----- Original Message -----
From: "Donley" <donley...@comcast.net>
To: "Richard Knoppow" <1oldle...@ix.netcom.com>;
<k4...@mindspring.com>; "drakelist" <Drakelist@zerobeat.net>
Sent: Tuesday, July 12, 2011 8:05 PM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Completed tasks.
Adjusted bias control until 0.5 VDC across cathode
resistor, equals 33 mA, three resistors in parallel equals
100 mA total bias current. Bias voltage is -55 VDC at this
point. No bias current measurement on plate current meter
(actually has been just a slight wiggle all along, but
nothing more than a half pointer width wiggle).
C-73 is not a feedthrough, what point should be measured?
My blunder (red face department) I just assumed the C
version was pretty much the same as the plain TR-4 and
looked at my enlarged schematics. Different amimal.
Now to clarify what you see. When setting bias up with
the controls as in the book you see nothing on the meter,
maybe just a slight wiggle. When actually transmitting,
either a CW or SSB signal you see the meter go up-scale and
it peaks with the plat tuning adjustment. I presume it must
also peak with the load adjustment although it may be all
the way at one end.
If this is the case I am sure you are seeing the RF
output. The meter has a simple rectifier that samples some
of the RF output and feeds the DC to the meter. Even though
the spring may be intact and the switch seem good I would
check the wiring at the meter switch (assuming its as
accessible as on the TR-4). Use an external meter to see
what is there. Its possible there is something shorting the
switch or other wiring error there. Don't assume its OK
because it look alright. The meter isn't working right
something is wrong. To be blunt, if all the tube voltages
are present and are about the right values, the problem just
can not happen at the tube. IMO it isn't real, its an
artifact of the meter switch or wiring being wrong.
BTW, I think Garrey Barrell has a DVD for the model, if
he does I URGE you to get it. When you do have the manuals
printed out and bound at Kinko's or someplace. Also have the
schematic printed out _large_ 18X24 or whatever the nearest
standard size is. Get about three copies, they are not
expensive. That way you can mark one of them up. Use colored
pencils or highlighers to trace out the circuits. Drake
schematics are dense although I've seen lots worse so some
visual aid is necessary to be sure your eye doesn't skip
onto the wrong line. Sometimes seemingly complicated
circuits get a lot simpler when you trace them out, for one
thing they are visually isolated.
It may be helpful to re-draw some of the switches to
have a better idea of what they do.
GET THE DISC!!!
--
Richard Knoppow
Los Angeles
WB6KBL
dickb...@ix.netcom.com
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