Drake 2B – working again

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Posted by w0ep on October 24, 2018 at 8:22 pm

[Today’s run:  3.4 ]

Like a lot of my projects, about 80% is working up the motivation and the idea about how to do the thing.  That’s the problem with being a perpetual amateur:  I don’t do these things often enough to get a professional type frame of mind and angle of attack.

I did read the troubleshooting information in the manual I downloaded.  That helped.They outline a general back-to-front attack:  start with the audio output and work back toward the front end where the antenna connection is.  I injected an audio signal and that came out.  Then I was a bit confused as to whether the audio driver was working correctly or not.  I sat on it for awhile.

Yesterday I decided to check the various oscillators to see if they were working.  The manual talks about using a receiver to listen for them, so I did that.  The front end crystal oscillators and the VFO appeared to be working.   I had a length of coax and I attached a little coiled wire with some clip leads and I moved the coiled wire around.  I used my SDRplay and I could see everything on the spectrum/waterfall display.

I got to a stage where there is a 405 kHz oscillator which mixes down 455 kHz to 50 kHz.  And I could not find the 405 kHz signal. There is an oscillator in the grid/cathode circuit which had 2 resistors, 2 capacitors and a canned coil.   I put my little loop over the top of the oscillator tube and.. nothing.   I tried to measure the component values and everything seemed to measure OK.  But I still couldn’t get any sign of the 405 kHz signal.  Swapped tubes, tried everything.

So I ended up taking that canned coil and the attached components out.  I detached the components and measured them.  I measured the coil.  Everything looked good.  I put it all back together and put it back in.  And the 405 kHz oscillator is back larger than life.  I had to adjust the coil a bit, easy as can be.  Now the radio is playing like it never had a problem.  Maybe it was a cold solder joint or something, I don’t know.

I’m going to let it play this afternoon then maybe I will run through the “tune up” procedure this evening and peak all of the IF cans and such.


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