Looking for info on construction of coils for sw3 receiver

awoodeye · **Joined:** Jan Wed 13, 2021 4:24 pm **Posts:** 5

I have all the winding information for the bandspread coils, BUT i can not find the details as to the wiring inside the coil for the GRID LEAK RESISTOR, TRIMMER CAPACITOR, OR GRID LEAD TERMINAL CONNECTION POINT.

The coils have 3 windings, plus the above components, and I do not know how to attach them, does anyone have a schematic of the coil itself, and any photos of the coil internals?

I am also interested in obtaining additional ham band coils for the sw3 receiver.

Thank you in advance, Woody N4MQ :?:

Radioroslyn · **Posted:** Jan Wed 13, 2021 9:32 pm

https://bama.edebris.com/download/natio ... /dcsw3.pdf

Terry N3GTE

awoodeye · **Joined:** Jan Wed 13, 2021 4:24 pm **Posts:** 5

I appreciate the link but that is for the dc radio, I am working with a model 2 with 6d6 and 76 tubes. They evidently have a grid leak resistor in their coils and a trimmer cap. I see that the grid connection is to the top of the coil which is helpful to know. Ill have to keep searching. thanks Woody :cry:

Chas · **Posted:** Jan Wed 13, 2021 11:44 pm

awoodeye wrote:

I appreciate the link but that is for the dc radio, I am working with a model 2 with 6d6 and 76 tubes. They evidently have a grid leak resistor in their coils and a trimmer cap. I see that the grid connection is to the top of the coil which is helpful to know. Ill have to keep searching. thanks Woody :cry:

Coils with grid cap/leak are bandspread. All coils for all series have same antenna and tuning turns only difference is the number of tickler turns. The latest tube type will have the newest turns so shooting for excess turns then remove to gain control of the regeneration.

The original forms and past replica forms are no longer available and will have to be hand made. The socket is not standard 6-pin.

The correct tube type will be stamped on the tube socket.

For the SW-3/5 collectors, someone could do a great service to the collecting community in aggregating all the known data and quirks.

YMMV chas wa1jfd Sw-3, DCsw-3, SW-5...

jim rozen · **Posted:** Jan Thu 14, 2021 12:56 am

At one time I posted the mechanical design drawings for SW-3 coils. Suggest that be included.

Also I found regulating the B+ did improve the regeneration stability. Tried it both ways, I did.

Chas · **Posted:** Jan Thu 14, 2021 1:14 am

Do you have a power supply for the radio?

awoodeye · **Joined:** Jan Wed 13, 2021 4:24 pm **Posts:** 5

wELL THE DATA IS COMING IN, THE COIL DETAIL IS REALLY INTERESTING. Caps lock..... Ok well the coil data is great, I have one bandpass coil in the mail and I intend on opening it to detail the connections and grid leak attachment point, amazing radio to hold so much interest 8 decades or so later. Thanks again to all. W :lol:

D Y

Chas · **Posted:** Jan Thu 14, 2021 2:10 am

awoodeye wrote:

wELL THE DATA IS COMING IN, THE COIL DETAIL IS REALLY INTERESTING. Caps lock..... Ok well the coil data is great, I have one bandpass coil in the mail and I intend on opening it to detail the connections and grid leak attachment point, amazing radio to hold so much interest 8 decades or so later. Thanks again to all. W :lol:

D Y

The critical coupling cap is INSIDE the 101 auto-former coil box, potted in tar....

Bandspread coil, if your stuck, PM and I will improve the document..

Sometimes there is failure of the co-axial coupling wire that is inside of the tuning condenser shaft. If it is failing the tuning will be erratic with noise. That cap inside the 101 can leaks too much it will cause excessive plate current in the amp along with distortion.

Do not aggressively clean the regeneration control potentiometer. The OEM pot has a carbon track that is dissolved with most solvent cleaners, Oops :roll:

YMMV chas wa1jfd

awoodeye · **Joined:** Jan Wed 13, 2021 4:24 pm **Posts:** 5

I found this from a friend, it answers the question finally. hope the link show up, Woody :lol:

https://mail.google.com/mail/u/0?ui=2&i ... &disp=safe

dtvmcdonald · **Posted:** Jan Thu 14, 2021 3:42 pm

awoodeye wrote:

I found this from a friend, it answers the question finally. hope the link show up, Woody :lol:

https://mail.google.com/mail/u/0?ui=2&i ... &disp=safe

Link fails. Its Google.

Chas · **Posted:** Jan Thu 14, 2021 3:43 pm

awoodeye wrote:

I found this from a friend, it answers the question finally. hope the link show up, Woody :lol:

https://mail.google.com/mail/u/0?ui=2&i ... &disp=safe

Sorry, I do not have a Google account, nor do I login to Google for any purpose... chas

awoodeye · **Joined:** Jan Wed 13, 2021 4:24 pm **Posts:** 5

How do I do that , what format? Woody

Chas · **Posted:** Jan Thu 14, 2021 5:25 pm

awoodeye wrote:

How do I do that , what format? Woody

The ARF can post TXT, and PDF JPG and PNG... chas

Greg G · **Posted:** Jan Thu 14, 2021 9:12 pm

This isn't anonymous. I authored it many years ago.

Greg Gore
WA1KBQ

anonymous wrote:

SW-3 coils were available for general coverage from 10 meters to 50KC's and amateur bandspread 10M through 160M. There were primarily three different coil versions produced by National during the years of SW-3 production designed to complement whatever tubes were employed in the different receivers over the years.

- Earliest coils were called the 10-20 series and were designed to work with receivers employing type 235 screen-grid tubes, they have paint dot color codes to identify tuning ranges.

- Next in the chronology was the 60-70 series coils which were designed to be optimal for the newer type 58 and 6D6 pentodes.

- The final version was called the 30-40 series which were designed for the metal octal equipped Universal SW-3 National continued to sell for a while after the war I think. 60-70 and 30-40 series coils have an identifying number stamped in the end between the pins to denote tuning range. With the exception of bandspread coils and very low frequency longwave coils Detector and RF coils are interchangeable. Detector coils have a capacitor mounted inside.

In truth SW-3 coils among the three series are interchangeable with the only difference being a small amount of antenna coupling and the degree of control rotation required to cause the detector to spill over into regeneration. National removed a winding turn from the tickler whenever RCA introduced a newer better tube with more gain to maintain spill over at the center of control rotation more or less. James Millen understood marketing and National sold a lot of coils.

Chas · **Posted:** Jan Fri 15, 2021 1:36 am

Thanks Greg... chas

jim rozen · **Posted:** Jan Fri 15, 2021 7:03 pm

SW3 coil drawing was there, then went away?

For those who want to build their own:

Radioroslyn · **Posted:** Jan Sat 16, 2021 3:26 am

I was looking around for coil forms and found a fellow on ebay that makes them and sells. He didn't have any for sale at the moment so I dropped him a note and this was the reply:

fxpel Top Rated Seller(19,321YellowShooting Star)

I used to make them but very bad rheumatoid arthritis has prevented me from doing so. They require me to use
my lathe which can often be difficult on my hands. I have several customers looking for them so I do plan on building them
but probably not until next month. I am getting over covid right now and that sent me for a loop.
I will keep your email aside and let you know when they are ready. They will be listed on Ebay.
Regards,
Frank

I'm sure I've purchased some from him before some years ago and he more than likely was the source for Ocean State Electronics years back. The quality is good and socket fit is good also. Have used a dozen or more and have been pleased with results. Pricing is about $15 ea.

He's out of the office for now till the 20th.

Terry

Looking for info on construction of coils for sw3 receiver

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