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Re: Vacuum Tubes
Original Poster: "Stephen G. Stanton" <ulflyer-at-i-cafe-dot-net>
Ben: I would reconsider using the 304s for your coil unless you can get
them free. Sockets for them are getting very hard to come by. Also, each
tube requires 10 v at 12 A to light it up (you could wire each one in
parallel but that would require 5 v at 25 A, a huge transformer!!.
SNIP
Hi Stephan,
Uh, I donīt quite get the above comment. Are you trying to suggest that if you
wire your tube filaments in parallel, you would need:
Total Volts Needed=Volts per tube/Number of tubes ?
Nope!!
Most tube radios from the late 40īs-late 60īs use 6.3v per filament and all
filaments are wires in parallel. There are a few exceptions where the
filaments are wired in series (to eliminate the need for a filament
transformer).
Using your logic I would need (for a SABA with 14 tubes, all wired in
parallel, roughly 6.3v/250mA per tube) a transformer with 0.45V and 3.5 amps.
Electron emission would be zero. A 6.3V 3.5A xformer would be the right one,
tho.
For the 2 x 304 tube setup you would need a transformer with either:
a.) Parallel filaments: 10V and 24A (V=Vtube // I=2 x ITube)
or
b.) Series filaments: 20V and 12A (V=2 x Vtube // I=ITube)
RTotalSeries = R1+R2+..... etc.
1/Rparallel = (1/R1)+(1/R2)+.....etc.
Plugging this into ohms law (V=R/I) lets you see why your logic doesnīt work.
If you connect two tube filaments in parallel and use only one half the
voltage and twice the amps (needed) each filament only sees one half the
voltage and one half the xformer current.
(i.e 5V and 25A: each tube 5V and 12.5A. Of course the tube wonīt pull the
12.5A because your are only giving it 5V instead of the rated 10v)
Tube greets from germany,
Reinhard