SCR-274-N Technical Manual Link and early P-47 radio questions!

[trysBennett2003]

Hello,

I just came across a 1943 Handbook Maintenance Instructions manual for the SCR-274-N radio set (used in p-47, among many others), that may be of use to some folks, if it hasn't been posted before! http://www.scr-274-n.info/to12r23scr2742.pdf

I found it off of SCR-274-N Links to other sites.

I was wondering if some folks knowledgeable in such things could answer a few radio-related questions for me about early model P-47's.

First off, I am trying to figure out the actual wire-paths for this radio set for an early P-47 D (-15-RE). The only illustration I have been able to find, with this actual radio in it, is the blurry illustration of the right-cockpit from the pilot's manual (p.20 in my copy). The MBI P-47 book has a painted version of this illustration, and I believe I have also found the source photograph that the illustration was based from, (I think it was in the Detail and Scale book), but all three illustrations are blurred and the wiring obscured by the t-30 microphone set looped over the command transmitter control box several times. I am also trying to figure out what the two seemingly-featureless boxes to the bottom-left of the crystal-selector switch are. It appears that the further-left box might have wiring running to the command receiver control box, but this doesn't make much sense according to the manual, and also appears to be the wrong direction from where the wires are twisting off of the command receiver control box itself. Not to mention the command receiver and transmitter, where the wires would logically connect, is located in the storage compartment aft of the cockpit. The only thing I've been able to find out for certain, is where to plug in the mic and where to plug in the headphones!

Secondly, in the manual I posted above, there seems to be no reference to a crystal selector switch, but I know the p-47 C\early D had one located left of the BC-450-A command control box. What did it link into? I notice two-jacks coming off of it in the illustration, one of which seems to go up into the sill, near the fluorescent panel light, the other seems to go into the unidentified box, bellow left of the crystal filter selector box. On the MBI painted-illustration, (which I don't really trust 100%), you can make out "voice and both" on the switch box, which makes sense with instructions in the pilot manual. Also in the MBI illustration, you can see what appears to be "switchbox BC-348" written. There is a radio-command control box called a BC-348 -- but it looks nothing like the example here. That one looks more like something on a B-17. I was wondering if anyone had a good, clear photograph of this crystal-selector box so i can verify what the text reads.



As far as I can tell, a similar radio setup was used in p-39D's, and P-40 series aircraft, as well as possibly the A-36\early mustangs, but without the crystal-select box. I also can't seem to find any sort of antenna relay control, so that is confusing as well.

Lastly, does anyone know what the DF loop on the back of some CBI p-47's was hooked into, and what sort of control box it had in the cockpit?

I'm afraid I'm one of those obsessive types when it comes to model airplanes...

Cheers!

[Micdrow]

Hi Bennett,

I dont have time tonight to look but might be able to point you in the right direction if you havent found this link. Go through the whole thread and you will find quite a few different model P-47 pilot manuals that you can down load. I believe if I remember right some of them will show pictures of the radio but dont remember for sure. Let me know if you have problems

http://www.ww2aircraft.net/forum/oth...al-s-5081.html

All the best
Paul

[trysBennett2003]

Thanks Paul!

Still can't find anything on it, but if I come accross the answer I'll be sure to post it!

[Higgshunter]

Hello,

I may be able to help you with the radio wiring diagram for the P-47D-15. Very early models of the P-47B use the SCR-287 rather that the SCR-274. PM me if you still need the information.

Bill

[aafradio]

I know this is an old thread, but it seems appropriate to close it out with some corrections and clarifications.

I am also trying to figure out what the two seemingly-featureless boxes to the bottom-left of the crystal-selector switch are. It appears that the further-left box might have wiring running to the command receiver control box, but this doesn't make much sense according to the manual, and also appears to be the wrong direction from where the wires are twisting off of the command receiver control box itself. Not to mention the command receiver and transmitter, where the wires would logically connect, is located in the storage compartment aft of the cockpit. The only thing I've been able to find out for certain, is where to plug in the mic and where to plug in the headphones!

The leftmost box is an FL-5 audio filter. See below for more on it. The right hand box appears to be a radio power switch or breaker mounted in a sheet metal enclosure. Basically a master power switch for comms.

Secondly, in the manual I posted above, there seems to be no reference to a crystal selector switch, but I know the p-47 C\early D had one located left of the BC-450-A command control box. What did it link into?....Also in the MBI illustration, you can see what appears to be "switchbox BC-348" written. There is a radio-command control box called a BC-348 -- but it looks nothing like the example here. That one looks more like something on a B-17. I was wondering if anyone had a good, clear photograph of this crystal-selector box so i can verify what the text reads.

The manual is wrong. The BC-345 [BC-348 is a complete liaison radio receiver used in many USAAF large aircraft. It requires a dedicated radio operator] is a range/voice switch that goes into the audio chain of attached radio receiver(s), and uses a separate FL-5 audio filter to either filter out all except a 1025 Hz tone, to reduce noise when receiving a radio range navigation signal, or filter out just the 1025 Hz tone so that you can hear voice signals more easily and with less distraction. The third position is "All", which effectively switches out the filters entirely. There are no crystals in it. See this link on my website for a clear photo and more on the early interphone systems: BC-213 and accessories

As far as I can tell, a similar radio setup was used in p-39D's, and P-40 series aircraft, as well as possibly the A-36\early mustangs, but without the crystal-select box. I also can't seem to find any sort of antenna relay control, so that is confusing as well.

The antenna relay is mounted near the transmitters and does not require any intervention by the pilot. It is automatically changed over to to transmit by the microphone or throttle switch.

Lastly, does anyone know what the DF loop on the back of some CBI p-47's was hooked into, and what sort of control box it had in the cockpit?

I could if you can reference a photograph somewhere.

[trys.bennett]

aafradio, many thanks!!

The whole system is starting to make much more sense to me now.

I don't have any of my own photos to post of the loop, but here are photos I've found on other forums that show the spine-mounted loop I was talking about...
Warbird Information Exchange • View topic - CBI P-47 Razorback for Scott D.
US Air Force - 10th Air Force P-47s
P47 Heaven :: LF Color photos of 1 ACG P-47s in CBI


The only possible clue I've been able to find, is that it might be part of a temporary Detrola unit intended for ferrying, and that it was intended to be removed

It would be something along the lines of this: http://www.radiomuseum.org/forumdata...Detr_front.jpg
or pictured in one of the manuals on page 11 at P-47 Manual (not a razorback, but I've seen it in that earlier manual as well).

That said, I've seen quite a few CBI-theater photos over the years that seem to show this loop in place, and not all of them looked like they had just come from states-side.

Any thoughts?

Many thanks!
Trys

[tourist]

The loop antenna is for the MN-26 Radio Compass.

[aafradio]

The receiver attached to the loop could be either a Bendix RA-10-** or MN-26-*. It's impossible to tell which from simply the antenna, but if I had to guess it would probably be a MN-26-* - the USAAF tended to go more for that model than the RA-10, which the Navy preferred. Either one used a manually steered loop. I have a short blurb on both at Navigation sets, Bendix RA-10, MN-26, RCA DZ-2, CRV-21562 Dynamotor that has the control heads, as well as one of the two optional loop antennas. I need to add the loop azimuth control head photo to the page - just haven't had time to update it. That control looks similar to the large indicator at the upper right on the control head page, but has a spinner knob added to manually rotate the antenna. Either receiver took the place of the Detrola in areas where the radio range was installed.