[Heathkit] DX-60 VR Tube Mod

[Bwana Bob]

Ken:

I have not tried this mod, but I think that chirp is more a function of 
the crystal or VFO. Back in my Novice days, I noticed that some crystals 
chirped. They were the old surplus type FT-243 crystals. I was able to 
improve one by taking it apart and cleaning it. I had chirp and drift 
with my HG-10 VFO on 15 meters. This was cured by replacing the 6CH8 
tube. Apparently, expansion and contraction of the tube elements was the 
cause. Also, for best crystal stability, it is important to tune the 
6CL6 oscillator plate coil slightly off the peak. It will tune rapidly 
on one side of the peak and slowly on the other side of peak. Offset the 
coil off-peak on the slow side. I actually had crystals drop out of 
oscillation on 40 m if the coil was tuned exactly on the peak.

                                         73,

                                         Bob WB2VUF

On 5/15/2012 1:14 AM, Ken Miller K6CTW wrote:
> All,
>
> 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.
>
> 73 - Ken Miller, K6CTW
>
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