[R-390] If alignment and low signal

[Flowertime01 at wmconnect.com]

MICHAEL,    

Your working on a 1950 era receiver. 455 on your counter today is not the 
center of the filters.

The wisdom is to drive 455 from the generator in the 455 crystal on the .1 
band width.

Put the 455 into E211 on the Rf deck. hang the DC voltmeter on the diode load.

Rock the signal generator for maximum meter reading on the diode load with 
the band switch in the .1 position. That crystal under the Z501 transformer 
cover is your IF center frequency. If this frequency is within 1Mhz of the 455Khz 
you are OK. never mind those digital numbers displayed on test equipment. If 
they agree its just chance.

You cannot move the filter center frequency by adjusting the caps. Some 
Fellows did some test last year and find the caps just match the impedance and 
provide more signal pass with better matching. The filter centers are not exact.

The 455 crystal is within the 2Khz band pass. The 2Khz is within the 4Khz 
band pass and so on up the scale. They could all lay off to one side of  455 by 
8Khz. ( I have never seen a receiver that bad but it would be in spec if it 
did.)

You zero the BFO against the signal through the .1 crystal filter.

Once you get the signal generator centered into the crystal you leave it set 
and trim the caps on the mechanical filters for maximum signal out.

Barry - N4BUQ said,

You should see two peaks with the trimmers and if you 
don't, the SM caps are either bad or need a different value to make the 
trimmers peak in their ranges.

The trimmer caps can be cleaned. The back clip slips off and the top comes 
off.
You may have to unsolder the lead wire to get the back clip to slip off 
depending on lead length.

I echo Barry, Good luck

Roger L. Ruszkowski AI4NI


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