On Thu, 25 Dec 2008 11:03:48 -0500, ken scharf wrote:

Tim Wescott wrote:
Bill M wrote:
I'm a little confused again.

Setting up a 1624 tube for cathode biasing and also need to create a
center tap for keying to ground.

The book says 610 ohms at my voltage. So would I use a pair of 1200
ohm resistors in this case?

My logic is since there is not a separate cathode then the two R in
parallel would raise the filament 'cathode' 600 ohms above B-minus.

TIA and Merry Christmas,

Bill

(Disclaimer -- I haven't done this. It's just knowledge gotten from
lots of books, and lots of solid-state circuit design experience).

No, because all the filament voltage will go to mildly heating up the
resistors, and none will go to wildly heating up the filament.

Use a center-tapped filament transformer, and put the 600 ohm resistor
between its center tap and ground. If necessary, use a separate
transformer just for the 1624s.

If his un-centertapped filament winding is ONLY supplying that one tube
and he has each leg going to ground through a 1200 ohm resistor that
would result in a 600 ohm connection to ground. So it should work.
Remember that's 2400 ohms across the filament, it won't suck up much
heater current at all.

Sorry. I was visualizing the 1200 ohms each in series with the
transformer, whose center tap is grounded.

Of course the alternate way makes perfect sense.

And here it is too late to ask Santa for more brains for Christmas.

--

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

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