[Heathkit] Fwd: Re: DX-60 VR Tube Mod

[KA4INM]

    Ken Miller K6CTW wrote:

> I have been having a lot of fun restoring and using this old DX-60 but have noticed that I am getting a little bit of chirp on 20 meters when using a VFO or crystal.  The chirp is more pronounced on 15 meters.

> While reading the 1961 QST review of the, then new, DX-60, the author recommended (in the Keying and Modulation), that a builder might want to run an oA2 VR tube into the circuit from the screen (pin 8) of the 6CL6 oscillator tube (V1).  The author indicated that this helped clear up a chirp he noticed in the rig on 15 and 10 meters.

> Has anyone on the list done that mod (or used zeners instead of the oA2)?  If so what were your results?

> Thanks in advance for any ideas/suggestions.

   The gas tubes have a negative resistance region, this allows them to oscillate.
Zener diodes do not.  They can not oscillate.

   I would leave the old tube in place (and possibly rewire to put B+ on it through a 47 k Ohm
resistor or something) to make it light if you are into that sort of thing, but I would use a 100
Volt Zener diode on the oscillator screen to regulate the Voltage lower.