Issues with recently acquired Johnson Viking 2

[WD4DMZ]

Great advice. Thank you.

So far I have the 7295 xtal at 7295.1 and the 7290 at 7289.85. That is close enough for an AM receiver passband and will not crowd other users or the band edge. I did add more capacitance just to see what happened and sure enough over 10pf  in parallel the xtals stopped oscillating.

The 80 meter xtals were a bit tougher but my 3705 and 3740 are both within 100 hz. The 3875, 3880 and 3885 are about 150 off.

All are close enough but if I get a few 1 pf caps I might add them in. The smallest in my parts stash are 3.3pf. Many in the AM windows are on boatanchors so are also off a bit and unless I mention it no one seems to notice unless they are using an SDR.

These xtals are dead on in my DX60 with no caps added so the issue in likely some out of spec caps in the V2 osc circuit.

The guts of the 243 appear to be wire lead xtals intalled in the 243 case so no way to work them.

Next question... I do have a VFO122 that caused the original problem when plugged into the V2. I used an outboard PS and it seemed to function but would not drive the V2 to full power. However, I did not retune the V2, leaving the settings where they were for the xtals. Do I need to retune the V2 whan using the VFO? I'm a rookie with the V2 so do not know what to expect and the manual makes no mention of VFO vs xtal use.

So far the V2 has exceeded my expectations. Great audio using a D104, stable with the xtals, and so far pretty forgiving of my tuning errors.

Regards, Rich

[Tom WA3KLR]

After running a Viking II with just the 122 VFO for a number of years, I added crystals.  Some crystals would not oscillate in the Viking II, but were known to be good in other oscillators.  I found that the oscillator stage has an "un-bypassed" screen grid (the plate in an electron-coupled oscillator).  After research into other Johnson transmitter schematics, I added 10 pf to ground at the 6AU6 screen grid.  This provided more feedback and more defined load capacitance. The crystals will run somewhat lower frequency after this modification and crystals that may have not run, will now (if they are good).  Another change I made was to change C14 from 50 pf to 62 pf.  I wouldn't add 10 pf across the crystals but do these 2 mods and this will have the same effect and will provide a more robust oscillator for operation with less active crystals.

I will attach a tuning cheat sheet I made many years ago.  On 1885 kHz I found that the oscillator tuning with a crystal operation should be 57 rather than 25 in the table entry which is with the 122 VFO.  The cheat sheet files are pdf, and xls for those who have Excel will then be able to change the table entries.

[WD4DMZ]

The files and info are very helpful. Next time the V2 is on the bench I will add the caps to the 6au6.

Thanks, rich