[ARC5] Update on the Heath HT-4 aircraft transmitter

[Robert Nickels]

It's been a week since Dave AB5S kick-started my interest in getting 
this little transmitter on the air, so I thought an update might be of 
interest.

Like Daves, my "high power" version basically worked right off, although 
one RF choke has been replaced at some point.   The only issue I had was 
with the T/R relay, which refused to do anything but buzz with AC, and 
which is wired into the complex 6/12 volt selector switch, making it 
difficult to power separately.  But an easy fix was simply to use on old 
5 volt regulated power supply cranked up to max, along with an as-found 
hamfest special B+ supply.

I lashed the whole works up on a piece of plywood and cabled up a little 
Pierson KE-93 mobile receiver to see what I could do on the air.   With 
300 volts to the 6V6, I was seeing a solid 6 watts on a Bird, and good 
modulation - in fact it's pretty easy to overmodulate with the carbon 
mic shown.

Todays test on the Midwest Classic Radio Net produced S9 signal reports 
from stations 200 miles away using a ladder-line fed dipole at 60 ft!  
I'm very pleased with how the HT-4 works and would encourage others to 
take a look at some of the old mobile rigs if you're intrigued with what 
can be done with QRP AM.    By the way, I've repackaged some of the 
cheap crystals from N4ESS into old FT-243 holders, so I'm good to go on 
both 3880 and 3885 (the little crystals work fine in this oscillator 
circuit).  Or, if you can't find an old aircraft radio to play with, 
don't overlook the marine band AM radios that turn up often and are 
easily converted to ham band use.

73, Bob W9RAN