Ron -
Nope, the 0.5 V sets 100 mA for the TR-(any). Remember that the AC-3
was designed for the TR-3, before there were any T-4X(any)! The correct
TP setting is 0.35 (.070 * 5) for the T-4X series.
I still like the meter to read as accurately as possible (for a $1
meter!) at least at 0.70 A.
Any "good" _silicon_ diode will have a forward bias of 0.6 to 0.7V.
Perhaps you were looking at a germanium (0.2-0.3V), or a Schottky (0.3-0.4).
Marking isn't a bad idea. You certainly want to turn the pot slowly
until you KNOW which way the current is going!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Ron wrote:
Garey,
I love the idea of the diode, but I would guess 2 series diodes would be
better. The TRany requires .5 volts at the TP. I seen to remember a couple
times when diodes seemed to have lower than ~.6 volts drop. Maybe they were
schotchy diodes or something. Just remember thinking they were suspect.
I also used a permanent marker to mark the min/max bias setting on the bias
pot. Since I set the bias so infrequently, I can never remember which way to
go.
73,
Ron WD8SBB
--- On Wed, 1/13/10, Garey Barrell<k4...@mindspring.com> wrote:
From: Garey Barrell<k4...@mindspring.com>
Subject: Re: [Drakelist] T4Xb meter shunt
To: "Drakelist"<drakelist@zerobeat.net>
Date: Wednesday, January 13, 2010, 10:13 PM
Paul -
Yes, that was one thing that should have been kept in the
AC-4. The
voltage at the test point shouldn't go over a half volt,
(0.35V to set
the Bias for the T-4(any) transmitters.) Unless the
resistor opens up!
I think if I was going to bring the TP outside the cabinet
I'd use a BNC
connector, and make a BNC shorting plug to keep over
it. Probably
wouldn't hurt to put a power diode (1N5408,) across the
jack as well, so
the most voltage that could appear across the jack would be
~0.6VDC.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement
CDs
<www.k4oah.com>
Ron wrote:
Garey,
I took a different approach to setting the bias.
I installed TP of the original AC3 power supply into my AC4
(actually my AC4R). It was an easy modification and
now I don't care how accurate the meter is, or how difficult
the hash marks are to see on the meter.
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