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 Post subject: National FBXA receiver
PostPosted: Apr Mon 29, 2019 2:12 am 
Member

Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1453
Location: Santa Rosa, CA
Yesterday was the onlyl ham junkfest left in the area and as usual
it was a lot of fun and a wide variety of things showed up.

Had planned to concentrate on selling but, well, I'm sure you
all know how that usually goes!

Ended up with a number of vintage receivers. One of which was a
National FBXA which is an FB-7 with a crystal filter. Attached to
the side of the FBXA with 1" stand offs was the carcas of what was
an SW3. From what I can see it had been converted to a preselector
for the FBXA. And poorly done. Both have been heavily modified, missing
parts, and in generally rough condition.

I've had very few older National receivers so little experience
with what is correct and what is not.

My question is does the FBXA have more than one control (horizontal
disc in upper right hand side panel)? Mine has this, which appears to
be factory but two other round knobs as well on the right side panel.

Yes, I've looked on the 'net but no clear pics of the right side panel
and only the disc control (xtal phasing?) is mentioned.
Steve W6SSP

ps- looking for SW3 parts if anyone has a junker, especially the volume
control and mounting hardware, also an original dial

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 Post subject: Re: National FBXA receiver
PostPosted: Apr Mon 29, 2019 4:48 pm 
Member

Joined: May Fri 01, 2015 2:33 am
Posts: 1339
Location: Roslyn,Pa 19001
Hi Steve
It might be helpful if you post a couple of pic of the SW-3 to see what you have and what you need. I'm not sure what you are trying to accomplish, restore the SW-3 or use it as a preselector for the FB-7. The bracket for the rf gain control is pretty simple to make. A piece of thin flat steel add four bends and your done. It's held on with 2 #6 screws and a couple of fiber washers. If you are interested I'll dig up the dimensions for you. The disk/knob I use to mold my own as they are hard to come by. No sure if my mold is still good it may gotten hard over the years.
The preselector might be in QST Aug '41 if it was done way back in the old days. If you don't have access to the article I can email it to you.

GL
Terry N3GTE


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 Post subject: Re: National FBXA receiver
PostPosted: Apr Mon 29, 2019 8:35 pm 
Member

Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1453
Location: Santa Rosa, CA
Hi Terry,
For now I'm concentrating on the FBXA (and a Comet Pro, HRO-5R
and HRO 1-10). The SW3 is missing so much it'll be a long term
project or even sold for parts. Pics are difficult as I do not
have high speed net access.

Sounds like you are familiar with the SW3, so here's what I have;
chassis, variable caps, tuning dial is there but the wrong one,
sockets, AF choke and the two round knobs and associated cap/rheostat.
Many under chassis r's and c's but badly hacked so will start
from scratch in this area. Cabinet has many extra holes where it was
attached to the FBXA. Making a bracket is no problem but since
I need the rheostat and knob I'm hoping the bracket will come with them.

No intention of using the SW3 as a preselector for the FBXA but would
like to restore each to as close to original as possible. Fixed up an SW3
for a friend recently so was hoping to get one for myself.
Steve

Thanks for the tip on the article, will look it up. Have most QST's here.
And it does look like this hack job was done in the 1940's based on the
parts used.
Steve

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 Post subject: Re: National FBXA receiver
PostPosted: Apr Mon 29, 2019 10:25 pm 
Member

Joined: May Fri 01, 2015 2:33 am
Posts: 1339
Location: Roslyn,Pa 19001
>For now I'm concentrating on the FBXA (and a Comet Pro, HRO-5R
and HRO 1-10).
My your a busy little bee!!
Have serviced a bunch of SW-3's and have a number of older National sets including a FB-7 and a couple of prewar HRO seniors. Even though the the 1-10 has a pw dial (that's the dial used or the HRO) it's not considered a HRO just a 1-10 or a 1-10A depending on what it was made.
You may want to have a look a 11-31 QST It's a great primer on how the SW-3 was designed and how it works.
It's somewhat important to figure which version your set started out as as the chassis is set up a little differently. Here's a few pics of an early chassis https://www.qsl.net/wa9wfa/sw3version1.htm and later https://www.qsl.net/wa9wfa/ha00007.htm These are AC sets there is 6v dc model and a 2v dc model along w/a universal model that can operate from batteries or an ac p/s.
CQ has a couple of articles on the subject in 7/71 and 2/78, does have a few mistakes.
It's not too uncommon for the two shields inside the cabinet to be removed, originally they where spot welled in place. I bit of a pain to fab and install. On the ac models there should be two mounting brackets for a voltage divider resistor. Sometimes they are snapped off when the set is modified.
Here's a drawing of the bracket. The pot is a 10K lin taper. Thought I had a spare but don't. Have some parts that eventually will a complete set.

Terry


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