The AM Forum

Hi everyone,

I'm hoping that someone can help me crack this nut I've been trying to fix for the past couple of weeks.

I have a Johnson Ranger with the early keyer platform.  I've replaced all the electrolytics as well as R3 with a 5W 18K metal resistor.  The usual stuff.

I primarily operate CW.  When I have it on 80m, either when zeroing or transmitting, the CW note is rock solid.  However, when on 40m or 20m, the CW note drifts down in frequency, even after warming up for an hour.  This is whether I am zeroing or transmitting into a dummy load.  

Aha, I thought.  Must be a problem in the 40/20 section of the VFO.  So, I replaced the temperature coefficient capacitors (C10, C11) with "dog bone" capacitors of the appropriate types as well as the mica capacitors (C12, C13).  (I got the N150 and NP0 capacitors from Surplus Sales of Nebraska -- they didn't have the exact values so I had to mix and match values in parallel to add up to the correct values.) I also cleaned the band switch in the VFO with deoxit.

Still no luck.  VFO drifts in 40m and 20m.  Oddly enough, when I push on the VFO knob (or on the face around the VFO knob) with everything back together, that makes the VFO go up in frequency with the pressure.  I made sure all the screws and nuts were tight for holding the VFO box together.  The top of the VFO is grounded to the face of the Ranger with a short connection.  I tried W8JI's recommendations for grounding the plate tuning capacitor to the chassis to fix drift.  That didn't cure my issue, so I put the insulator washers back.

I swapped the 6AU6 with a 6AH6 and that didn't fix the VFO drift.  I also monitored the voltage at pin 1 on the OA2 regulator and it stays around 149VDC, only dropping 0.4V on transmit.  I also replaced all the mica capacitors in the VFO as well as any suspect resistors, even though they're not part of the 40/20 circuit in the VFO.  

Any ideas as to what might be causing my VFO drift woes?  I don't get it -- my Valiant's VFO, which is basically the same VFO, is rock solid.  Thanks for any ideas.

73 and Happy Thanksgiving!

Tony W1TTL

Just a thought but in light of the change when putting pressure on the switch, possibly a poorly contacting wafer switch segment?

Hi W1NB,

Thanks for the reply.  Unfortunately, it's when I press on the VFO knob that the pitch changes.  It's like playing a theramin!

73,
Tony W1TTL

Try pressing on the knob/face with something nonmetallic (a pencil?) and note if the frequency still changes.  If not, I'd guess hand capacitance is coming into play somehow.

I would closely check the contacts on the bandswitch, i.e., check and make sure no two adjacent contacts are making contact or bridging.

I have seen phenolic wafers so worn that nothing aligned properly.
Phil - AC0OB

try cleaning the grounding wipers on the tuning capacitor

Gentlemen,

Thank you for your suggestions. I made sure all the contacts were good on the bandswitch and cleaned the wipers on the tuning capacitor as well as the trimmer capacitors for the 40m band.  It still drifts on 40/20 but not 160/80.  The funny thing is when zeroing, the tone is pretty stable.  However, when transmitting CW, then the tone begins to drift.

73

as I recall there are 500pF and 1000pF padder caps in the vfo, 2 of each.  Please replace with dipped mica and see if this does not help.   

Thanks for the suggestion but I did in the original post.  I replaced the two 500pf mica caps for 40/20 and the two 1000pf caps for 160/80.  I replaced them all with modern 500V mica caps and no change.  I then replaced the two 500pf modern mica caps (since they are part of the 40/20 circuit in the VFO) with NOS mica CM35 500V axial caps and no change. 

I am starting to think that putting two temp coefficient capacitors in parallel to equal the correct capacitance for C10 and C11 might be the issue.  If I move a pair close together or far apart with a non-metallic tool, the VFO frequency changes while I do this.  Until I can get the correct valued temp coefficient capacitors for C10 and C11, I won't know if this is the problem.

73,
Tony W1TTL

NOS parts have given me trouble in the past.  You can order new NP0 capacitors from places like Mouser, you might want to consider giving that a try. 

73 - Steve, KW4H

Hi Steve,

Thanks for the suggestion. Unfortunately, that was the first thing I tried. I wasn't able to locate a new N150 (EIA code P2G) 47pF 500V capacitor for C10 or a NP0 (EIA code C0G) 62pF 500V capacitor for C11.  I tried Mouser, DigiKey, etc. to no avail.  If you know of a place that has these capacitors, please let me know.

