[R-390] My First Boat Anchor...

[Bill Hawkins]

Congratulations on becoming the owner of the finest in vacuum tube
receiver technology. You may want to look at others in the series.

Let me be the first to kick over the grounding can, so to speak.

The grounded three prong line connector was invented in 1927, but it
didn't catch on right away. Europe made it required by law in 1965.
Three prong outlets were not common in 1955, hence the 390 has a
two prong plug.

The sets were expected to be installed in grounded enclosures, common
since the beginning of commercial electricity. This took care of RF
grounding as well as safety grounding.

The original line filters have 0.1 mfd capacitors from line to ground.
The reactance at 60 Hz is about 10,000 Ohms. This is enough to lift
the case to a tingling 60 volts above ground if you fail to ground the
case properly.

The sets were not designed for outlets with ground fault interrupters.
If you plug a properly grounded set into a GFI outlet, it will trip.
The only way around this is to use an isolation transformer, so the
GFI doesn't see the reactance (not "leakage") current from the line
filter.

However, the set is not being used in a military environment, where
0.1 mfd caps were required. For home use, 0.01 mfd is adequate, if
you need a filter at all. This modifies the set from its original
design, which is not always acceptable. Same goes for the plug.

The other thing you can do is to eliminate the GFI outlet.

In any event, ground the set to a metal water pipe. #14 copper is
adequate. If you have transmitters, use that ground. Or, you can
connect the ground wire to the ground pin in an otherwise empty
plug. Plug that into a three prong receptacle that you know is
grounded.

Let the discussion begin . . .

Bill Hawkins


-----Original Message-----
From: Mark VandeWettering
Sent: Friday, April 06, 2012 7:22 PM

Howdy all.

I've just acquired my first true boat anchor: a Collins R-390A bearing
the Motorola serial number 519, and by the order number on the back,
appears to have been manfuctured in 1956.  I acquired from my boss as
he's retiring and downsizing.   It appears to be in very good
condition: front panel is immaculate.  The inside is a bit dusty and
grimy, but all the mechanicals seem good upon inspection.  A couple of
things worry me about the radio though: the power cord seems very
light weight, and is a two prong connector.  My primary concern above
everything is to make sure that it is safe to operate.   Beyond that,
I've got very little experience in cleaning and maintenance of this
kind of vintage equipment.

Can anyone recommend some resources?   Initially, I'm looking for a
"best practices" modifications to improve the electrical safety, but
beyond that, I'd like to to get some guidance on how to proceed to
clean and tune this radio.  Any links/information helpful to the
beginning boat anchor enthusiast would be helpful.   Anybody in the SF
Bay Area who might be willing to act as an Elmer would be even more
helpful.   I've never tackled a project quite like this before, and
I'd like to benefit from the experience of those who do it right.

Thanks gentlemen!

Mark K6HX