convenience, although you see it done.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
.

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