Puzzling problem pairing a Viking 122 VFO and DX-60B

[WA9ZWA]

Hello all

I recently acquired a Viking 122 VFO and Heathkit DX-60B.  The 122's octal plug had been rewired to mate with the DX-60B's accessory socket so I assume they had been used together but had set for many many years before I got them. First thing I did was recap the DX-60B and clean it up.  It's really in good shape.  I hooked it up to the HG-10 VFO (which runs on a separate power supply) that I use with another DX-60 and made several CW contacts and a couple on AM phone. I cleaned up the 122 and replaced the old brittle coax cable that had a PL259 with a cable with RCA plug to mate with the VFO input RCA jack on the DX-60B and built a power supply so I wouldn't have to rob power from the transmitter.  I also didn't want to key the VFO.  I want to run it continuously when in transmit to cut down on the chance of chirping. The VFO seems to like the power supply and I was able to align it with no problem.  Here's the head scratcher.  I was working a couple of CW stations on 40 yesterday and one op, who had a 20+ S9 signal, told me he could hear my signal very weak when my key was up. I got to looking and with the VFO running and the key up I can see a little bit of plate current and the watt meter is showing a few watts output. I tried keying the VFO and he said the hetrodyne went away but it was a little chirpy.

Here's how I have it hooked up.  I have a pair of contacts on my TR switch connected to a 1/4 plug plugged in the key jack of the 122 that lets it run when the transmitter in in the transmit position.  This is exactly the way I have the HG-10 on the other DX-60 and the VF1 on my DX-40 and it works fine.  I have tried the HG-10 and VF-1 with this DX-60B and don't experience this problem when the key is up.  Any ideas as to what would cause this with the 122 and not with the VF-1 or HG-10?

Thanks in advance
Barry
WA9ZWA

[Pete, WA2CWA]

Check or replace the by-pass capacitor at the key jack. If you open the keying circuit and the VFO is still slightly putting out a signal, that cap could be leaky.
Also, make sure the VFO output cable is 72 ohms and, I believe, no more then one foot in length. I believe this is documented in the manual.

[WA9ZWA]

Pete

Thanks for the response.  I want the VFO to run continuously when the transmitter is in transmit.  I am not keying the VFO.  When I changed the VFO coax I did use a piece of RG-58 and it is more than a foot long.  I did this before I read that in the manual.  I can go back to the RG-59.  It's still puzzling how the transmitter is putting out a small signal when the key is up and the key is plugged into the key jack on the transmitter.

Barry
WA9ZWA

[W1RKW]

I would suspect that the transmitter tubes V1, V2 and V3 are not in a full cutoff state. As Pete suggested that capacitor (C2) at the key jack could be leaky allowing the tubes not to reach full cutoff in a key up state.  check the values of R2 and R10.  Is the neon light working properly? it used as a voltage regulator in the bias circuit.

[DMOD]

Here is the Simplified Keying circuit.

Make sure the Bias supply is up to snuff and there is sufficient negative bias for cutoff on Keyup.

Phil - AC0OB

[WA9ZWA]

I am not keying the VFO the VFO runs constantly when the transmitter is in the transmit position.  I tested the same transmitter with a HG-10 VFO and a VF-1 VFO and don't experience this problem.
I will replace the key jack bypass cap and see what happens

Thanks
Barry
WA9ZWA