I think my only option at this point is to find another Ranger and get what I need from its (hopefully working) VFO.

73,
Tony W1TTL

Hi Tony,

The 62pf is here:
https://www.mouser.com/ProductDetail/KEMET/C315C620JCG5TA?qs=sGAEpiMZZMt7gvpyg0xT8gvmgGbgs8vbwfBGBjx3o5A%3D

And the 47 pf is here:
https://www.mouser.com/ProductDetail/KEMET/C322C470JCG5TA?qs=sGAEpiMZZMt7gvpyg0xT8i1GkzbeLodEfKIIhMXuS6Q%3D

The Mouser searches can be tricky.  The 47pf is a C0G/NP0, which means the temperature coefficient is zero.  A P2G has a temperature coefficient of -150.  Does it matter in your case?

Steve, KW4H

Hey Steve,

Good find!  I didn't see the 62pF NP0 on Mouser.  Thanks.

Unfortunately, following the Ranger parts list, the 47pF needs to be N150 (P2G). 

73,
Tony W1TTL

I'll do some additional looking around.  I can't believe that 47pf P2G is unobtainium or only NOS.

Steve, KW4H

NOS isn't my first choice, but here's a site with the 47pf.  It's also a fellow ham, which may carry some weight.  It's not 500v but if you contact them it might be there.
https://kc9on.com/product/capacitors-n150-temperature-compensated-50v-1%E2%80%B3ls-ceramic-disc/

As an aside, I know how frustrating it can be to find some of the parts we need.  We all get in the middle of our various boat anchor projects and want to scream when we're "almost there" and then "that" part creates a problem.  Been there many times, but the fight is worth it.  

My only advice beyond this is to avoid FleaBay if you can.  I'd guess that about 75 percent of the components I've bought from sellers there ended up being landfill material. 

Steve, KW4H

Tony -- one other thought.  Is the 500v rating actually required?  What are the real voltages in play?  Looking at the section of the schematic you posted -- those capacitors are part of the VFO tuning circuit, which may not have a lot of voltage running around in it.  You might be able to replace it with that 50v capacitor just fine.  Or maybe not -- but it's just a thought.

Something else to consider is to circle back on those capacitors from Surplus Sales.  If they were indeed N150 and paralleled to equal 47pf, it should have worked fine.  Since they didn't, there's a reason for it.  It's entirely possible that the capacitor replacement was fine, but the trouble is coming from somewhere else.  

I feel your pain, OM.  Can't count the number of times I was "so sure" I'd nailed a problem, only to be led on a wild goose chase.  It's part of the fun of restoring these boat anchors and keeping them operating.  When faced with such a situation, I recommend a step back and a nice Chardonnay.  I've got a NC-125 here that's been kicking my butt for weeks.  Finally had to set it aside and work on a Hammarlund for a while.

73 - Steve, KW4H

Steve,

Thank you OM for your notes.  It helps to know I am not the only one who gets close to the finish line only to have a boat anchor say, "Haha!  And you thought I could be stable!"  

That is a good question about the actual voltages that are running through C10 and C11.  The 6AU6 in the VFO has a typical voltage of 310V per the manual.  My guess it's around that.  I could open the side panel of the VFO to find out for sure.  However, a Chardonnay would do me right at this point as I have taken apart the VFO at least 10 times chasing this ghost... and anyone that needed to take apart a Ranger's VFO knows that it's no picnic!  

Thanks for doing some research and finding that 47pF 50V N150.  So close!!!  And thanks for your advice.  I will keep looking.

I found this post on QRZ about a similar request and contacted the ham who said he had a NOS 47pF N150 500V cap:
https://forums.qrz.com/index.php?threads/need-temperature-coefficient-capacitor-for-my-johnson-ranger.740141/page-2

I will also contact the ham at the website you linked.

At any rate, I have been using the Ranger on 80 with my newly restored Thunderbolt.  I figured I might as well enjoy it as much as I can.  However, I have AC hum on the signal when I turn on the Thunderbolt.  I am currently waiting for a differential high voltage probe to arrive so I can see where the AC is getting in...

