[R-390] R390/A T401

[Flowertime01 at wmconnect.com]

Richard,

Does anyone have an alignment process for the tunable inductor T401 in an 
R-390A XTAL oscillator ?
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Very good question.

R390/A TM11-5820-358-35 Para 74 omits this subject. More than once we tried 
to get it into a new edition of the TM. (1968 - 1975)

R390 TM11-5820-357-35 Para 77 give a procedure to do the alignment in the 
R390. We just used this procedure on the R390/A. 

I do not have my Y2K manual on this computer to see if the subject is covered.

>From the R390 TM.

Hang a Neg DC voltmeter into E210 grid test point of second mixer.


Set the slug of T401 at about 1/4 out from all the way in.
Set the receiver to 31 Meg.
Get a tweeker on the 31 meg trim cap in the osc deck.
Get a tweeker on T401.
Get the Voltmeter scale readable.
Spin the cap around.
It should peak twice.
Turn T401 out.
Spin the cap around.
It should peak twice.

Repeat 
Turn T401 out.
Spin the cap around.
It should peak twice.

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Or
Find the point of the trim cap between the two peaks. (max cap)
Adjust T401 out until the meter peaks)
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At some point the cap it will only peak once. (max cap but not enough cap)

Now set the trimmer cap off peak a bit and reset T401 for max reading.
---Adjust T401 back in.

This should leave T401 peaked for best response.

You should get two peaks on the cap again.


Some times you will have a weak crystal or harmonic of the crystal.
Then you may do this process on that frequency with that trimmer cap to bring 
the weak 1Mhz band up as best you can. Then retrim all the caps to T401 as 
adjusted for the poorest crystal in the osc deck.

If the poor crystal will not let you trim it up and get every thing else to 
pass, then it is time to change that crystal. This process being used to judge 
when its time to call a crystal bad.

If you have a band that does not peak twice with the trimmer cap, this is a 
band worth trying to reset T401 for higher output. You may have several 
crystals that need to have the socket cleaned or the crystal replaced. 

Adding small caps to bring a trimmer up to peak twice with T401 can be more 
work than finding a different crystal that will work.

Roger Ruszkowski AI4NI