Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Doc -
I couldn't read your initial message, apparently some coding problem.
There are two chokes in the PA/TR relay area in the TR-3. The three-pi
choke (RFC7) is a standard air core 1 mHy choke and should be connected
from the "hot" terminal on the side of the LOAD capacitor to ground.
It's function is to short the power supply HV to ground if the coupling
capacitors between the final plates and the Pi-Net break down and have
650VDC show up on the antenna. The early TR-4, which still had the same
wired-in relay, moved this choke to the hot terminal of the antenna
connector to ground. This was most likely done to help to bleed off
induced voltage from nearby lightning strikes and to prevent static
electricity from building up on the antenna in dry conditions, but it's
primary function is safety.
The other choke, the simple solenoid on an air core mandrel, (RFC8) 2.5
uHy is to decouple RF from the XMIT CATH line which runs all over the
chassis to the cathodes of each keyed transmitter stage. Its function,
in conjunction with the feedthrough capacitor (C90) is to keep RF
inside the PA cage from being "leaked" out into the under-chassis area.
Your photo looks like the choke may have been overheated. This is not a
problem, UNLESS the wire insulation has been damaged allowing one or
more turns to be shorted. The only way to tell is to measure the
inductance. If even a single turn is shorted, the inductance will drop
considerably. It could be replaced by any air-core choke, keeping in
mind that it has to conduct the entire cathode current of the
transmitter, which can approach half an amp, especially when the final
is off resonance. You could probably closewind however many turns of
#30 (or so) enamel wire that you can fit on a 1M (or other high value)
1W resistor. This choke is NOT needed if you install the plug-in relay
kit from John, since the relay is outside the final RF field.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
On Nov 11, 2007, at 1:55 PM, Halo.net wrote:
"Halo.net" <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>> made
an utterance to the drakelist gang
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Gents,
I'd greatly appreciate a comment or two regarding a TR-3 circuit
question. I'm fairly new to the group and have been following recent
threads with interest. Unfortunately, I’ve not found any comments
related to my question in the reflector or linked websites so will be
grateful for some feedback by members of the group.
I recently re-entered the hobby after a 30 year hiatus and picked up
a TR-3 with an unsalvageable open frame relay. John Kriner supplied
me with a Drake relay conversion kit but a problem surfaced when I
ended up with an extra choke not mentioned in the Drake instruction
sheet. The mystery choke is single wound, about an inch long and the
diameter of a pencil. I had another TR-3 sitting on the shelf for
comparison, but, unfortunately, it already had a kit installed and no
mystery choke connected.
So I contacted John, explained the situation and got this reply: " I
am confused now too. There are different versions of the TR-3. I
don't believe the small choke is used. I think the 3 tier choke
should be un-soldered from the load cap terminal. Run it to the
center of the SO-239. And then connect the other side of the choke
to the load cap frame. Finally, run a wire from the load cap
terminal to terminal #4 of the relay board. I think this will do it."
To clarify things a bit, I’ve posted some pictures of it on the
Halo.net website (see link below). So before I wire it up, I thought
I'd run it by the group in the hope that someone can identify this
particular choke.. is it a Drake factory variation or an owner
modification? Thanks for any help you can give me..
Doc WB6WAD
http://mysite.verizon.net/halo.net/halo05ba.html
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