[R-390] R390A 2nd LO subchassis oscillator issues

[Roger Ruszkowski]

Alan,
 
you wrote
----------------
poor sensitivity on some bands and quite fine on others.
----------------
therefore logically injection levels are fine. 
 
---------------
At 7 MHz third harmonic in not relevant.
When 7 Mhz third harmonic get relevant a different switch position and trimmer cap will take care of that.
 
7 Mhz is the top of the 4-7 octave. RF deck needs alignment
15 Mhz is top of 8-15 octave. The next set of RF transformers also need alignment.

Alan, it just may be time to give the whole receiver a good general maintenance service.
Thus clean up a whole slew of small problems that amount to dirt, oxidation, a few noisy tubes,
a few weak tubes and some general electrical alignment needed from aging parts.

Think about 8 hours on a Saturday and Sunday. Start with a nice where you can
take the receiver outside and give it a bath. 
Just mix the receiver in with family pets for the bath process.
After it dries out in the sun you can reassemble it and get on with the electrical stuff.

Roger AI4NI 
 
 
 
-----Original Message-----
From: Alan Victor <amvictor at ncsu.edu>
To: r-390 <r-390 at mailman.qth.net>
Sent: Sat, Sep 20, 2014 5:59 pm
Subject: [R-390] R390A 2nd LO subchassis oscillator issues


Good day. Have an R390A with poor sensitivity on some bands and quite fine
on others. Cam alignment and PTO run out look good. 17 MHz xtal running
well with 7-9 V p-p RF output at the injection port to the 1st mixer.
However, on 7 MHz, the required 3rd harmonic is way down in level and the 7
MHz sensitivity is hard hit. However, on 15 and 24 MHz poor sensitivity but
not nearly what it is on 7 MHz. Meanwhile on 21 MHz, better than 0.15 uV !
So I am suspecting a very aged low activity 9 MHz xtal and probably a dirty
bandswitch in the 2nd LO subchassis as well. As far as I can tell the
mechancial line up looks reasonable but the RF-electrical issues are
clearly more evident. Before I attempt to do any mechnaical alignment, I
think it makes sense to fix the OBVIOUS electrical shortcomings, like low
LO INJECTION level on the 2nd LO subchassis. Any ideas ? Tnx, Alan W4AMV.
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