[Boatanchors] F455FA21 and F455FB21 difference

[Gary Schafer]

I thought I recognized that number. The "B" was made during the 60's as a
less expensive filter to the FA series. Essentially the same filter except
the FB was less expensive, aimed at the amateur market. I think that the
specs were a little looser than the FA filter.

I think that the chart referenced may be wrong on the FB filter. As I recall
the nose was the same as the FA (2.1 KHz) but the skirt was a little wider
on the B. I would have to look at the spec sheet if I could ever find it. 
Somewhere around here I have an original spec sheet on the F455FB21 filter.


Not sure about the FB being used in the SBE34 or the SBE33. I know that the
FA was used in the SBE33 as I replaced a couple years ago. They may have
gone to the FB in the SBE34 but I don't think so.


On either filter be careful of how much current and signal you put on the
coils. They can be burned out with an ohmmeter! 

In the SBE33 they ran transistor collector current thru the filter coil.
When the transistor decided to short it took out the filter!

I modified the SBE33 to feed the collector with a choke and capacitive
coupled the collector to the filter coil so no current ever was on the coil.

The transistors used in that radio were germainium and would easily be
destroyed.

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of GRANT YOUNGMAN
> Sent: Thursday, March 05, 2015 8:33 PM
> To: boatanchors
> Subject: Re: [Boatanchors] F455FA21 and F455FB21 difference
> 
> There is information specific to the FB-series filter on this page:
> 
> http://www.angelfire.com/de/vk3kcm/filters.html
> 
> Scroll down to near the bottom.
> 
> Grant NQ5T
> 
> 
> 
> > On Mar 5, 2015, at 7:53 PM, HL1FB <yonglee at yonsei.ac.kr> wrote:
> >
> > Thanks for all the responses. Nothing is concrete.
> >
> > I have both filters. They are exactly the same dimensions.
> >
> > And measures the same in my IFR1600 traxcking generator.
> >
> > Collins tube radios use FA type and some solid state radios like
> >
> > the old SBE34 use FB type.
> >
> > So I guess only impedance is different but not certain.
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