Thanks, John. I'll make a posting after I've implemented and tested what I
conclude will be the best comrpomise.
73,
-Larry/NE1S
John Coleman ARS WA5BXO writes:
Construction of a push pull circuit is a real difficult project if
started wrong. It has been my experience to find that the plate tank
and grid tank do need to be as far apart as possible if plug in coils
are to be used and they need to be at right angles to each other. Some
folks choose to use a band switched coil arrangement where the grid
coils and switch assembly can be in a completely shielded case of its
own or below the chassis that is sealed up for RF. I have actually used
a Johnson Match Box 500 as a grid drive circuit years ago. It sat on
the desk and I used that 300 ohm shielded cable that Radio Shack, sold
years ago, to feed it to the grids. I put two RF chokes in the Match
Box to attach the grid leak resistor and bias supply to. It worked quit
well. I remember I could adjust the length of the twin lead cable to
get better results on some of the higher frequency bands.
I prefer the switched coil assembly in a shielded box and mounted under
the chassis myself.
You may find more ideas at
http://wa5bxo.shacknet.nu/wa5bxo.qsl/pptriodes/pptriodes.htm
Good Luck
John, WA5BXO
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of ne1s
Sent: Monday, February 06, 2006 2:31 PM
To: AM Radio Reflector; [EMAIL PROTECTED]
Subject: [AMRadio] Push-pull Triode HF PA layout question
Hello all,
I humbly request the experience-based advice of this esteemed group.
Background:
I am working on a project, part of which involves completion of 1930s
Push-pull trode PA deck for 80M - 10M. Notice I said "completion," not
"construction." This deck already has the plate tank components, tube
sockets, and neutralizing capacitors mounted on a beautifull
black-wrinkle
chassis & panel. The axis bisecting the holes for the tubes is parallel
to
the front panel, the plate tank air variable (split stator) is
perpendicular
to the front panel, and the plate tank coil (plug-in jack-bar style -
actually I'll be using BC-610 coils, link-coupled to the antenna) is
centered directly behind the plate tank capacitor, with its axis
parallel to
the front panel. What this deck lacks is a grid tank circuit, which I
need
to add. The tubes will be 812s or T-55s, and will be plate-modulated for
250
- 300W output.
Question:
What is the worse sin: lack of physical symmetry, or proximity of the
gazinta to the gizouta? It seems that I'll have to compromize one or the
other in adding the grid tank circuit, based on the present layout. The
grid
tank will be link-coupled to the exciter.
Thanks for your assistance,
-Larry/NE1S
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