AT-1 Transmitter by Heathkit
My Heathkit AT-1 project
The Heathkit AT-1 Transmitter Kit... The lowest possible dollar-per-watt price in the early
50's. "Panel mounted crystal socket, stand-by switch, key click filer, A.C. line filtering,
good shielding, etc. VFO or crystal excitation--up to 35 watts input. Built-in power
supply provides 425 volts at 100 MA. Amazingly low kit price includes all circuit
components, tubes, cabinet, punched chassis, and detailed construction manual."
SPECIFICATIONS: Range... 80, 40, 20, 15, 11, 10 meters. Oscillator-multiplier...
6AG7. Amplifier-doubler... 6L6. Rectifier... 5U4G. Power requirements... 105-125
Volt A.C. 50-60 cycles 100 watts. Size... 8-1/8 inch high x 13-1/8 inch wide x 7 inch
deep.
MISC: 80 meter crystals must be used on 80 and 40. Drive control has no affect on 80,
because it's switched out of the circuit. Use 40 meter crystals on 20. Power output is
about 10 watts.
The AT-1 I found wasn't anywhere near the shape of the one in the above picture. The case
was bent, and from the looks of it, the radio was probably dropped on one of its back
corners. The front panel had scrapes and dents, and an extra hole was drilled for a pilot
lamp. The plate-standby switch was also not original. Certainly, 50 years of abuse was
evident. I suppose I could have cut a new aluminum panel, and paid $60 plus to have it
repainted and silk-screened, but I decided to work with what I had.
Sanding and painting the old panel wasn't a big job, but the decals presented a problem.
You'll notice in the picture to the right, the lack of 0-10 gradients around the tuning
controls. The reason for omitting these is the difficulty working with such large
decals. You'll see on the finished product that the circles around the band selector have
also been omitted for the same reason. However, if you have the patience, they are included
on the decal templates available for download below, but you're on your own.
Pictures of the chassis before and after restoration are shown below.
BEFORE
AFTER
BEFORE
The chassis was completely stripped, cleaned and re-wired. The standard re-cap routine was performed, resistor values were checked and all controls were cleaned. Fuses and holders were added...one to the transformer primary and one to the high voltage secondary. Since holes were drilled, and non-original switches were used, I went ahead, replaced one, and added another. The cabinet and front panel were repainted, and decals added as mentioned before.
AFTER
The Finished Product
The following decal templates are presented as a guide only. It's best to make the graphics
twice the normal size and send the image to the decal paper at 50%. Print to regular paper
first and make final adjustments to the size.
I used Testors inkjet clear decal paper. After waiting for the printed image to dry for a
couple hours, I coated the paper with Testors Decal Bonder #9200, and let it dry for 12 hours.
DOWNLOADS:
Decal template 1
Decal template 2
Decal template 3
The AT-1 schematic diagram. Diagram of
function switch.
Note: Signal Electric (Menominee, Michigan) Navy Type key displayed on top of transmitter.
Heathkit Reflected Power and SWR Bridge
SPECIFICATIONS: Operation... Indicates percentage of forward and reflected power, and
voltage standing wave ratio (SWR). RF Power Handling Capabilities... One
kilowatt. Input And Output Impedance... 50 or 75 ohm. Band Coverage... 160
through 6 meters. Dimensions... 7-3/4" wide x 4-5/8" high x 4-1/16 deep.
MISC: The circuit of the Reflected Power Meter and SWR Bridge is based upon that of a device
developed at the U.S. Naval Research Laboratory. As much as 75 watts may be needed on 80
meters for full scale deflection, and as little as 2 watts on 6 meters.
Is it a rare Heathkit find or a long lost and forgotten prototype? No, but it is one of a
kind, and another example of working with what's given you.
This meter started off in life as an HM-11, but when I got it, it hardly resembled any known piece
of hardware, so I improvised. The meter was cracked and the knobs were missing, but the
price was right...free!
I painted the dented and scratched case to match the AT-1, replaced the meter with a NOS one from
'61, and finished it off with a couple AT-1 style knobs. I also changed the two 1N34A diodes
to a matched set, and calibrated the bridge.
A purest may not like reincarnating old gear, but in my opinion, it's better than throwing it in
the trash.
The AM-2/HM-11 schematic diagram.
The Whatever Wattmeter
