Frequency Hopping Ranger

[KA8JBY]

Greetings:

My Ranger frequency-hops!  Also, the oscillator sounds, well, feeble.  Weak and wobbly.  I think it may be the mica capacitors in the VFO as described in http://amfone.net/Amforum/index.php?topic=4906.msg36820#msg36820
Reasonable diagnosis?

There's also a rf coil (L2 single pi, 52uH) in the VFO that looks haggard.  I looked around at Mouser, Digikey, RF Parts and Surplus Sales of Nebraska, but could only find 50uH or somewhere around there.  Anyone ever replace this coil and/or have a source?

Some background:
I recently (with much help) finished restoring my Ranger.   I did the AD5X mods (a subset of the Timtron mods) with WA1HZK's power supplies.  I also replaced

1.  Many of the resistors (which were in some cases 300% of their rated value),
2.  The drive potentiometer, using the Horizontal Output Transistor substitution.
3.  The regulator and VFO tubes with OB2 and 6AH6, respectively.

This seemed to cure most of the ills (chirp, drift)  for the initial QSOs on the first night.  On the second night, however, the rig was all over the place and the signal was described by on of my contacts as rough and chirpy.  I listened to the signal on another receiver and although the chirp wasn't nearly as bad as it had been, the tone was terrible - weak and wobbly, occasionally jumping so far off frequency that I had to re-tune the receiver to find it.

73
Rob

[WA1GFZ]

Deoxit the VFO tube socket. Check bearings on VFO tuning cap. Sounds like a mechanical problem. Could be loose hardware. Coils don't wear out but may be loose. Check solder joints. Check the screen resistor, I just did a 122 VFO with a resistor measuring 40k....and it was still working. also check wiring on the next stage. Frequency pulling can happen if load isn't stable.

[W1EUJ]

There is value to having (one) junker for comparison and scavenging. While I have few radios, I have at least one for comparison in storage.

[WQ9E]

Adding to GFZ's excellent list of things to check:

Does your Ranger have the keyer tube circuit added?  Problems in that circuit can cause a lot of VFO issues.

Are you sure your 0B2 is good?  I have not looked at the 6AH6/0B2 mod but make sure that the dropping resistor for the OB2 is of the proper value.  Too low a resistance will lead to the 0B2 drawing excessive current leading to overheating and instability; too little and it will be right at the ionization point and also unstable.

I doubt that L2 is your problem but replacing it with a 50uh choke should not be a problem.  It's major function is to isolate the VFO RF from the B+ line.

Rodger WQ9E

[KA8JBY]

Thanks to everyone for the suggestions.
Rodger, it does have the keyer ckt.

It would be nice to have a comparison Ranger to cannibalize; maybe someday.

Now I just have to begin the dismantling process and start checking.

I'll keep everyone posted on what I find.

73
Rob KA8JBY

[Jim, W5JO]

For grins try another oscillator tube.

[AB2EZ]

I had a problem with instability of my Ranger's VFO a couple of months ago...

I checked the things that Rodger and Frank recommended... but, all of those things checked out okay.  In my case, the problem was the following:

There is VFO modification that many people do to reduce FM-ing on 80 meters. My Ranger has that modification. The modification is to connect a short wire from one of the screws on the top of the VFO housing, near the front panel to the tab on the front panel that is near the top of the VFO housing.

While the above VFO modification is a good one, in the case of my Ranger: the wire used to make this connection was very stiff. As a result, any tiny movement of the front panel (e.g. due to microphonic effects) was pressing on the VFO housing... which, in turn, was producing a strain the VFO tuning capacitor... which was causing instability of the VFO.

The solution, in my case, was to replace this stiff wire with a piece of very flexible braid.

If you have such a connection... maybe the solution that worked for me will also work for you.

Stu

[WA1GFZ]

Interesting Stu, The 122 I just did was missing most of the front panel screws but it was still rock solid. I'm actually thinking of adding a cathode follower using the 6al5 tube socket I yanked out of the V2. I notice the VFO drive is lower than using a crystal.

[KA8JBY]

I began dismantling the Ranger today in search of the warble.

