Cheyenne MT-1 High Jinx

Brian Carling bcarling at CFL.RR.COM
Sun Dec 21 11:35:21 EST 2003

High Jinks:
Playful, often noisy and rowdy activity, usually involving mischievous pranks.

Nope... this was mostly High JINX:
1 - A person or thing that is believed to bring bad luck.
2 - A condition or period of bad luck that appears to have been caused by a
specific person or thing.

The Saga of A Non-functional MT-1 Heath Transmitter

Winter has finally come to Central Florida.
Many of you that live up North (Yes, even GEORGIA is "up north" to us!) - you
folks do NOT understand that we DO have seasons down
here and it is right chilly outside, so it's the time to work on some
old toob gear again.

This Cheyenne looks pretty good, but she doesn't work!
It came with the matching AC supply and cable which encouraged
me to make the effort to get it on the air this winter.

The P.S. was tested and found to deliver 730V and 350V DC plus
about 12.8V  AC under load. All good so far.
I tested all the tubes - and they are all showing good emission.
Most are the original "Heathkit" labelled tubes which I
think is cool.

However, the T-R relay does not energize when you turn
the function switch to the "CW" position. If I ground the
PTT line she pulls in just fine. After some digging I found
that they wired the filament string series-parallel for
12.6V AC operation.

Good so far, but THEN I measured the voltage on
the 6146 side of the string and found just over 3 volts AC.
Uh oh! Problem there! No wonder the pilot lamps look dim
and nothing works!

My first thought was that the dial lamps may
be replacements of the wrong type. They look old.
Type 47 - three in parallel.

That makes a total of 2350 mA on the 6146 / 6CL6 and the
#47 lamps X 3 all in parallel on one leg.

The other leg in the series has the 12AX7 / 6AU6A / 5763 /
6DE7 tubes and that parallel group has 2250 mA accoring
to my calculations based on good olde ARRL Handbook data.

So it's pretty close to being balanced! I wondered WHY I am having such a bad
balance problem. I would BET that there is a wire broken somewhere in this thing!

I started to try to check the filament voltage on the underside
of each tube socket. Most of them were impossible to get
to - especially the 6AU6A VFO because the whole assembly is
inside a nice isolated aluminum sub-box with no exposed parts
or wiring! Several of the other tubes had large parts in the way
that prevented the attachment of any meter probes.
I started to take the metal shields off one at a time to see
if any of the tubes were completely un-lit. As I went to
pull the cover off of the 6DE7, I moved it a little and the
pilot lights suddenly sprang to full brightness!

No more filament JINX ! !

Now I just need to figure out HOW the T-R switching is
supposed to work on CW. It works fine on phone from
the PTT switch at the mic input connector.

Does anyone else out there using a Cheyenne and have
any further tips?

73 & Happy Christmas / Hanukkah to all!

Bry, AF4K
Sanford, FL

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