As you said... so close!  At least you were able to find the NP0 capacitors I needed.  It's gotta be these two capacitors that are causing the drift. The nice thing about the Ranger's VFO is that a different circuit gets switched in for 80/160 and the 40/20 circuit gets switched out.  Since the VFO is stable on 80/160 but not in 40/20, then by process of elimination, I am 99% sure the problem lies in the "switched in" 40/20 circuit (in the upper left) of the schematic I posted.  Alas, there is always that 1%, though.

Hope you get the NC-125 working soon.  I have a NC-300 I use for receive and I love it.

TU and 73,
Tony W1TTL  

Resurrecting these beautiful old boat anchors can at times be a frustrating process.  We "almost" get it fixed and then want to bang our heads on the pavement.  But for me, it's the "puzzle factor" -- there's a great deal of satisfaction in turning on a radio that you enjoy, and you fixed yourself.  The learning experience is also well worth it.  I've been working with electronics since I was 14 and even have a pieces of paper somewhere that says I'm trained in it from several institutions and passed exams.  Doesn't matter -- I still get my butt kicked plenty of times.  Everything is a new experience.

For example:  the NC-125 on the bench had a series of previous owners who must have been mad scientists.  I've removed, cleaned, and reinstalled the entire band switch assembly as well as removed, cleaned, and remounted the main tuning cap.  It's still giving me the finger.  Something inside the radio is arcing and blowing QRN over every frequency.  I've pretty much narrowed it down to the primary of the first IF transformer -- it's most likely arcing.  Dealing with that is complicated.

Steve, KW4H

Tony,

   I will delve into the 1% possible areas....For me, it seems nearly 100% of the time, as luck will have it, that is hand I am dealt.

A couple of things come to mind.

On 80m, the VFO is doubled from 160m. That is a good thing because isolation of the VFO is better, even though any drift gets doubled.

On 40m, the VFO runs on 40m...an invitation for regeneration from a later stage back to the VFO...even when using a dummy load. If regeneration exists,

then there could be a temperature constant in play beyond the VFO; even a DC operating point shift of a VFO buffer stage could cause drift. Does the buffer, multiplier, or PA tuning shift the VFO frequency at all? If so, you got regeneration.

The VFO tube, and the buffer tube will both see a drop in filament voltage when you key up. It might be minimal, or it might not be.

I have played with VFO tubes with a variac on the rig. Varying the AC from 110vac to 120vac should yield very little drift. Sometimes a VFO tube

will move a lot under this test. If you got several tubes, you might see a big variation tube to tube where you have a clear loser, and a clear winner.

On 40m, the cathode to filament capacitance will be more significant than when the VFO runs on 160m (for 80m).

What about the keyer Tube, and pot adjustment? Is something amiss there that has a larger effect on 40m?

You might ponder these items...

Jim
Wd5JKO

Jim,

Thank you for your suggestions!  I will investigate those areas...

73, Tony W1TTL

Jim (or anyone...),

I got my hands on a 14.040 crystal and, wouldn't you know it, the CW drifts up and down like a drunk driver with the crystal. Both in standby and transmit and after being on for over an hour.   Any suggestions on where to start looking?  I am assuming now that it has nothing to do with the VFO and with the finals.

On 80m with the VFO, my CW tone is rock solid.  No drift at all.  Great reports.

Is there a stage where the oscillator would drift around like that only on 40/20m, even when using a crystal?

Thanks and 73,
Tony

Tony,

   It sounds to me that the crystal is not determining the transmit frequency. I could be wrong, but with a lot of Johnson gear, to get on 20m, you need a 40m crystal which is then doubled. For 15m, it is tripled, and 10m, it is quadrupled. Check the Ranger manual. If my presumption is true, then when set for 20m transmit, the oscillator plate tuning wil be set for a 40m peak, not 20m.

Jim
Wd5JKO

Jim,

Thanks for the point in the right direction.  You are correct.  I need to use a crystal 7.000MHz and up on 20m!

I popped in a 7.100MHz rock and sure enough, on transmit or "tune," the CW note is stable both on 40m and at 20m (as 14.200MHz).  So, my drift must be in the VFO...

I'll have to keep digging into this problem...

Thanks,
Tony W1TTL

Tony,

When your replaced the current limiting resistor for the VR tube, did you put the replacement in the VFO compartment?  It needs to be there to help stabilize the VFO temperature in this very hot running transmitter.

Check the 40 meter "high" and "low" trimmers to make sure dirt/corrosion on one of them isn't the issue.  Take a close look at the mechanics of the 40 meter coil winding and also C1B to see if there is any mechanical issue present that is affecting the 40 meter section of the coil or variable cap.