I tuned it up before working on it.  I noticed the oscillator current was up around 22-24ma, like it is supposed to be and where it was the first night I had it on the air.  On the second night - the night the tone was feeble and jumpy -  the oscillator current would not rise above 18 ma.  So today the tone was strong, but still shifty.

Stu, my Ranger does have the mod you wrote of and it is indeed a piece of stiff wire.  So, I'll go ahead and replace that with some flexible braid as you described.  I had the cabinet off the radio and disconnected that wire just to see what kind of change it would make.  The VFO frequency did change a bit when I removed the wire, but the VFO continued its sporadic warbling/shifting.

Speaking of mechanical influences, I noticed when I put pressure on the top of the front panel, or on top of the VFO box, the frequency shifts.

The warbling occurs, however, when I'm not interacting with the rig in any way and this makes me think it might be something beyond mechanical.

The bearings on the variable capacitor didn't seem sloppy.  A screw on the coupling between the capacitor shaft and the VFO reduction drive was loose and could permit some play, so I tightened it.  (note this was not one of the screws that holds the shafts, but a screw that held the metal piece to the ceramic disk.)

The only other issue I've noticed so far was the OB2 regulator didn't seem as snug in its socket as I'd like.  I'll look more closely at that.

Now I'm going to start checking resistors and solder connections, and cleaning the tube sockets.

That's all I have to report for now.

73,
Rob

[W3NP]

Rob,
I just recently had the same issue with my Ranger. You didn't mention whether the instability occurs on both bands (80 and 40) or just one. That is a clue as to where the trouble might be.

I found that the bandswitch inside the VFO compartment was the main cause of my grief. I don't know whether you attempted to clean it when you were in the VFO but often times if a switch in a frequency sensitive circuit is just given a shot of De-oxit or some other cleaner, it ends up creating a problem when dirt, oxides, etc are washed onto the ceramic after a period of running at operating temperature. I ended up flushing my switch out real good with a non-lubricating, non deposit leaving solvent followed by a light brushing with some 91% isopropyl alcohol, and then an ever so light application of De-oxit - just a tiny bit that will not run but just "coat" the wiper with a fine film. I did the same thing with the wiper on the tuning capacitor (at the rear) and also the trimmer caps.  Of course all of this requires removal of the metal enclosure that surrounds the VFO and that requires the front panel to be removed.

I had the same warble and jump that you described and after the above procedure the VFO is very stable after the normal drift during warmup. Try cleaning before you start replacing any components. If you still have a problem, then you could possibly have a bad capacitor in the associated tank circuit - either the 500 or 1000pf micas or even the TC caps. Start replacing parts only after all else fails. BTW - my L2 choke looks nasty too but works fine.

My problem also began after working on (disturbing) the switch contacts that had been slowly grunging up for 50+ years.

Good luck.

[KA8JBY]

NP, thanks for the tip - I have the VFO cover completely removed now, so it's a perfect time to go in there and re-visit the band switch.  I cleaned it up when I was restoring the rig, but as you suggest, may have dislodged just enough gunk to create more problems.

You (and others) mentioned de-oxit.  I don't have that particular brand - I've got some Techspray general purpose contact cleaner I got from Mouser.  Is the de-oxit different?  Should I invest in some of that to squirt around (instead of the Techspray) before putting this all back together?

In other news...
I found a spectacularly loose .005 mfd  capacitor (C20) that was not grounded.  So I'm fixing that up, too.

Cheers,
Rob

[W3NP]

The contact cleaner you have is probably fine. De-Oxit is a popular cleaner, but it is not magic or anything. I have had many favorite contact cleaners over the years, some which are no longer available. The main thing with using spray cleaners is NOT to SPRAY the switch using the "firehose" approach, especially those with phenolic wafers. It will soak into the material and can often ruin the switch. I have seen quite a few switches that have been trashed in this manner. Since it is very difficult to modulate the button on a spray can to just get a drop out, I usually spray a little onto something, like a screwdriver blade or whatever is handy and then just administer a tiny drop onto the switch wiper with a very small screwdriver or sometimes even a tuning tool. Only a tiny film is needed, anything more will not do a bit more good and is usually detrimental in the long run. I do like to keep a can of "Tun-O-Wash or something similar on hand. It is a non-residue leaving solvent that was popular back in the days of TV tuner turrets. I use it to clean the switch before applying the De-Oxit.

