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Hickok 288X Signal Generator: Removing The Tuning Capacitor For Cleaning

Thus far on the Hickok 288X, I have replaced the electrolytic capacitors, and the paper capacitors.  I also went through the micas, tested them and replaced 6 of them.  And still I'm not getting any frequency output above about 5 Mc (mHz in modern speak).

So I threw out a help me thread on the ARF.  One suggestion was to clean the tuning capacitor.  Since I don't know where else to turn, I'm going to remove it and clean it.

This is the big air variable capacitor that sets the frequency for the generator.  It's pretty much like a tuning capacitor in a radio.  I'll need to unsolder the connections from the tabs on it, disengage it from the drive mechanism, and pop it out.

I did briefly consider just trying to clean it in situ, but then I thought, I'm in this far, I may as well do it right.

I need a reference point of sorts to make sure it goes back together right.  I decide to take it out with the capacitor 'vanes' meshed (actually it's the rotor and stator), which is the very low end of the frequency range.  At that point, the "Band" line is in the middle of the frequency window.  An easy thing to remember.

Plus I have a picture.

This is how the drive works.  On the front panel is a "Frequency Adjustment" knob.  The shaft of that control is shown by the red arrow in the inside picture.  That shaft has a groove that the dial drum/pulley/flywheel's edge rides in.  The pulley is attached to the brass shaft you see in the picture.  Also attached to the shaft is a gear that drives a mating gear on the tuning capacitor.

So turning the knob turns the capacitor, changing the frequency output of the generator.  At the other end of the brass shaft is the frequency readout dial.

I need to remove the dial drum in order to slide the brass shaft back to disengage the drive gear from the capacitor before I can remove it.

Since the dial drum extends through the front panel window, I have to remove about half of the fasteners and knobs holding the front panel down to the chassis.

So I take them off.  I needed to take them off to clean them up, so this isn't really extra work.  They would have had to come off anyway.

The green arrow is one of the drive pulley set screws that needs to come off to move the pulley back.  And the red arrow points to one of the set screws on the frequency dial that needs to be loosened as well.

This is where a camera really comes in handy.  If I forget how it came apart, I have a good reference.

With the knobs removed from the front panel, the whole oscillator sub-chassis can be pulled back, and the frequency dial drum is clear of the window in the panel.  It can then just slide off the brass shaft.

I hope this is worth it.

I like to keep all the knobs and fasteners in a safe place together and labelled.

I figured the shaft would just slide back off the tuning capacitor, but nooooooo!

There's a bracket that holds it in place.  The small screw has a 1/4 inch head - and fortunately there is enough clearance to get to it.

Now I can pry the capacitor up off the sub-chassis.  You can see the fasteners on the bottom - they pop into spring clips on the subchassis.

Now I can clean the capacitor. 

 
 
 
 

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