On Thu, 03 Dec 1998 22:15:35 Scott Townley <nx7u@primenet.com> writes:
>
>Those with long memories will recall I was whining about insufficient
>filament voltage in my (2)3-500Z amp...
>Well, I solved that problem by biting the bullet and finding room on
>the RF
>deck for the xfmr. Now instead of a pair of 7' runs of #10 (which
>subsequent calculations showed was *not* sufficient!) I have a pair of
>3"
>runs. I was able to verify the xfmr using a bank of 6 1ohm 25W
>resistors
>to duplicate the load of a pair of 3-500z filaments.
>The amp is GG so there's an old B&W FC-30 (or could be FC-30A...don't
>know
>'cuz the stickerplate fell off). Right now I'm getting 0.18V drop
>across
>each choke...for a total of 0.36V. With a choke input of 5.00V
>(measured),
>that's 4.64V at the tubes, I'M STILL A LOSER. Darn!
>Well that drop seems awfully surprising for a choke supposedly rated
>at 30A
>service.
>So, here's the litany:
>1. Are there known issues like this with the B&W FC-30(A)?
There are no voltage drop problems that I am aware of; used and sold that
part for many years.
>2. Any known OE's (Operator Errors) which could lead to this drop
>across
>the choke?
True RMS meter ???
>3. ...each end of the choke has four terminals, apparently arranged
>in
>pairs. If you mount the choke "on its feet" (it has little tab feet
>on the
>bottom), the top two terminals are closer together than the left or
>right
>pair (in other words, the four terminals form a rectangle that's
>longer
>vertically than horizontally). *Which pair is the "choke"???? Ohming
>it
>out won't tell me anything and I've never seen one in use!
OK, you have the right choke,
IN and OUT terminals are at opposite ends. Each individual choke pair of
leads are "in-line" but the old catalog here doesnt say which way ! You
have a choice of horizontal pair or vertical pair and a 50% chance of
being wrong the first time! There are no internal connections between
terminals or windings.
Take 10' of #10 wire and measure the voltage drop, that is the amount of
wire in each leg in the larger Radiokit 30A choke that works down to
160M. There should be somewhat less loss in the FC-30A. I never took a
B&W apart so not sure if they are using #10 or cutting it close with #12
You are only .1V low from the 5% low recommendation. In reality you
should set the voltage under full RF load. Reduce filament V until power
just starts to fall and then increase about .1V. That sets the ideal
point for that set of tubes. The actual voltage will vary depending on
tube condx.
73 Carl KM1H
>
>Thanks again to the planet,
>------------
>Scott Townley
>nx7u@primenet.com
>------------
>Collector of:
> Stoddard Aircraft EMI/RFI receivers and accessories
> Big Parts for that Big Linear Amp
> 70's era RF test equipment HP/GR/Tek
> Radio-related technical reference material 1940+
> ...anything else that will keep me off the streets at night
>
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>
>
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