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Johnson Ranger VFO Drifts on 40/20




 
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Author Topic: Johnson Ranger VFO Drifts on 40/20  (Read 1812 times)
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W1TTL
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« on: November 25, 2021, 07:54:20 AM »

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


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W1NB
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« Reply #1 on: November 26, 2021, 08:03:27 PM »

Just a thought but in light of the change when putting pressure on the switch, possibly a poorly contacting wafer switch segment?
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W1TTL
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« Reply #2 on: November 26, 2021, 08:09:14 PM »

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
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N5RLR
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« Reply #3 on: November 27, 2021, 05:21:43 AM »

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.
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« Reply #4 on: November 29, 2021, 07:42:02 PM »

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
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« Reply #5 on: December 18, 2021, 10:47:02 AM »

try cleaning the grounding wipers on the tuning capacitor
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W1TTL
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« Reply #6 on: December 28, 2021, 05:20:04 PM »

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
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« Reply #7 on: January 05, 2022, 06:53:19 PM »

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.   
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Beefus

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W1TTL
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« Reply #8 on: January 05, 2022, 07:39:03 PM »

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
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KW4H
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« Reply #9 on: January 05, 2022, 10:40:41 PM »

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
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W1TTL
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« Reply #10 on: January 06, 2022, 06:09:01 PM »

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
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KW4H
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« Reply #11 on: January 06, 2022, 06:55:03 PM »

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
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W1TTL
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« Reply #12 on: January 06, 2022, 07:10:01 PM »

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
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KW4H
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« Reply #13 on: January 06, 2022, 08:54:20 PM »

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
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KW4H
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« Reply #14 on: January 06, 2022, 10:19:27 PM »

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
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KW4H
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« Reply #15 on: January 07, 2022, 08:49:40 AM »

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
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W1TTL
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« Reply #16 on: January 07, 2022, 04:12:30 PM »

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  
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KW4H
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« Reply #17 on: January 07, 2022, 05:38:47 PM »


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


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
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WD5JKO
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« Reply #18 on: January 08, 2022, 10:24:34 AM »


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
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W1TTL
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« Reply #19 on: January 08, 2022, 03:24:29 PM »

Jim,

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

73, Tony W1TTL
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