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Author Topic: CW Transmitter oddity.  (Read 2589 times)
KC2VDM
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Posts: 145




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« on: March 01, 2013, 07:24:06 PM »

I fired up my Johnson Viking Adventurer today (After just having it sit around for a while) to try out a few new crystals. The CW note didn't sound that good. It seemed like the power supply became suddenly unfiltered. Kind of a choppy note.

I took the rig downstairs, redid a few "ok" solder joints, and while I was at it, I replaced the botched meter a previous OM put in. I tried the radio without its case, and the note sounded great. Tried a few more crystals without a problem. Then I put the case back in, and the bad sounding note came back. I made sure nothing was shorting out, and everything looks fine.

I'm not sure what could be causing it.
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N6GND
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Posts: 338




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« Reply #1 on: March 01, 2013, 08:13:30 PM »

I started out in 1956 with an Adventurer I put together with my 12 year-old-hands. I never got a report of a bad note on CW.

Got that bit of nostalgia off my chest.

I wonder what you mean by a "choppy note." I wonder exactly how you are monitoring your CW. This information could be useful for problem analysis and for keeping the nostalgia going.
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KD0REQ
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Posts: 858




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« Reply #2 on: March 02, 2013, 12:15:27 PM »

creepy case ground, maybe?
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KC2VDM
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Posts: 145




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« Reply #3 on: March 02, 2013, 02:01:25 PM »

The note sounds beautiful without the case on, but with the case, instead of a clean, solid note, its sounds choppy-kinda unfiltered.
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K8AXW
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Posts: 3685




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« Reply #4 on: March 02, 2013, 05:12:31 PM »

My first thought would be a long screw that is touching something inside the chassis. Even if the screws are original it's possible that your predecessor has either added or moved components that a case screw is touching.

Since I have no idea how your monitoring your "note" can I take a stab in the dark and consider the bad note as being a mechanical problem?  (Translated: Cabinet buzz)

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WB6BYU
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Posts: 13039




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« Reply #5 on: March 05, 2013, 12:38:19 PM »

Much will depend on the details of what you are calling a "choppy" note.

I don't have an Adventurer handy to look at, but some ideas:

1) it is possible that the presence of the cabinet affects the level of feedback
in the oscillator circuit by affecting the stray capacitance to ground, etc.
This might cause "squegging" or slow starting of the oscillator.  Some of the
older oscillator circuits depended on stray capacitance of the circuit and/or
tube to set the feedback.

2)  There might be an accidental grounding somewhere, either due to the
chassis screws sticking in too far. Or adding the case might cause some
other stage to oscillate.  (I had a great homebrew A2 transmitter when I put
enough capacitance across the VR tube and it oscillated.)

3)  There may be some piece of cable or wire that has an intermittent
connection and has to be bent out of the way to get the case on.  The
type of thing that works fine when the cable is straight, but acts up on
occasion when it is bent.


An oscillation in the VR tube will give you an AM modulated output.  The
oscillator "squegging" will give you a rough note as the oscillator starts,
overloads itself due to too much feedback, nearly drops out, then starts
back up again.
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