On Feb 27, 8:53 pm, "genev" wrote:
I just got an ARC 5 receiver and wonder if anyone has any tips on modifying
it; I had one in the 1960's, but can't remember what I had to do to it. I
think I replaced the dynamoter plug with a modern one, but dont remember how
I put the tuning knob on the front.
Also, what voltages are needed?
Thanks in advance for any info.
Richard
K1TAV


Richard. If your ARC-5 is original my strong suggestion is to not
modify the radio itself, except to fit some kind of tuning knob to
where the tuning cable was originally attached. You don't mention what
frequencies yours tunes. The most valuable model covers the broadcast
band. In mint (unchopped) condition some of those have sold recently
for over $100! And value is rising. Other frequency, unmodified ARC-5
often command $50 or higher.

It is not necessary to modify the receiver itself. I had one at around
age 14 which operated with an outboard power supply etc. the ARC-5
being completely untouched. It was my first superhet radio.

Information is readily available from other enthusiasts and on the web
about connections. I could forward some info if you wish.

Many of the 'chop jobs' done when these receivers were commonly
available (And cheap, sometimes as little as four dollars etc.) were a
shame and substantially reduced their value without improving the
ability of the receiver to work just as well as it did when installed
in an aircraft.

As you mentioned there is a 3 pin dynamotor plug on the back. You can
either connect wires to that to power the radio or power it via the
socket at the back. I have found that certain sizes of those blue
shelled crimped 'wire splicers/joiners ' commonly used to join say car
wiring will slip nicely and fit over those pins without destroying
them (some types will; some won't so experiment a bit) I do hope
somebody has not soldered to yours. It ruins them!

The sockets and plugs on those radios are a beautiful job of metal
pins mounted in mica. Some people have chopped them out and installed
various other types such as an octal etc. Some people have been able
to find an ex dynamotor base, or have made, a suitable base plate on
to which they have a mounted a small power supply; not very hard to
do. The advice about running the radios at much lower than the
original 250 volts DC B+ that the dynamotor put out seems to be very
good indeed. because the metal cased capacitors inside the base now
60+ years old can deteriorate, sometimes leak and/or short circuit.
have a fuse in the power supply no matter how you power it. Once or
twice power supplies specifically for that purpose have been seen on
eBay.

The 12 volt tubes are wired in three pairs so as to work on the 24 to
28 volt DC aircraft supply, so that heater current requirement is 3 x
0.15 = 0.45 amps at 24 volts. The 28 volts also powered the dynamotor
on the back of each ARC-5 receiver. Radio Shack used to sell small 115
volt input transformers that put out 24 volts at more than sufficient
amperage However many enthusiasts have transformer lying around that
may be suitable for the heater circuit and to provide B+. If you do
'have' to modify the heater circuit to 12 volts it will require about
0.9 amps. AC for the heaters is fine.

Even if done neatly other modifications to the front of the radio to
add a) RF gain control b) CW BFO on/off switch and sometimes also a
phone jack, usually involved butchering the plug in unit that goes in
the front secured by four small screws. It usually wasn't possible to
fit the controls into the small box that comes out so it and the
screened area behind it was often chopped out.

Some are lucky to have a one, two, or three position slide in plug in
rack into which these radios were mounted in the aircraft. They are
not very common now so it is usually necessary to connect wires in
some manner to the connector socket on the back of the receiver
itself. Best, if possible, to use some sort of small plugs to avoid
damaging the socket.

Somebody mentioned the gauge of wire that will just neatly plug into
each socket; maybe it was #6 or #8 AWG, I'll try and measure which
size fits firmly and tidily. And advise here.

From memory to get the radio to work it is necessary to provide power.
An RF gain potentiometer (no AF volume control was provided) and
provide a switch to ground (IIRC) the BFO oscillator lead. Another
caution is check whether the output transformer, which fed aircraft
headphones directly or the aircraft intercom system, could be set, on
most models for either low (600 ohm?) or (6000 impedance?) required
soldering inside IIRC. Volume output may seem low if set to high
impedance.

As mentioned a lot of this is from memory; I have six of those radios
downstairs but haven't worked on them since the 1950s! Three of mine
have been 'got at' and three are almost pristine but are all the same
frequency coverage.

There are most likley many people around who will have better
information; but am rushing this reply in order to encourage and urge
you from unnecessarily 'butchering' yet another 'Command' receiver as
so many were in the past.

As advised it is completely possible and was quite common to have a
power supply and all controls neatly outboard and to not have to chop
up the ARC-5 radio at all. One advantage being that if one then
acquired another ARC-5 it was not necessary to also modify it! Just
plug into the same power supply etc. and head phones, attach the
antenna and away you go.

Another seemingly unnecessary mod. that has been seen is that which
replaces the output circuit to provide enough power to feed a
speaker. The out put tube is a 12A6 which could provide sufficient
audio output. But attempts to do so often burnt out the primary
winding of the original 'potted' output transformer in the plate
circuit of the 12A6 tube. That led to replacement, inboard and
outboard OP transformers and sometimes the displacement of of other
parts. In one case someone added another tube on the back of the set
in a most untidy fashion!

If I can provide additional info which I have somewhere please
contact me. Again I urge, do not make unnecessary alterations.
Terry.