[R-390] R-390 Question

[David C. Hallam]

I get about 40% of full scale with the calibrator signal.

Something you said about cathode grounds started me thinking.  I checked the
RF gain pot.  The schematic calls out 25K ohm and I just measured mine at 6K
ohm.  Don't know if that has anything to do with my loss of sensitivity
problem since in AGC you operate at max gain, but I will replace it.

David
KC2JD

-----Original Message-----
From: Tim Shoppa [mailto:tshoppa at wmata.com]
Sent: Tuesday, September 05, 2006 2:27 PM
To: r-390 at mailman.qth.net; dhallam at rapidsys.com
Subject: RE: [R-390] R-390 Question


>   0.2 ohm might be the resistance of the filament transformer, but
> when you take the reading, there are 4 series strings of tube
filaments with
> some series resistance in a couple of them in parallel with the
transformer.

The DC resistance of the filament transformer will dominate, of course.

> I think that's why the manual gives normal readings in the range of 6
to 9.5
> ohm.  Could be an error in the manual though.  That's not unknown.

Maybe there's an "assumed" step of 0: uncable the PS module? It is
almost impossible for there to be a solid short across the filament
transformer,
something would blow! (And not necessarily the fuse!)

> The reason I got into all of this is that the receiver lost
sensitivity and
> had no carrier level meter movement.  What is an expected carrier
level
> meter reading for the calibrator on say 15MHz?  I could just barely
hear 15
> MHz WWV while on my 75S-3 WWV was coming in way over S9 and I could
also
> hear WWVH.

On my 390A the calibrator will deflect the carrier level meter 3/4 of
the way on most bands. HAve no idea how relevant this is to your 390!

Tim.