Bc-1000 / SCR-300 schematic from TM11-4024 & TM-11-637

[YLG80]

Here is a seldom found schematic of the BC-1000.
It's attached to the TM11-4024 "BC-1000-A and -B REPAIR INSTRUCTIONS" back cover page.(Aug 1945)
http://www.avi-plus.com/download/BC-100 ... TIC-A3.pdf
The pdf is in A3 format.

Yves

[Radtech]

There are schematics in each of the SCR300 tech manuals.

[YLG80]

Yes, I know.
But the one in TM11-4024 has been redrawn differently and is printed on a long folded paper strip.

[YLG80]

Here is the schematic scan as drawn in the TM-11-637 10/1944
http://www.avi-plus.com/download/SCHEMA ... _VRC-3.pdf
The pdf is in A3 format.
TM-11-637 and TM-11-242 schematic are identical. TM-11_4024 schematic is different.

The wires color legend is included and common plate (W-BL-TR) and grid (W-GN-TR) wiring colors are mentioned correctly.
That schematic incorporates only one of the mods made to improve BC-1000-A and B :
R41 is a 15K ohms instead of 22K as shown in TM-11-4024 shematic.
The mods on the squelch circuit are not integrated in both TM's schematics.

In TM-11-4024, the wire colors for V12 plate is incorrect and V7-V8 wire colors are missing although the wiring for V7 up to V14 plates is common.
In TM-11-4024, the power plug connection has an error : pin 4 and 7 should not be connected together.
Pin 4 is used to activate the vibrator PS.
However the plug PL-1 legend is correct !

[YLG80]

Here is a very nice and clear picture showing a tech repairing a BC-1000, in 1944 in Fort Benning.

1944_Ft_BENNING-Pvt Frank Obrien-.jpg (140.55 KiB) Viewed 2768 times

I've have exactly the same combination in front of me : BA-70 + BC-1000 and dummy antenna A-28.
My soldering iron is just of a much more modern type !
Trying to fix a TX problem.(no HF power)

[YLG80]

And a photo of his colleague Sgt Porterfield, taken the same day,
He has also an SCR-300 in front of him.

Sgt_J-D_Porterfield_Ft_Benning-1944_BC-1000_SCR-300-web.jpg (110.23 KiB) Viewed 2757 times

This tech has a typewriter in front of him, and the 437 pages HAM radio publication Radio News, Feb. 1944 issue, on the table at the right side.

Radio_News_Feb_1944-B-W.png (124.11 KiB) Viewed 2757 times

In that issue, there is an article on field tests made on FM radio's (SCR-300 and SCR-610) compared to AM radios, written by Major William S. Marks.
The new FM equipment details were still secret at that time.

In that Radio News issue, they are also talking about an FM radio used by the MP's in the UK during the war.

Does anyone know what type of radio it is ??

Jeep_MP_FM_radio.jpg (132.86 KiB) Viewed 2757 times

The radio

WWII_MP_FM_RADIO.jpg (129.39 KiB) Viewed 2757 times

[YLG80]

An interesting zipped pdf document regarding the SCR-300 / BC-1000 weather testing process during production in the Galvin Mfg. Corp. plant.
There are pictures of the Galvin plant test equipments
Page 1 of 2

SCR-300_WEATHER_TESTING_page_1.zip

(125.54 KiB) Downloaded 67 times

Page 2 of 2

SCR-300_WEATHER_TESTING_Page_2.zip

(140.44 KiB) Downloaded 47 times

[g504]

Hello.

This radio is a SCR-293.



g504

[YLG80]

Merci, thank you.
I've never heard about that radio before reading that article about MP radio's.
It looks like that radio was already existing before Pearl Harbor when the Signal Corps was still in discussions about the AM and FM modulations.
Yves

[g504]

Bonjour Yves.

Elle me manque dans ma collection et j'en cherche toujours une et complète.
Elle fonctionne uniquement en phonie, en modulation de fréquence.
La portée est de 25 kilomètres
Sa gamme de fréquences est de 20 à 27.9 mégacycles avec cinq fréquences préréglées.
Alimentation en 12 ou 24 volts.
Elle était destinée principalement aux chars.
Cordialement.

g504

[frenchman]

bonjour thierry
ha les radio c'est un trou sans fin comme l'histoire du poisson rouge que l'on achete sure la foire dans un
petit sac en plastic moi aussi j'aime les radios mais limite maintenant a ceux de la guerre d'idochine
plus petit et ca marche bien et plus facile a reparer
cordialement
frenchman claude

[g504]

Hello.

That is true.
Technology, in recent years, has really changed the history of radio.

g504

[Littlewood]

Wow amazing tech pics thank you for sharing, not often do you see the sets being repaired, I wonder what course these soldiers took to enable them to repair, I'm not tech but repairs all the sets I have inc. BC610 the manuals are excellent but it takes me a long time to troubleshoot. If only we could have a vintage repair course to go on, I would be 1st to sign up. thanks again and if you have more repair pics please post. James

[YLG80]

Hello James,
Waow, you have many radio's and generators.

You can find interesting information on that critical problem of training courses during the war here :
https://en.wikipedia.org/wiki/Electroni ... ng_Program

At the beginning of the war the US army has oriented most of the HAM radios towards the radio and electronics related activities.
But after a while, they found themselves short of resources and they had to start quick training courses.
The US army was helped in that effort by extraordinary good repair and troubleshooting manuals and by the good organization in echelons.
This helped to reduce the needs for very high skills.

Radio amateurs who were too young, too old or not able to serve in the military, including many women, were used in civilian assignments.
Woman testing a repaired radio in a repair shop:

NYA_working-in-radio-repair-shop-web.jpg (121.4 KiB) Viewed 2704 times

Here is a funny story on how the Signal Corps was hiring certain techs !

My father had a background in radio and electronics, and had been deeply involved in amateur radio from the 1920s through the 1930s.
When World War II began overseas, he was hired as a civilian employee of the Army Signal Corps.
His draft board considered him, young, single and healthy, as a prime candidate for the draft.
The Signal Corps instructed him to ignore his draft notice while the Signal Corps processed his papers for assignment to Aviation Cadet training as a non-flying officer, barely ahead of the appearance of FBI agents seeking to arrest him as a draft dodger.
When he completed his Aviation Cadet training, he was commissioned in the Air Corps and assigned as an instructor in the Air Corps' school for radio operators and radio mechanics.

Mobile repair truck with the "usual" SCR-536/BC-611 on the table !

Signal_Corps_radio_techs_in_repair_trucbw.jpg (53.04 KiB) Viewed 2704 times

Yves

[YLG80]

For James !
Radio class room in Italy in 1944.
Teletype on the front table.

Radio_Maintenance_class_Caserta_Italy-1944-01-18.jpg (81.11 KiB) Viewed 2689 times