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Sunday, September 25, 2011

2B Trouble!

So this morning I hear that the solar flux is up around 190 and the higher bands are coming back to life. I turn to my trusty Drake 2-B and turn the band switch from "40" (where it has been parked for quite some time) to "E." E is the position that kicks in the 22 MHz overtone crystal on the 6U8 local oscillator. I eagerly turn the pre-selector to the area where the 17 meter band used to appear and... nothing. Nada. Silence. No band noise. Nothing.

I thought the 6U8 might be going a bit soft. I swapped it out. The problem remains. I twisted that E band coil from one end to the other. Nothing. I cleaned the bandswitch contacts. No joy. Now I'm thinking it is the 22 MHz crystal. But its kind of strange for a crystal to just suddenly go bad... It worked before. The receiver is working on all the other bands, so the problem is really that the oscillator just won't go on 22 MHz.

What do you wizards recommend?

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4 comments:

  1. Get out your GDO and test the crystal. No GDO (shame on you)? Then buil a 'quickie' crystal oscillator. A JFET Pierce or modified Pierce should do the trick. I'll assume you sprayed the crystal socket contacts.

    73 from the current repository of S/N 7431.......Steve Smith WB6TNL "Snort Rosin"

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  2. I also assume that you checked to make certain the other bands are working OK(?)

    73.......S.S. & S.R.

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  3. From what you describe, I would suspect the band switch. It is unlikely that the xtal is bad, but the band switch, with a little corrosion, would likely cause it to stop oscillating. You could jump the switch with some test leads to see if that is it. Also, need to check to see if it is oscillating, with a O'scope, receiver at 22MHz or freq counter.

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  4. Bill - Check the 10K resistor (R20)from Cathode (Pin 8) of 6U8 tube. When you switch to "E", that resistor is shorted from the circuit. Measure across the resistor and see if the VOM reading drops to zero when you switch to "E". Also, check ALL resistors tied to pin 8. They set the operating parameters for the Xtal Osc. One or more resistors may have drifted in value. Also, check for continuity across L11 from the junction of C74 and C73 (wiper on rotary switch) - You should show very low resistance (less than a couple of ohms) to ground from the wiper in the "E" position. Otherwise, I would suspect the Xtal. Best wishes. Bruce - KK0S

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