400Hz power for 618T-3 From
a Car Power Inverter
JA6ATY, Takashi Inouye
To get a 618T-3 radio up and running, one major problem to conquer is the 400Hz AC power.
This kind of power isn't normally found in a ham shacks .
The most conventional way is to procure this power is surplus equipment such as 426T-1,488A-2 Etc
However, these devices are becoming hard to find , and moreover many surplus stores, especially in the USA
'can not' or 'will not' export.
an alternate to surplus 400Hz supplies
I started looking into alternative power sources I thought why not try to convert
a Power Inverter intended for use in auto's. Here in Japan, these Inverter are DC12V
to AC100V , which is the normal power line voltage in Japan.
These inverters are available almost everywhere, and on the internet, plenty of low cost units,
you don't need 10Kw unit, when a few hundred watts will do the trick for the 618T.
My idea was to modify this inverter to produce the 400 Hz for 618T-3. If only the manufacture
of these devices would supplied a schematic diagram, Great Idea, but it's only a dream.
so What to do, The trial and error method
we need to find which components control the frequency
In my case, I got the following inverter.
type HG-350/12V by Cellstar link1 link 2 english link
output 100VAC (55Hz)
I jumped right into the trial and error process, BE careful DONT just start shorting out components hoping
for results, the result might be smoke, I got very lucky, when I opened the case , I found there were only
three pot's (potentiometer) on the printed circuit board. I was very happy, thinking one of these must adjust the Frequency.
I Connecting a frequency counter at the output and adjusted each pot a small amount,
once I found the one that effected the frequency , I inspected the other components on the board, I determined
the pot was labeled VR2 was 30K variable, it was connected in series with R33 (47K) fixed resistance. I tried another
47K in parallel. That cuts the resistance in half, and the frequency took a big jump, after trying a lower and lower
resistance, I found I could just SHORT out R33 and by adjusting VR2 could get it right on 400Hz. How great can this be ??
I can only hope your luck will be as good as mine if you use a different brand inverter.
I am now using one of these on my 618T, everything is working fine
the output of the inverter is "sort" of a square wave, basically the same output as the Collins 426T-1 which also outputs a square wave.
in fact, per Collins : 115V 400Hz. 630Va . you folks in Europe be careful , your car inverters probably put out 220V
it might be better to get on like mine or get something from the USA since they have 115Vac..
best wishes Takashi pdb00507((at))nifty.com
Heres a few pictures..