[R-390] Filters

[Craig Heaton]

Doug,

Something more than the Fluke will be needed to test C551, more to the point
it has to be tested at rated voltage. In this case 500V. Both of the
R-390/A's in my shack have had C551 replaced, their insulation resistance
was zip, nada, zero. The Sprague TO-6A analyzer showed the value (2MF) was
close but failed on IR. A new cap can be placed under the chassis; NTE makes
a mylar cap which will fit inside old can.

Craig,
____________________________________________________________________________
____________________________________________________________________________
___________ 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of quartz55
Sent: Monday, February 04, 2013 6:24 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Filters

Doug,

Well, I'm pretty sure the AGC problem in the one IF strip is confined to the
IF since the other IF unit seems to work pretty good AGC wise, but I do
still need to check the AGC action even on the 'good' IF strip.  I see
there's a test for AGC action in the book, I just need to go through it. 
But even the good AGC one has the 'gain drift' problem, so I'm not home free
on that one yet either.  I suppose I should fix the drift problem first and
then go on to the one with the bad filters and no AGC.

I'll check the AGC action tomorrow and see if I can get a feeling for where
the gain drift is coming from.  It will start off with 150uV 455KHz into the
IF module giving -7V on the diode load, then it 'snaps' and then 25-30uV
will give -7V, then it starts drifting around on the diode load meter
finally resting back at about 150uV in a half an hour or so.  Since it takes
so long to do this, it's hard to check.  The 2uF C551 checks out OK on the
Fluke, if a bit high, but who knows what it's doing during warm up.  I need
to start checking voltages as it warms up.  This may take a while.  I do
have some tube extenders.  Other problem is one of the pins on P112 is
broken, keeps falling off and now I've lost it, I need a new P112 for that
one unless I can swap the line to the unused pin, but then the IF modules
are not compatable.

Yes, that AGC stuff is pretty iffy to check since so many things are hooked
to it.

I hope I'm responding to this group correctly, I notice I can't just
'reply'.

BTW Tisha, thanks for the link to this group.  I see you are on Lookout Mt,
but I was thinking of the one at Chatanooga, I've been there for work
(repeater up there), but it's a different Mt in a different state.


______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html