Chuck Guzis wrote:
Can't get
much cheaper than effectively free for a well regulated,
high current DC power supply using a modified PC power supply that
isn't otherwise being used. Plus, the idea of using tubes with 5V
filaments instead of 6.3/12.6V reduces the competition with typical
audio tube customers and makes the use of a high-current 5VDC
supply possible.
For digital circuits (I assume that's what we're
still discussing), why is a DC heater supply necessary?
Because I don't want to hear 60Hz hum when I plug my headphones into the flip-flop
output. ;-) Seriously, you are absolutely correct that AC could be used for the filaments
in this case, but the PC power supply is being built for multiple uses and will just
happen to be there for these tube logic experiments. I planned to mod the PC power supply
well before coming up with this low voltage tube logic project (which may or may not
succeed). My goal is also to provide a commonly available, cheap and multi-use power
source for the tubes that could be duplicated by others if I succeed in this and decide to
put the tube logic project on a web page. Like me, rather than just building a supply
that would be used only with the tube project, they would be building a very cheap,
high-current DC power supply useful for other purposes.
If you do decide to use a regulated DC supply with
overcurrent protection, keep in mind that cold heater inrush current
can be substantially greater than the nominal heater current
rating.
Right now, my goal is to build just an astable multivibrator clocking a 4-bit counter. To
show the alternating state of the multivibrator, I'll light the tube from below
through the hole in the center of the socket with a two-color LED and the states of the
counter tubes will be indicated by lighting them from below with a red or blue LED.
I've got the special effects visualized, but that's the really easy part.