BTW: De-oxit is available in a small pen type applicator and that works fine but is almost impossible to get into rotary switches or other tight places with it.

My Ranger is back together and so far, rock solid.

[KA8JBY]

Dave:

Thanks for the good advice - I was considering one of those pen or needle-type applicators until I read your post.  Unfortunately, I used the fire-hose approach on a couple of the switches with the Techspray, - but the wafers were ceramic, so hopefully there wasn't much damage done. 
I also found that Simichrome  polish on the end of a long cotton swab was effective at removing a lot of the gunk/tarnish on the moving portion of the switch.  However, it does nothing to address the stationary portions.  I typically followed the Simichrome with the Techspray. 

73,
Rob KA8JBY

[WA1GFZ]

Tarnished silver is a better conductor than spit shine.

[w3jn]

It's never a good idea to douche something heavily with contact cleaner.  As Dave mentioned, just a *little* is more than adequate.

Spray a bit of that cleaner into a bottle cap or something, and use a Q-tip to wipe the rotor contacts of the switch.  Crank 'er around a few times and it should be FB.

Another thing that's often neglected is the wiper on variable capacitors.  Usually there' s a little brass finger that contacts the shaft of the variable.  It's well worth cleaning with a burnishing tool, or a piece of thin cardstock wetted with contact cleaner.  DO NOT SPRAY IT on the variable cap.

[W3NP]

First time I ever heard of anyone using Simichrome to clean switch contacts. I used to use that stuff on my 72 Harley Sportster back in the day - works great on engines. I did a quick google on it and the main ingredient is metallic.

Simichrome seems to work magically, with very little elbow grease needed to dissolve/remove surface stains and oxidation (the main ingredient is aluminum oxide).

So you were coating your switch with aluminum oxide which was removing, by abrasion, the silver oxide. If you then sprayed the switch with contact cleaner, all of this metallic residue got washed down into the switch. This certainly could have caused the freq instabililty problem that you encountered.

As Frank, mentioned the silver oxide coating is a good conductor. Regardless of how tarnished the silver on the rotor looks, there will be a very thin cirular bright shiny line where the contacts "wipe" the rotor and that is the only place(s) on the rotor that actually does the work. These switches are actually "self cleaning" by virtue of the wiping action of the contact against the rotor, so the only real reason to "clean" them is to remove gunk, dirt, etc that may be getting lodged in the contacts and being drug around the switch by the rotor.

I would advise against "polishing" switch contacts, especially with metal based abrasives.  I hope you didn't polish away the thin silver plating.

[KA8JBY]

Was it a bad if I used a Dremel Moto-Tool and a grinding attachment to "touch up" some of the contacts   

Just kidding.

I took a look at some of the wafers I haven't polished up and/or hosed down.
Indeed there was a silver streak.

On the switches I've already attacked, the silver seems to have remained.   Although I was using an abrasive, I was gentle and conservative in its application.  I was under the impression the oxidation was not desirable.  (based on the earlier recommendation of De-Oxit, which the manufacturer suggests removes the oxidation chemically).

The most striking direction on my can of contact cleaner was to make sure it was aimed at the component and not at the technician before applying.  I have followed that advice.  JN's method of controlling the application sounds good.  Thanks also for the tip about the variable capacitors.  I hadn't thought to look at those.

[WA1GFZ]

While you are under the hood check all hardware. Careful not to crack coil forms though.

[KA8JBY]

Well, it turned out the frequency hopping was the result of damage to the variable capacitors in the VFO.  I've attached photos.  Thanks to the diligent detective work of Virgil Leenerts, W0INK, the problem was diagnosed and remedied.

I can only imagine I damaged the capacitors while replacing the out-of-tolerance resistors within the VFO.

In any case - problem solved.  I owe a great debt to Virgil, who patiently guided me through rebuilding the Ranger's power supply and corrected the various problems I inflicted with my "golden screwdriver".

He also helped me update a power supply design for an ARC-5 transmitter which my son and I then built.  The ARC-5 was subsequently, successfully put on the air.

Thanks to everyone for their suggestions and assistance.
Nothing beats a good Elmer (or Elmers).

73,
Rob