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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 468 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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Michael

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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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