[Collins] Re: collins 618T-3

[Dr. Gerald N. Johnson, electrical engineer]

110 volts 3 phase 400 Hz won't be convenient and the internal 618T power
supply won't appreciate any lower frequency. Its probably not especially
picky about higher frequencies. But it will have to be three phase. With
a bit of work, a variable speed motor controller might work, but it will
have to be putting out that voltage and frequency and some crude
approximation of three sine waves.

There are commercial supplies for just that purpose. They might be found
in industrial test equipment stores, but the price won't be very
reasonable.

The other alternative is to find a 3 phase alternator and run it at a
speed to produce 400 Hz. Leece-Neville heavy duty alternators already
bring out the 3 phase AC connections. One I have, I figured would need
to run on my tractor at something like 1000 engine RPM or faster with
the present pulleys to produce 400 Hz and thus to be stepped up to 120
volts with a 400 Hz transformer. There surely are aircraft three phase
alternators about too. They might need to turn a few thousand RPM
depending on their design.

There are rotary inverters that take in 28 volts and make 110 volts
three phase, but most of them won't run a 618T, they are made for
instruments and those that would run a 618T will draw 100 amps at 28
volts when running, probably 300 amps starting and I've not detected
their input current varies (at least not the little ones I've tried,
unless they've suffered from shorted windings) from no load to full
load.

A decade or more ago, a couple 618T showed up in Iowa Army MARS. KD6B
did succeed in getting manuals and in making one from several, but was
continually having to replace SUHL logic chips to keep them on the air.
He's moved from the area taking the radios and I don't know if he still
has any working or not.

Much was sacrificed in making the radios compact and lightweight. Power
supply, accessibility, repairability...

73, Jerry, K0CQ, Technical Advisor to the CRA

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.