Date: Thu, 6 Dec 2018 22:11:50 -0500
From: "Tim Duffy" <k3lr@k3lr.com>
To: <amps@contesting.com>
Subject: [Amps] Plate choke design L?
<For best plate choke performance on 160 meters - what is the inductance that
<results in best 160 meter amplifier performance?
<Using a 8877 tube here.
<73
<Tim K3LR
## On a 160m mono band amp..with a 8877. 300-400 uh would be optimum.
Assuming plate current of no more than 1 Amp, 27 gauge would easily handle
the job.
With mono band amps, you get to optimize everything.....like the plate
choke..and not have to
worry about a 1st series resonance on say 80-40-30m.
## But you may well have total length constraints...esp if larger gauge magnet
wire used, like 24-22-20.
Is the proposed 160m choke to be mounted vert, or horz ? On hb plate chokes,
I use solid teflon rod,
typ the one inch type. Any coil calculator will spit out the number of
required turns for a given uh, or
wire gauge to fit XXX number of turns, onto a max length rod. If you run
out of length, then increase
the rod diameter, like to 1.125 or 1.25 inch, or even bigger. I drill and tap
the bottom of the teflon rod with
a .25-20 thread, then use a 1 inch long .25-20 nylon bolt, to bolt it to the
chassis.... when mounted vert.
Transverse 8-32 brass screws at each end of the winding to terminate the
windings, etc.
## A lot of amps will feed B+ up through the plate choke, then feed the B+
through the parasitic suppressor,
then to the anode. For better stability, I never feed B+ through the
suppressor. Even if no suppressor used,
the B+ goes from top of plate choke..straight across to anode...and not the
anode connector in the center of the tube,
but the outer ring, at the top of the outer ring, shell. Then the RF path
is from another portion of the outer ring,
over to the plate block caps. Those 2 connections are like 90-150 degs
apart..depending on config.
## Funny you mentioned a 160m plate choke, since Im in the middle of
designing a mono band 160M YC-156 amp
for a buddy, but that is a taller tube than a 8877. Mounting a plate choke on
a side wall is ok too, as long as each end is
supported, and spaced away from any side wall. For 160m use, 2-3 X
4700 uf ceramic bypass caps used at
cold end of 160m plate choke. I use ceramite brand, available from mouser
and also henry radio, since I could get
em in 10kv and also 15 kv ratings. 5 or 7.5 kv would be ample for a 8877,
depending on un loaded B+ values.
Jim VE7RF
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