HW-101 The Saga Continues

[K7SZ]

Well, when we last left off, we managed to lick the oscillation problem on 15 meters by grounding the tube socket center pins to the shields between the drive plate and grid circuit boards below the chassis. 

AND, we were in the middle of rebuilding the two Jackson Bros reduction drives on the VFO. 

First the drives: After trying to rebuild four of them ( I have a spare VFO out of a parts radio), I am firmly convinced that it would be much better and a lot less frustrating to buy new drives! That is the way I am going as soon as I find out a source (on this side of the Pond) for the drives. 

Rebuilding the drives resulted in a "gritty" feeling after being repacked with white silicone grease. The drives don't exhibit enough "stickiness" to enable the dial to be calibrated when pushing on the toggle button on the front of the bezel and rotating the main tuning knob. Short of repacking the drives with a combination of chunky peanut butter and sand, I am at a loss. Ergo, new Jackson Brothers drives are in order. 

Shortly after "rebuilding' the drives, we were taking a serious look at the VFO itself and decided to rebuild the entire subassembly from the get-go. The chassis was stripped out and new wiring run for the tube filaments. The wires coming from the VFO coil and the VFO Output coil were shortened dramatically (over 3/4 inch was cut from each wire!), in hopes of increasing stability. The large disc ceramic cap on the VFO coil was secured to the side of the VFO chassis with double sided foam tape, resulting in a very sturdy method of insuring that cap doesn't move around. 

The VFO was put back in the 101 and seemed to work. Unfortunately, whoever wrote the instructions for aligning the VFO was either off his/her medication that day or had no idea of really how to do the procedure. The manual is a bit confusing, even to some of us who've been in the business a while. 

We unplugged the VFO output coax, substituted a short coax jumper with an RCA plug for the VFO output terminated in a 47 ohm resistor. A high impedance counter was connected across the resistor and the VFO trimmer caps and coil adjusted for end-to-end linearity. Once plugged back into the rig, the VFO played fine and the calibrator markers were where they should have been. 

At this time we are starting to experience an oscillation that is NOT frequency or band dependent. It varies with the RF gain control, and by reducing the RF gain about 1/4 turn, it goes away. It oscillates in either USB or LSB (didn't try CW), and either wide or narrow IF filtering. I am thinking it is IF related, since it does not vary in amplitude or disappear when the bandswitch is changed. It is a very annoying whistling/oscillation. By zerobeating the dial, then moving off zerobeat either above or below, the oscillation suddenly starts. Anyone have any ideas?

73 Rich K7SZ

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