[ARC5] Getting an "ARC-5 " Transmitter Running- Preparing The Transmitter

[Mike Morrow]

David Stinson wrote:

>2.  Unsolder one lead from the antenna relay. Roll
>the spring contact from the loading coil around so
> it's always in contact.

>3. Check the selector relay and make sure that the
>osc. B+ contact (the "short" one, nearest the coil)
>makes before the 1625 cathode contact. Carefully
>bend them to make sure. You key the rig with this
>relay through it's contact on the back plug-it's
>called the "selector."

>On "chirp-" This is a classic MOPA rig. While you can
>expect some small amount of chirp, I've got many
>transmitters in which it is difficult to hear any at all.

Hi David,

It makes one wonder why, when these rigs were in their ham heyday, so much ham "re-design" was thought to be necessary.  The basic design seems to be very sound for the era.  But it would be interesting to see measurements of the spurious output spectrum when the set is operated all original and under design conditions.

With respect to items 2 and 3 above, I wonder if putting the transmitter in as close to it's intended environment would work well, that is:

(1) Maintain pin 3 (for ARC-5) [pin 5 (for ATA or SCR-274)] grounded to energize the two select relays mentioned above (K-53, K54).  This simulates a remote control box select switch having selected this transmitter.  Relay contact closure timing then becomes a non-issue for these relays.

(2) Key the transmitter by using a Morse key to energize an external B+ switching relay.  This would perform the same function as the modulator unit's B+ keying relay K-52.  These sets were keyed by K-52 switching on and off the MO plate, PA screen, and PA plate voltages at pins 2, 6, 7 (for ARC-5) [pins 3, 4, 7 (for ATA or SCR-274)].

These two actions would employ the transmitter in almost exactly the same manner as the original system design did.  I've never tried it, though.  The last command transmitter I put on the air was 35 years ago, back in the hack-em-up days.

73,
Mike / KK5F