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THE AM BULLETIN BOARD => Technical Forum => Topic started by: W7SOE on December 21, 2016, 01:21:29 PM



Title: SX-28 Band Switch
Post by: W7SOE on December 21, 2016, 01:21:29 PM
Hi
I am confused, trying to correlate the SX-28 schematic to what I see in the first RF section.  My radio has two wafer switches in the first RF section.  I find images from other SX-28s where there appear to be three.
I found the "old" SX-28 schematic on BAMA (Mine is a 1941 model).  I thought that it was a match except that it shows trimmer caps in the first RF section where mine has none.

I have attached a picture of mine here.

Thanks for the help.

Rich


Title: Re: SX-28 Band Switch
Post by: W7SOE on December 21, 2016, 01:22:48 PM
Here is the same section with a different arrangement, from a later model I presume...

Rich


Title: Re: SX-28 Band Switch
Post by: W7SOE on December 21, 2016, 02:18:28 PM
I have found an answer from this website:
http://www.radioblvd.com/SX28Notes.html



1st RF coils have trimmers (Bands 3-6) - This was probably a schematic error although trimmers are shown on 1940 and 1941 versions. Even the earliest manual's photo of the chassis underside show that no trimmers were used on these four coils.



Title: Re: SX-28 Band Switch
Post by: KB2WIG on December 21, 2016, 02:51:52 PM


R

Good luck with your '28. They are wonder full machines, er, radios.  I listen to 740 kc, CFZM on a big old stereo speaker. The audio is excellent fer da oldies.

Take plenty of pictures and wiring diagrams. When I rebuilt mine, everything worked fine. Except I had this little, little brass washer that goes onto the band switch, left over. If you would take a photo of where it is on yours, I would be very happy. ( if there is one at all) Also, don't make a mistake when re inserting the shaft into the radio. I squashed part of the phenolic on one of the band switch  wafers.....


klc


Title: Re: SX-28 Band Switch
Post by: W7SOE on December 22, 2016, 01:05:31 PM
I don't see a brass washer except a rather thick one between the circlip and the outer retaining plate, if that makes sense.

Rich


Title: Re: SX-28 Band Switch
Post by: KB2WIG on December 23, 2016, 12:08:14 PM


R,

Thanks fer looking.  The 'washer' on my '28 is very thin. It somewhere between the thickness of a post it note and a index card, closer to the index card.... After I replaced most of the components in the '28 I went out and purchased an digi camera..... This was about 10 years or so ago.


klc


Title: Re: SX-28 Band Switch
Post by: W6MQI on December 27, 2016, 09:21:24 PM
Hi Rich,
 Good luck on your SX-28 restoration I did mine about four years ago a complete over haul all new caps, and resistors lots of work. Looks like we may have the same model 28 mine is a non A version pre war.

73, Dave
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands