[ARC5] ARC-5 VHF sets

[Mike]

John J Mccarty wrote:

> Pick up a T-23 recently. ...  I assumed that an "upgrade" from ARC-5
> H.F.to V.H.F. would just require installing the radios in the rack,
> changing the contol boxes, and running a new cable from the C-30 control
> box to the front of the transmitter to select channels.

Close, but...

>  But I started to look at the pin outs, and maybe it's not quite that
>  straight forward. The T-23 uses pin 1 along with pin 7 to bring in H.V.
>  Is this just an added jumper at the rack ?

No, for the VHF T-23/ARC-5:

Pin 1 (unused on the HF/MF transmitters) should be connected 
      directly to full UNMODULATED HV for the plates of the three
      tubes that are BEFORE the final 832.
Pin 2 should get a reduced UNMODULATED screen supply voltage for the
      three tubes that are BEFORE the final 832.
Pin 6 should get reduced MODULATED screen voltage for the final 832.
Pin 7 should get full MODULATED plate voltage supply voltage for the
      final 832.

Additionally, the REAL purpose of running a line through pin 1 to full
unmodulated HV is that a relay K-306 in the T-23/ARC-5 in effect
connects a 15,000 ohm 15 watt resistor R-329 across the MD-7/ARC-5
modulation transformer plate winding output to load down some of the
modulator audio output that is excess to the needs of the low powered
832 final in the T-23/ARC-5.  Since the MF/HF transmitters need all the
modulator's output, it was not necessary to run the HV to pin 1 for the
connection of an audio load resistor in the MF/HF transmitters, so pin 1
is unused on them.

If you are going to use a low output modulator just made for the low
power 832 final, you may want to disconnect one end of R-329 in the
T-23/ARC-5 so that you don't waste some of the modulator's audio output.

> Control box C-30 only selects xmitters 2 and 3 ? 

The C-30/ARC-5 is wired to always select transmitter number 1 whenever
ANY VHF channel-select button A though D is depressed.  The transmitter
rack has a selector plate near each transmitter connecting plug. 
Normally the transmitter on the left would be number 1, as designated on
the rack's selector plate at that position having its center terminal
connected to terminal 1.

On the C-30/ARC-5, depressing button 2 or 3 deselects the VHF
transmitter in rack position 1 and selects the MF/HF transmitter in rack
position 2 (rack selector plate connected to center terminal to 2) or
the MF/HF transmitter in rack position 3 (rack selector plate connected
to center terminal to 3), if one exists.  Thus the C-30/ARC-5 can
control one VHF and up to two MF/HF transmitters in up to a
three-transmitter rack.

The C-30 also selected the same channel number on the R-28/ARC-5 VHF
receiver, though the other receiver functions were controlled by control
units like the C-38, C-42, or C-43/ARC-5. 

The C-30/ARC-5 was later replaced by the C-30A/ARC-5, which controls up
to four transmitters, and allows the VHF transmitter to be in rack
positions other than number 1.  It's smaller too.

> Does the other connector on C-30 select the channels on both the TX
> and RX via a split cable ?

The same 18-conductor cable assembly that would have gone from the
MD-7/ARC-5 to the C-29/ARC-5 MF/HF transmitter control box would go
instead to the 18-pin connector on the C-30/ARC-5 VHF and MF/HF
transmitter control box.  The 12-pin cable from the C-30/ARC-5 would
split to a 6-pin connector going to the front of the R-28/ARC-5 VHF
receiver, and a 8-pin connector going to the front of the T-23/ARC-5 VHF
transmitter.  This would be either wired in a harness in that
configuration, or split through a special junction box J-28/ARC-5.

> I guess I'm asking if the H.F. and V.H.F radios set up in the same racks,
> on were they never mixed ? The RX control box looks to me that mixing was
> the idea.

Yes, though obsolete by the time it appeared, the AN/ARC-5 and AN/ARR-2
systems were bewilderingly varied and versatile in arrangment.  In
general, it was designed to have MF/HF AND VHF units in the same rack. 
My pet arrangement is:

Four receivers in a four-receiver MT-67/ARC-5 rack, as follows.
   Controlled by C-38/ARC-5:  R-28/ARC-5  VHF (channel selected by
C-30/ARC-5)
                              R-26/ARC-5  HF (locked frequency)
                              R-4/ARR-2   Special homing receiver
   Controlled by C-26/ARC-5:  R-23/ARC-5  LF/MF Range Receiver (remote
variable tuned)

Two transmitters in a two-transmittter MT-71/ARC-5 rack, as follows.
   Controlled by C-30/ARC-5:  T-23/ARC-5  VHF
                              T-20/ARC-5  HF

Plus one needs the supporting RE-2/ARC-5, MD-7/ARC-5, DY-8/ARC-5 and
DY-2A/ARR-2 units, etc.  (I'm still trying to accumulate all the items I
need for this system.)

Thus one "system" could provide range receiver, homing receiver, plus HF
and VHF communications receivers and transmitters.

73,
Mike / KK5F