[Milsurplus] SCR-183 question

[Mike]

Jack Antonio wrote:

> I'm working toward an SCR-183 setup, the BC-230 transmitter is up and running,
> with 5 watts out.

Ouch!  Take care of those rare (due to the audiofools) VT-25 tubes. 
Soon they'll be like VT-4-C tubes!

> Now is the task of building an ersatz TM-172 junction box.

Why not just buy a TM-AH-172?

OK, OK...that's my little joke!  I suspect the junction boxes are
extremely rare, since the manual for this gear says that normally its
function would be provided by a junction box built by the aircraft
manufacturer.  One wonders why the USAAF would want an aircraft to be
customized at time of manufacture for the installation of such an
archaic radio set.

> The manual shows the junction box and its schematic, but no parts list.
> I need to find the value of resistor 143.

I also have never been able to locate that information.  I have looked
at the USN manual (has more complete info) for the RU-16/GF-11
equivalent box, but the USN RU/GF-series is *grossly* different
electrically from the SCR-183/283 and there is no precisely equivalent
resistor.  The SCR-183 design is far far more primitive in comparision
to the rather refined (but still obsolete by WWII) design of the RU/GF.

One has to wonder at the incomplete nature of the information in the
SCR-(*)-183 manuals.  Though the junction box and resistor 143 and relay
153 would have likely been provided by the aircraft maker, still
troubleshooting by a radio tech would likely require knowing the value
of resistor 143 (in the oscillator/modulator HV supply line) for
replacement purposes.

> Also in the BD-AO-83 dynamotor, what is the value of resistors 146 and
> 152? 

According to T.O. 08-10-158 for the SCR-AS-183 (and BD-AS-83):

146 = 5,000 ohms, 2%, 10 watts wire-wound,
152 = 1,500 ohms, 2%, 10 watts wire-wound.

Being wire-wound, they have likely changed little in value.

> Again, the manual I have does not have that information.

Check under MISCELLANEOUS ITEMS in the Table of Replacable Parts.

> Lastly, I am assuming there would be no differences between
> the BD-AS-83 and BD-AO-83 Would this be a valid assumption?

I believe that to be true.  More knowledgable people on the list may
correct me, but I think most of the many letter distinctions in the
SCR-(*)-183/283 were due to there being different
contractor/manufacturers of basically the same gear.

What gets really confusing is all the tuning units whose nomenclature
varied with the various models.  For example, the tuning unit for 201 to
398 kc and 2.5 to 4.7 mc is the C-439 for the SCR-AS-183, but C-379 for
the SCR-AR-183.  That almost leads one to think that the coil from one
set was not intended to be interchanged with the same range coil from
the other set.

It is really amazing that the USAAF and USN continued buying this type
gear until at least 1943.  The SCR-183 is particularly nasty, though
today its antiquity of design is appealing.  Of course, you can hardly
ever find the transmitters with the VT-25 tubes in them anymore.

BTW, I'd love to buy receiver coil sets C-436 through C-440, a
MC-125/372/390 dial, as well as a TM-AH-172 for my SCR-AS-183.  Also,
I'm looking for SCR-274-N shock mounts FT-221 and FT-225 for the
3-receiver rack and modulator.  I know...fat chance!

73,
Mike / KK5F