The AM Forum

How do I know if I've put the phasing knob back on right?

I took it off to clean it and may have put it back on incorrectly. It's time to check the alignment so I'd like to get it right. I surmise that it controls a variable cap that pulls the selectivity crystal frequency.  It supposed be at '0' when determining the frequency of the crystal so the IF can be aligned to match that frequency.  Is '0' maybe half of the amount it pulls the rock? Is it minimum capacity?

There is a spot where the high frequency noise goes up either direction which is 180˚ from where the '0' is now. Do I have the knob upside down?  Or how about the spot where the crystal calibrator has the highest S meter reading which, I think is the same spot?

 

0 is the NULL as you rotated the control.   Just put a signal into the rig or key up a radio near by.  Turn Xtal filter on.  Rotate knob until the S meter is in the null and reads low.  Then loosen the knob and set the reading and zero.  Your done.

C

Thanks

You should have two nulls, each 180 degrees opposite each other, one being at the 0 point on the knob.  To do what Clark says assumes the mica  cap on top is set correctly.  If the filter was not aligned correctly, you will have to visually assure the phasing varible is set at 1/2 capacitance and then do an alignment.  Once set correctly you adjust that mica for the null to be 180 degrees out as Clark described.

Some sets had a mark on the shaft so you knew where the cap set point was.  If you didn't see one and your null is wrong you will have to open the box to see.

How do you get into that can? Is it possible to do with the cabinet on?

I tried adjusting C36 without opening the can with zero success. The nulls are about 90 degrees apart. I would love to get in there to see what's going on with the mica caps and to put an alignment mark on the shaft of the phasing  variaible cap but it doesn't look easy.

You will have to remove the filter box to get it apart.  Just be very careful to not break that phenolic shaft.  I don't know where you could get a replacement.  If you are careful you can remove the knobs then unsolder the wires under the chassis.  There are some metal screws that hold it to the chassis, remove them then tilt the box backward carefully and lift up.

Once out of the chassis everything will be evident.

Thanks especially for the warning about the phenolic shaft.

That was the regular procedure in the Service Dept. That may even be my mark but Im not doing autographs this week ;D ::)

Carl
KM1H

Where was the traditional place for the mark? On the top when the cap is half engaged? On the top when it's fully engaged? I would like to follow your lead so I don't confuse someone who knows where to look.

Half engaged and reinstalled after being repaired with a new shaft or whatever else was needed after some owners got loose in them. Hams were usually careful, commercial users often didnt give a damn.