Need help mating Gonset Communicator II with Johnson 6N2 VFO

[nz5n]

Hello folks,

Now that both my Gonset Communicator II and my Heathkit Twoer are working well enough (see my prior threads, thanks to all for the help), my next project is to get them working with VFO control.  Picked up a Johnson 6N2 VFO for the task.

The VFO appears to be working, at least to some extent, the tube lights up and a frequency counter shows output on 8 mhz.  And when connected to the Gonset, there does appear to be a small bit of output at the pertinent 2 meter frequency.  But it is not what it should be, the magic eye barely moves when tuning up (it closes almost completely with a crystal).

There may be an easy solution to the problem.  On page 7 of the 6N2 VFO manual (available at http://qsl.net/nz5n/Johnson6N2VFO.pdf ), it states that, in a "pentode cathode-feedback oscillator," it is necessary to "remove the feedback so the crystal stage does not act as a self-excited oscillator" by shorting out the RF choke in the cathode circuit.  The Gonset has a 6CL6 pentode oscillator (see schematic at http://qsl.net/nz5n/Gonset%20Communicator%20II%20schematic%20no%20parts%20list.pdf ), and it has a choke (RFC 1) on the cathode.  So maybe all I need to do is short this choke.

However, thought I'd ask here before shorting anything.  The Gonset 3357 is a similar VFO designed specifically for the Communicator, but the manual for the 3357 (available at http://qsl.net/nz5n/Gonsetvfo3357.pdf ) says nothing about shorting any choke or making any other mods to the Communicator's oscillator.

Any thoughts?  Should I short the choke (would prefer not to, as this would disable the ability to use crystal control unless some sort of switch is added), or is there something else to try first?

73, Bill NZ5N

[Pete, WA2CWA]

For starters, I would try this: I assume at the end of your VFO cable, you have a two terminal plug that inserts into the crystal socket. Put a 100 ohm resistor across both terminals. Add a .001 mfd disk cap between the hot lead and the pin going into the non-grounded terminal in the crystal socket.

                               .001 mfd
>----------------|---------||--------> hot side of crystal socket
                        |
_from vfo         add
                       100 res. 
                        |
>------ ----------|------------------->ground side of crystal socket

[nz5n]

Thanks, Pete, I will try that.  Out of curiosity, what does that circuit do?  And do you think I need to short that choke?

73, Bill

[nz5n]

Hello,

I took the plunge and shorted the choke, this worked to some degree, but only 2 watts out after tuning and peaking all caps, should be 5-6 watts.  Maybe this VFO just does not have enough output to drive the Gonset to full power.

Tried the 100 ohm resistor and .001 cap as suggested, but this only had a negative effect, power output dropped.

Is this as good as it gets or is there any hope of getting more output?

73, Bill