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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