It is exactly as stated. The adjustment is an old school ceramic trimmer cap conveniently placed on the board in line with the key jack on the rear panel. Since you need key down CW to hear the side tone it becomes a one-handed adjustment to slide a small flat blade screwdriver through the key jack to both key the rig and adjust the trimmer. You do not need to have the drive turned up to do this. How you measure the 800 Hz audio tone is up to you. If you have a frequency counter that works well in the audio range that would be the obvious choice. Simply connect it across the rig's speaker. You could also use an accurate audio generator set to 800 Hz and connected to a small speaker to zero beat the CW side tone using your ears. Another option would be a Windows or Linux computer with the Fldigi digital mode software installed. You can accurately measure an audio frequency with Fldigi.
Extreme accuracy is not required but I would suggest that you not go too far away from 800 Hz as that is the design center of the oscillator circuit. Which also makes the math easier. Drake's CW is a bit different than most other rigs. Modern rigs typically shift the RX frequency to hear a CW tone and the dial displays the zero beat (carrier) frequency. The TR7 is exactly the opposite. We shift the TX up 800 Hz and the dial displays the offset frequency. Your zero beat frequency is dial frequency +800 Hz. If you want to work someone on, say, 7010 you need to set your dial frequency to 7009.2 to be on his frequency.
Re: a bench test jig, depending on the circuit you are troubleshooting you don't always need all the voltages to test a "naked" board. Much of the time you would only need +10. I have swept the IF filters from a couple of rigs using only +10 to turn on the desired signal path and negative volts from a 18650 cell to bias off the other signal paths. I used component lead clippings shoved into in the Molex connectors and alligator clip test leads to make the connections. A bit ugly but it worked FB.
On Sat, 08 Feb 2025 06:48:58 -0800
"atlasstuff via groups.io" <g4fph@...> wrote:
I tried to adjust the CW sidetone on the TR7, but could not understand the Drake procedure for this. Something about a screwdriver and the KEY jack! Are you able to shed any light here, please?
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73
-Jim
NU0C
Jim Shorney
