[R-390] Filters

[Craig Heaton]

Another way to skin the cat:

After going thru the beast, replacing all of the offending BBOD's,
electrolytic caps, mechanical/electrical alignment, getting all sections up
to snuff, finding the best tubes in the correct places, etc: I pick the
filter that has the least voltage at the diode load, crank up the IF gain
till -7 volts is attained. 

Then if one wants the same gain on the rest of the filters & the trimmer
caps are in that IF section, adjust the other three down to -7 volts. 

Been there, done that. At times I just peak each filter for the max and pick
the filter I use the most and set the IF gain to -7 volts for that filter.
With the RFI in the neighborhood, weak signals are never heard & IF gain
adjustments are only an excuse for something to do on a rainy day in
Springtucky, Orygun. 

Craig,
----------------------------------------------------------------------------
----------------------------------------------------------------------------
-------------- 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of quartz55
Sent: Tuesday, February 05, 2013 9:52 AM
To: r-390 at mailman.qth.net
Subject: [R-390] Filters

Yes, the 2K filter does have some action through it, but gives -2V diode
load where the 8 and 16 give -7V, but the 4 appears dead.  I'll have to go
through the .1, 1 455 crystal to see if something in there is dragging down
the 2 filter.  The filters seem to check OK with the ohmmeter though.  I
don't think it's in the switch, everything looks to be original and
undisturbed unless the guy was really good.

The variable action I'm talking about is during a time period through the
same filter so I think it's a cap or something changing value during warm
up.  And that's in another unit.  The filters in it are good.

BTW I took L601 apart and it appears to be made with #34 enameled wire and
it smells really burned.  Lots of wax in the thing and the round button
popped off while I had the heat gun on it and I can't find it now.  Not sure
it's worth trying to re-wind if I can find a replacement at a reasonable
price.  110 ohms for #34 is over 400'.
______________________________________________________________
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