[R-390] RE: Mechanical filter repair

[Bob Camp]

Hi

The early EAC's did indeed have ceramic filters in them. Of course they 
were designed to match tube input and output impedances. Needless to 
say that made them very different parts than the ceramic filters you 
can buy today.

If you are going shopping for filters be careful to check out both the 
skirt selectivity and the ultimate attenuation numbers. It would be a 
shame to go to all the work of matching them into the radio and find 
out that the selectivity of the radio had been degraded. IF filters are 
*very* sensitive to matching impedances so it will be a fair amount of 
work to get it right ....

There is a note in one of the Collins reports on the R-390A that 
suggests the original requirement for the ultimate selectivity of the 
radio was not met in the final design. There is no further elaboration 
on exactly what the issue was. If they are referring to an IF issue 
then there may not be a whole lot of extra margin on the filter chain.

	Take Care!

		Bob Camp
		KB8TQ


On Aug 19, 2004, at 11:44 PM, Dennis Pharr wrote:

> 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
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> 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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