Johnson Viking VFO 122

[N6YW]

Those of you who have been following the BC-610-E thread know I am working on implementing a Johnson Viking VFO 122 as the frequency control for the 610. What is really strange is that the VFO worked back when it was used with my Viking II transmitter. I assumed it would work now with the 610 but it doesn't.
I built a piggyback power supply that provides B+ and filament voltages. Checks okay. When tuned to the desired frequency, I see the carrier on my Flex 5K screen and I see that when I switch the exciter switch from off to on of the 610, it appears as expected but very weak. New tube, same result.
So, my question is, I have only a few MV of AC signal on the output of the VFO. I should be measuring at least 5 VRMS. On the bench with the key jack shorted to ground, it oscillates but not enough to drive my 610 at all.
What am I missing here? This just isn't making any sense.
Thanks in advance of your comments.

[Pete, WA2CWA]

Did you read the suggestions under "Operating With Other Transmitters" on pages 22, 23, and 24 of the VFO-122 manual?

[N6YW]

Did you read the suggestions under "Operating With Other Transmitters" on pages 22, 23, and 24 of the VFO-122 manual?

Slaps hand against forehead...
The Viking II has the buffer built in. I get it. I will build one.
 

[N6YW]

Still, I was (and still) under the assumption that the 122 already has sufficient output to drive the grid of the oscillator in the 610. As it stands as stock, shouldn't I see at least 5 volt rms?

[KA0HCP]

Still, I was (and still) under the assumption that the 122 already has sufficient output to drive the grid of the oscillator in the 610. As it stands as stock, shouldn't I see at least 5 volt rms?

Not necessarily. 

Paragraph 1.c. on Page 16 tells us that "The output circuit of the Viking Model 122 VFO   is broadly tuned circuit which depends on the output cable and the transmitter input capacity to some extent.  It is therefore impossible to obtain full VFO output with a cable length, between the VFO and transmitter, that differs markedly from that provided with the VFO."

You really need to carefully review the VFO manual.  There are specific recommendations and tips for these issues. 

[N6YW]

Still, I was (and still) under the assumption that the 122 already has sufficient output to drive the grid of the oscillator in the 610. As it stands as stock, shouldn't I see at least 5 volt rms?

Not necessarily. 

Paragraph 1.c. on Page 16 tells us that "The output circuit of the Viking Model 122 VFO   is broadly tuned circuit which depends on the output cable and the transmitter input capacity to some extent.  It is therefore impossible to obtain full VFO output with a cable length, between the VFO and transmitter, that differs markedly from that provided with the VFO."

You really need to carefully review the VFO manual.  There are specific recommendations and tips for these issues. 

Therein lies the problem. My interpretation is the issue. Thanks for pointing this out.

[KA0HCP]

You might consider removing your present coax line that works with your Viking (save for later use) and make up a new one for the BC610.

Note the parts list specifies RG-59/U  (i.e. 75 Ohm)  Three (3) Feet. 

The Assembly instructions caution not to shorten the cable as the length is critical.

-Install the new coax per instructions on Page 7. 


-Perform "Preliminary Checks" on Page 9. This checks for proper output level, and includes specific tips on matching non-EFJ transmitters.

-Continue with remaining alignment and calibration procedures.

[KA2DZT]

If you build a buffer, you may try link coupling the buffer stage to the 610.  Link coupling reduces the effects of cable length.   You will probably need a tuned circuit at the input of the 610.  Depends on where you plan to put the buffer, near the VFO or close to the 610.

Fred

[w1vtp]

If you build a buffer, you may try link coupling the buffer stage to the 610.  Link coupling reduces the effects of cable length.   You will probably need a tuned circuit at the input of the 610.  Depends on where you plan to put the buffer, near the VFO or close to the 610.

Fred

... or a cathode follower.  Either would work.  Might be able to mess around with levels Z etc.  BTW did you guys see this month's ER (October, 2014)?  Has a nice external power supply for the 122.  I might cobble that one up for myself.  I always did like the EICO 722 for that reason.

Al