If by chance the rotor has shifted slightly in relation to the stator plates, that will greatly increase frequency shift with temperature change.  The plates of the rotor need to be dead centered between the stator plates.

Rodger WQ9E

Hi Rodger,

Yes, I kept the R3 replacement inside the VFO.

The 40m high/low trimmers were a little squirrely so I hit them with a little deoxit.  I also hit C1A / C1B with deoxit, too.

For the 40m coil winding, do you mean L1A in the VFO?  If so, I will check it.  And thanks for the tip about the rotor (SW1) -- I will look closely at the contacts.

73,
Tony W1TTL

If you get into replacing those low value temperature compensating capacitors, I suggest that you heat sink the leads.  Too much heat from a soldering iron or gun could possibly damage them.

That was a trick from an old ham friend of mine.

Tony,

You are welcome and yes I was referring to the 40 meter winding.  I wonder if some turns are loose on the form.

Rodger WQ9E

Hi all,

    I am monitoring the AM Rally on 7295. One guy with a Ranger, has a carrier with significant warble when my receiver is offset in SSB mode to get a tone. The carrier has a sub audible shift when the transmitter gets modulated. I attach a screen shot from my Flex 3000. Notice that this guy has very little upper side-band.

    A guy came back with a Valiant, and that guy had no lower sideband! His carrier was also raspy, but the tone change with modulation was immediate....I could copy him when switching to FM!!

Bottom line....Keep the Johnson gear off 40M AM when using the internal VFO.

There seems to be some sort of regeneration when on 40m where the VFO runs at the same frequency as the RF output. Perhaps this is fixable, but more than likely fixing this will be a challenge because the design, not faulty components, is the root cause.

Jim
Wd5JKO

Jim,

There are fixes for RF getting into the VFO in these Johnson rigs causing frequency modulation of the VFO when the final is on the same frequency as the VFO.  It could occur on 160 meters also but I have not experienced any problems on 160 with the factory stock rigs.

W8JI provides a thorough analysis and fix on his website:  https://www.w8ji.com/johnson_vfo_chirp_jump.htm

Rodger WQ9E

Tony asked me to add my Ranger VFO experience to his thread so here it is.  ;D

I too had drift problems with the VFO on 40M and above, but mine was not a slow drift. It was stable for the first 15 minutes or so, but then it would suddenly QSY down the band FAST - like somebody spun the dial. I suspected C20, the tubular ceramic 47pf N150 temperature compensating capacitor. I had read somewhere on the web that these caps can break down after being subject to extreme heat. Indeed, my VFO showed signs of past Chernobyl meltdowns, and the cap body had black and brown scorch/bake marks on it.

Of course getting an exact replacement for that cap is impossible. Surplus Sales is sold out, and DigiKey, Mouser, etc. don't carry modern equivalents. So I figured I'd try something close and see if it worked. I located some NOS 39pf N150 1000V disc ceramics and installed one. The 40 LO and 40 HI trimmers have plenty of range, and I was able to zero it in to proper dial calibration without trouble. So this tells me a replacement need not have the exact pf value, several pf higher or lower will work.

The original Ranger assembly manual calls for this cap to be installed 1/16" away from the oscillator inductor. As I understand it, C20 is intended to compensate downward as the 40 M side of the inductor heats up and expands. So it makes sense that this cap needs to be really close to the oscillator coil so it experiences the same temperature variations.

Good deal with reducing the drift.

The question remains though, when on 40m does it FM, or end up with one sideband partially suppressed?

Jim
Wd5jko

The suppressed sideband phenomenon appears to be caused by RF getting into the VFO. In my case, what cured it was the W8JI modifications (https://www.w8ji.com/johnson_vfo_chirp_jump.htm) and also tightening up the spring contacts grounding the plate and buffer control shafts to the front panel.

I have not tried this, but according to AB2RA: to avoid non symmetrical side bands, L17 should be unscrewed all the way up instead of peaked for maximum drive. Adjusting by this method cures the VFO FMing during modulation. (https://wireless-girl.com/Projects/AMTransmitters)/JohnsonVFOresistor.html)

I too would advise looking at W8JI's (https://www.w8ji.com/johnson_vfo_chirp_jump.htm) post on VFO feedback problems.   I did this mod on both my Ranger and Valiant and found it helpful.