DX-40 is Alive!

[Richard H. Arland]

Gang:

I bought this clunker about 2 years ago from a guy who said "it looks
complete but I haven't fired it up". Translation: SUCKER!!!

After spending $75 on this puppy it became a personal quest to get it up
and running per factory specs.

Pulling the case revealed that at least 4 or 5 people had been inside
adding "modifications" to this classic rig. The wiring was a mess.
Someone in the distant past had added a T/R switch on the front and a
relay and SO-239 connector to provide T/R switching from the front
panel. As I powered the DX-40 up via the variac, the relay started
chattering. Clip...Clip....the relay was gone! This clipping continued
over several days.

In essence, the entire radio was gutted, right down to the chassis, all
the tube socket and terminal strip pins were cleaned, the power
transformer ran up and checked for proper HV output (there was some
"black stuff" leaking out of the secondary so I thought this was a
prudent step prior to undertaking any real in depth restoration).

The rig was rewired completely with new wiring and coax. The mic plug
was redone with new audio cable, grounded only at one end to reduce
ground loops.

The tubes check good and finally we fired it up yesterday, only to start
blowing fuses immediately. In the mess of rewiring, the function/mode
switch was wired incorrectly placing a short directly across the primary
of the transformer. After this was redone the rig fired up nicely.

First problem: no grid drive control There was about 2 ma of grid
current but no peaking when turning the DRIVE control . In the PHONE
position, with no audio going into the mic jack, keying the TX would
cause a motor boating of the output!

Gadzooks! Forgot to hook up the grid drive cap!

After that was done, everything was perking along just fine. The 40-W
light bulb dummy load was at more than full brilliance when the final
was properly tuned. Peak output occurred at about 90mA of Ip. Good dip
and peak with the final controls.

No output on PHONE with mic disconnected...that was a good sign.

So, this baby is now on my ops bench awaiting the rebuilding of the
VF-1. I have an Astatic D-104 that will work (I hope) with the DX-40 on
AM phone.

In the mean time, I'm rock bound on 80 and 40 meters. I'll try to get on
this weekend and give it a whirl and make some Qs.

73 Rich K7SZ

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