[R-390] RE: Mechanical filter repair

[Dennis Pharr]

Will do Steve.  Actually, I've been looking at several alternatives in the
ceramic Filter/resonator line.  One other choice suggested by Les Locklear
is: 

http://www.kiwa.com/kiwa455.html  

These appear to be ceramic filters with a solid-state preamp to overcome the
slight insertion loss.  Also, they come pre-packaged so they might be easier
to install.  However, my plan was to gut the existing mechanical filter
housing and insert the ceramic.  But, of course, I would breadboard the
thing first to make sure it works before destroying the already defunct
filter.

>From everything I've read the mechanical filters in the R390A exhibit a 25db
loss.  The 6BA6 stage following the filters makes up this loss.  So, since
the ceramic filters want to see a low impedance source and load, I would
think it would be relatively easy to design an attenuation/impedance
matching network for each end of the filter.  This would insure that the
filter 'sees' the driving and load impedances it wants and also that the
455kc RF levels seen by the following 6BA6 stage are closely matched to the
output level of the other filters.

I have found one interesting product by Toko in the Digikey catalog:

http://dkc3.digikey.com/PDF/T042/0701.pdf
http://www.tokoam.com/passives/filters/ceramic/pdf/cfm2.pdf

Also, here's an interesting tidbit - in the R390A-Y2K-Release-1.pdf manual
on page 3-16 under the NOTES at the bottom of the page it states:

3. R-390A/URR MFG by EAC Serial No. 1 thru 460 have ceramic filters. Replace
with mechanical filters when ceramic type are defective.

Apparently, the early EAC's had ceramic filters.  So, I guess it can be
done.

73
Dennis
WD5JWY





-----Original Message-----
From: Steve Hobensack [mailto:stevehobensack at hotmail.com] 
Sent: Thursday, August 19, 2004 5:55 PM
To: r-390 at mailman.qth.net
Cc: dpharr53 at swbell.net
Subject: RE: Mechanical filter repair

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Dennis, If you figure out how to match those Toko or Murata filters,
post it on it on the net. Maybe a tech from those companies or Kiwa
will know how to install them in Collins tube rigs. I know the
filters limit bandwidth to 3 khz on my Sony 2010, and work well. As I
remember, the speck sheet that comes with those filters shows typical
installations only on transistor circuits.
73...Steve...KJ8L




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