On Behalf Of John Lyles
Sent: Sunday, March 21, 2010 8:43 AM
To: amps@contesting.com
Subject: [Amps] B&W 800 RF choke
I used one as a screen choke at 2800 KHz, in a 100 kW amplifier at work.
It was fine there, but not sure about 1900. This was 12 years ago. I
took data on a B&W 800 using a vector impedance meter and plotted it. If
I can find it tomorrow, will scan and ship it here.
## I'm looking forward to this John. The old arrl books, and w1icp's
notes on the gapped choke used in several handbook amps, state that
the Z of the gapped choke was > 100 K ohms on all bands.
## To calculate RF current through the choke, it was suggested to use
.66 x loaded B+ / XL. That factor's in the min swing of the anode.
## Now, if the B+W 800 choke is series resonant @ 21.450 mhz, the
above formulae is out to lunch. Should we be using .66 x B+ / Z instead ?
## I'm guessing the Z will drop to a very low value, where ever the choke
is series resonant.
> Does a B & W model 800 plate choke have enough inductance to work on
> 160? I thought it did not.
## Well, a buddy inadvertently used 45 uh on a YU-148, on 160m over a
few nights, with no ill effects at all. But the 45 uh choke in question was 18
ga magnet wire, bypassed with 3 x 500 pf doorknobs. It was part of a 2 x
piece
plate choke set up, with the bigger choke being a 180/135 uh choke. Of
course,
with only 45 uh, the vac C1 tune cap had to be increased. 45 uh will..'eat'
175 pf
out of the tune cap.
later... Jim VE7RF
> Lane
> Ku7i
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