Drake TR4 USB / LSB Audio Difference

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William van Coller:
I am Busy Restoring A Great Looking Drake TR-4C, but it has me stumped!..
I Have done the complete alignment procedure as per the manual but there is still a definite audio bandwidth difference between USB and LSB-and it would seem it is not filter related-The audio is thin on 40m LSB , but on 80 / 20m this problem shifts to USB-wich indicates a connection with the Drake pre-mixing scheme?...
I have even injected 9Mhz into the IF chain and peaked it , making sure the IF lies dead centre between the Xtal filters.
Adjusting the carrier osc/ bfo does not help...
Does it have a connection with the filter slope?..
Please help-!!
Best Regards, William ZS5WC 73!

Don Trinko:
Did you adjust c-130? You adjust this capacitor so that the audio ( no signal) sounds the same on usb and lsb. This is 5-9 in the TR4C manual. You should here the audio change as you adjust it. Good Luck; Don WD8PTB

Tom Rauch:
If you adjusted the carrier oscillator and can't correct the problem, it probably is a bad crystal inside the filter or perhaps a bad crystal in the carrier oscillator that won't shift all the way on frequency. I've seen both happen.

The oscillator should set exactly midway between the slopes of the two filters.

Crystals in your rig are getting up in age, so it is becoming more likely to have some shift off frequency. If that happens in a filter you have no choice but to replace the offending filter. Whatever it is, it has NOTHING to do with anything but the carrier oscillator and the two filters. Has to be one of the two areas.


73 Tom

Chuck White:
I concur with the possibility of bad carrier crystals.  Some years ago I worked on a string of old Galaxy GT550 transceivers.  They were well known for having carrier crystals go bad.  The symptoms were just as you described.  New crystals allowed proper alignment and correct sound.  Good luck!

73,
Chuck

William van Coller:
Thanks for all the replies-I have adjusted C-130 and the audio is still different-Thin on 40m lSB and 80 / 20m USB.I will possibly sweep the filters and see what the actual bandwidth is.
Thanks, will keep you guys posted if I have any success!..
Greetings and Best Regards, William, ZS5WC

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