Re: {Collins} 75A-4 help

Vern, Another thought. I don't know what you mean about jumping the band switch, but understand that it takes very little to upset the oscillator. Touching anything in the close vicinity of the xtal oscillator can kill it. Also, you said you substitiuted C-42. Does that mean you had another adjustable capacitor with the exact same value and actually replaced that cap? When you turn the cap (C-42) under normal conditions, you should be able to peak the oscillation and also kill it. It is very critical.

Anyway, I have to think it is either the xtal for 20 (or it's socket), C-42, L14 or the band switch.

Again, you really need to find out if the oscillator is in fact oscillating before you go any farther.

Let us know what you find,

Joe - KB9R

w0vmp@xxxxxxx wrote:
I still have a couple of problems with my 75A-4 (SN 1788)...20 meters does not work and all receive signals are being attenuated when the antenna is connected to the 50 ohm coaxial input (signals are normal when the antenna is connected to the antenna terminal strip, shield to ground and center conductor to screw terminal #2).

In trying to fix the 20 meter receive problem I have tried a new crystal (Y-4) and have ruled out any problems with C-12, C-27 and C-42 by substituting a new mica capacitor...still nothing on 20 meters.  I have placed a jumper across each set of contacts used on the band switch in the 20 meter position, one at a time, trying to find a bad connection but still nothing.

I have found that the crystal calibrator works normal on all bands except 20 meters...could this be a clue to my problem?

All of the recommended capacitors have been replaced.  All of the other bands align normal and the receiver sounds great.

Looking for ideas, 73,

Omaha NE

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