[R-390] LONG: Alignment, Overload and Distortion

Bill Hawkins [email protected]
Sun, 10 Mar 2002 15:41:02 -0600


Hope you are getting some good suggestions, but in case we're
all waiting for someone else to step in, I'll make a basic
suggestion:

Have you set the IF Gain pot on the IF Amp Assy? The Navy
manual says to change the RF cabling so that the IF Out jack
is connected to IF In on the IF Amp. Supply 150 microvolts
at 455 KC, 30% mod to the external IF Out jack. Set Function to
MGC and RF Gain to 10. Adjust IF Gain for -7 VDC at the Diode
Load terminal, not the AGC voltage. See the Manual for further
details.

Since the RF Deck has only one stage of gain (the other tubes
are oscillators and mixers) it seems unlikely that the IF Amp
would see as much as 10 millivolts input, but I don't know the
design input range. Perhaps the Technical Report has it.

Usually, distortion comes from clipping, which can be from core
saturation. In the 390A, it can also come from overdriving
the mechanical filters.

Does anyone know the design input range for the IF Amp?

Regards,
Bill Hawkins