Re: {Collins} 75A-4 help

Hi Vern,

Are you shorting 2 of the terminals on the antenna strip when you are using the coax input?

As to 20 meters, do you know if the xtal for that band is oscillating? You can probe loosely with a hand held frequency counter or a piece of coax with some center conductor exposed connected to a near by receiver set at the frequency of the xtal. (don't actually touch anything with that coax center conductor! Just hold near the oscillator)

Good luck,

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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