R-390A Specifications for Z503
					Jacques Fortin, Oct 12, 2023

Jacques and I have been collaborating on a two level gain control for the AGC amp in the R-390A's.  
During our communications, we were concerned about the affect of too much or increased current 
through Z503.  He remembered not being able to find the specs on it, so he measured them and sent 
them to me to preserve and make easily available to all 390 folks.  He believes it is the same 
tank in the R-390.  I've attached his note, but here's the net of it:

C563= 82pF, Ceramic, 2%, 500V (dogbone shaped)
L514= ~ 1.5mH (1.492mH), 13.15 ohms winding resistance.
Bandpass: 442kHz and 468kHz at -3dB points.
BW= ~26kHz, Q= ~17.5
Impedance at 455kHz: ~4k ohms

Larry Haney, 10-15-2023

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Date: Oct 12, 2023 at 7:40 AM 
From: Jacques Fortin

And, as we are there: it is about the Z503.

I know that this is a component that was reported to fail many times.
I procured two spare Z503 to members of the R-390 group asking for some replacements.
I once searched into all the published R-390A documentation about the internal values (capacitor 
and inductance) of the Z503, but found nothing.
However, the inspections + measurements I made on a good sample (from a 1958 Moto IF deck) years 
ago gave me the following values:
C563= 82pF, Ceramic, 2%, 500V (dogbone shaped)
L514= ~ 1.5mH (1.492mH if the 82pF is exact), 13.15 ohms winding resistance.
Measured bandpass with a 100k ohms in series with the generator: 442kHz and 468kHz at -3dB points.
BW ~26kHz, Q= ~17.5
Impedance at 455kHz: ~4k ohms (mainly due to the coil internal resistance).

And btw, the Z-503 in a R-390 deck looks to be the same and the 82pF is correctly shown in the 
schematics.
I believe that it worth to be written in a document and put in the R-390 website.
Replacing a failed Z503 with anything on hand that resonates at 455kHz can change the gain of the 
AGC amplifier.

73, Jacques, VE2JFE in Montreal