[R-390] AGC Problems

[Flowertime01 at wmconnect.com]

In a message dated 7/14/05 8:10:24 AM Eastern Daylight Time, 
JMILLER1706 at cfl.rr.com writes:

There is supposed to be a jumper on the rear panel termial strip for a 
remote AGC line?  What would happen if it was missing?

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In the R390/A, V201 the RF amp has a R234 a 1.5 meg resistor on the AGC line 
to ground. So with no jumper this resistor completes the circuit path for the 
AGC line on the tubes that have AGC on the control grid.

In MGC where the AGC line is shorted, there are other resistors in the AGC 
line between the grids and the short point on the function switch. There will be 
a small loss of receiver gain in MGC with the jumper missing. You likely may 
not even be able to hear the difference between jumper and no jumper with the 
function switch set to MGC.

In AGC, no AGC voltage is feed back to any thing, The AGC and MGC positions 
on the function switch will act exactly alike to you. The carrier meter will 
peg over when switching AGC time constants because all that circuit is before 
the back panel jumper. The audio will not be lost like normal however when 
changing the AGC time constant, because the AGC charging time, when switched, is 
not being carried over the jumper and applied to the tubes.

If you did not know, you could run the receiver for years with the AGC jumper 
missing and never miss a thing. As much as the receivers AGC performance has 
been cried about, you may think your receiver is just normal.

Roger KC6TRU