Kevin -
A scope can be used, although I find it easier to just listen to the
receiver.
Think of the two filter passbands as the letter "M" as depicted on Page
29 of the TR-4 Manual. The goal is to adjust C130 so that it sits in
the valley between the two filters. If you turn on the CALibrator and
tune through it in either direction in receive mode, you'll see the
S-Meter go from noise level up to 10 over S-9 or so for a couple of kHz,
then down to noise again, back up to 10 over S-9 for a couple of kHz,
and then back down to noise level. If you get this pattern, then C130
is close. Fine adjustment is to listen to the receiver noise (no
antenna, high band, no signals) and switch back and forth between USB
and LSB. The 'pitch' of sound should be similar in both positions. If
one sounds low or 'bassy' and the other side sounds high and 'hissy',
then adjust C130 slightly until they sound about the same. They will
NOT sound EXACTLY the same due to anomalies in the filter passbands, but
they should sound similar.
Just in case you are 'really' asking about nulling the Carrier in the
Balanced Modulator, in this case you can clip the ground lead of the
scope to the chassis and then just lay the probe tip near the Driver
tube socket. Set the SIDEBAND switch to "X", key the transmitter in
X-CW with the GAIN at full CCW, and adjust C127 and R85 for MINIMUM
signal. Again, it's easier to listen on an external receiver if you
have one available, and do the above, adjusting for minimum signal in
the receiver.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Kevin Elliott wrote:
I have been reading all of the posts in the new Drake archive and the
old Drake archive trying to learn as much as I can about my TR4. To
you old pros this will be a rookie question, but I am of the belief
that if you don't ask you don't learn. Okay I have read where it has
been said that you can use a couple of different ways to set C130
correctly. One being use a digital receiver and listening for the
matching null and the one that I want to ask about is using a scope to
adjust them. Where will the scope probe be connected to read this
information or is it indirectly connected with a loop of wire around
the oscillator tube to see the nulls.
I got the Great service CD and I love it and will be going through it
and digesting all I can.
Thanks
Kevin _ KG0MN
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