VFO-122 AGAIN!!

[sndtubes]

Hey Guys,

I have a quick question about my VFO-122.  I had posted before about stability problems on 20 - 10 meters.  So, I decided to just go ahead and replace all of the resistors and caps.  So, in true form, as I always do, I made it worse!  Now it doesn't work at all on 20 through 10 meters.  It still works on 160, 80 and 40.  I have checked and rechecked my work and can't find any problem.  Now my question is about the caps.  I replaced all of the silver mica's with new, modern silver mica's....shouldn't be a problem.  I ALSO replaced the ceramic caps with silver mica's.  Could that be my problem??  I have tried a couple of different tubes, etc. 

As a side note, I ordered a WA1FFL DDS VFO with the tube gear driver board.  I'm probably going to use it, anyway.  I'm hoping the Viking II will also work on the WARC bands. 

[KZ5A]

I could be all wet here, but best as I recall, the 122 only produces 160 and ~40M frequencies at its output and depends on the first stage in the Viking 2 to multiply the signals for for the higher bands.  So I am assuming that it works in the 160, 80, 40 position but not in the 40,20,15,10 position.

My first guess would be that one of the caps you replaced/installed, that is associated with the 40,20,15,10M position, is either mis-marked or defective. If I'm reading the schematic correctly, C50, C51, C57, and C58 would be suspect.

I have to go down this road myself in the near future, right after getting my Viking 2 reassembled, so will be interested to hear what you find.

73 Jack KZ5A

[N8ETQ]

Yo'

    Be careful with the lenght of coax for the output, seems to shunt them out
pretty good.  With RG-58 at about 30pf a foot, two feet may be too much!
You didn't mention if you changed it but Something to check anyway.
   "At least you'll know what it's NOT" which is almost as valuable as
knowing what it IS!  RG-59 is only 22pf a foot, may help a bit. BTW
some rigs want a 100pf in series with the center conductor like the
Challenger. The thing was originally supplied with RG-59, not sure
how long though.

GL es 73

/Dan

[K9PNP]

I cheated and looked in the book.  Output of the 122 is 7.000 - 7.425 Mc and 1.75 - 2.00 Mc.

The coax line G50 "must be left at the length supplied as it is electrically part of the broadly tuned output circuit".  ["as supplied" is 36"]

"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. The transmitter total input capacity should be between 30 and 40 mmf to center the VFO maximum output in the VFO frequency ranges (the Viking II transmitter has a one foot length of RG59U, the VFO input jack, and the tube input capacity to make up approximately 30 mmf.)"

Mine still has the original coax complete with PL-259 that somebody put on it in a rather haphazard manner and it works fine.  Of course, I still have the original circuitry, believe it or not, and output and stability is still good.  Luck is holding so far.

[sndtubes]

Thanks for the responses so far.   I want to comment on them.

The coax that came with the VFO is still on it.  I didn't change it.  Before I "worked" on the VFO, it functioned.  It probably was functioning as well as a VFO 122 can.   So, it was working with the coax that is on it.  I think its RG59.  It looks original.

I wanted the VFO to be more stable.  It was probably plenty stable for AM work.  But I use it a lot on CW and on 40 and above, it would jump around just a bit.  Like up and down 50 to 100 cycles.  So, I thought I'd just change out the tired old components.  I imagine that when I get it fixed, it probably will still be just as stable or unstable (whichever way you want to see it)

My original question was if using silver mica capacitors in place of some of the ceramics was a problem.  I didn't think it would be, but I'm not sure........

I will be trying out a DDS VFO with the Viking II soon and will report the results.  I'm hoping that it will be stable, chirp free and the Viking II will work on the WARC bands......

thanks all,

Mike WB0SND

[K9PNP]

I tend to agree with Jack.  Also, the caps originally were plus-or-minus 2% and 2.5% tolerance.  I have noticed that most sm caps now advertised are plus-or-minus 5% and some 10% tolerance.  It is possible, though not highly probable, that if all the new caps in the 40-20-15-10 M section were max tolerance in one direction that the VFO may be oscillating, just not where it should be.

I will add from having had it happen to me:  check the band switch, especially if you have done any soldering on it.  I have had a very small number of even the mil specs old ceramic types not work correctly after a little heat has been applied to a solder tab.