[Milsurplus] ER65

[Mike Morrow]

Mike asked:

> My question is: What is magic about 65 Volts DC for its
> power source?  Please note that 65 VDC powers the whole
> radio including the 12-volt heaters of the two tubes
> through the large dropping resistor shown in the chassis
> view, not just the B+ voltage. I doubt that a 67.5-volt
> B Battery could handle this current load, especially for
> any substantial length of time.

All merchant marine radiotelegraph installations were required
by Safety of Life at Sea (SOLAS) regulations to have a main
transmitter and receiver capable of operating in the 405 to
535 kHz MF maritime band.  There also had to be a reserve or
emergency receiver capable of operating 405 to 535 kHz A1 and A2,
and an associated reserve or emergency transmitter, plus reserve
antenna.  While the main transmitter was typically crystal-
controlled on seven or eight standard frequencies, the emergency
transmitter typically used a variable master oscillator.

The reserve or emergency MF radiotelegraph station was required
to function (receive and transmit) from power that was independent
of ship's power and could be placed in service within one minute
of normal power loss.  It had to supply the emergency receiver and
transmitter for at least six hours, including one hour of automatic
autoalarm-signal keying.  The condition of the emergency power was
required to be verified and logged daily.

Naturally, lead-acid batteries of the appropriate size were the
usual emergency power source.  There wasn't much standardization
of these supplies.  For example, the very common Radiomarine
Corporation of America's Type 4U Radio Unit that was installed on
most Victory ships used separate 6 vdc and 90 vdc lead acid
batteries for the emergency supply.

Your ER65 is a classic post-WWII design for a simple tunable
regen MF emergency receiver, capable of A1 or A2 reception with
only two tubes.  There would also have been an associated MF
emergency transmitter.  Doubtless, this particular installation
used a 65 vdc bank of emergency lead acid batteries.

At one time, a receiver was required to be available that
covered the required MF band without use of vacuum tubes.
That was still required in WWII.  That function was filled
in most cases by a very simple *crystal* receiver!

> Was 65 Volts DC a standard power source on some ships or
> shore stations, or did it require an external power supply?

The 65 vdc is characteristic only of the specific radio unit
or console of which the ER65 was a part.  It is not a ship's
supply voltage, nor is a standard value of any type for this
service.

So, it's got nothing to do with dry batteries or some alternate
supply to avoid running the main power source.  Typically,
the emergency receivers got their power from ship's power
through an appropriate supply unit, but 

After I left the USN active duty 34 years ago, I considered
spending a few years as a merchant marine radio officer.  I
was one of the small percentage of Navy folks who loved going
to sea.  So I passed the second class radiotelegraph operator
license and the ship radar endorsement, which are the main
technical qualifications.  However, within just a few months
getting the telegraph license, I developed a permanent medical
condition that disqualified me for SOLAS duties.  Regardless,
I kept a MF receiver near bedside for nearly 20 years to listen
at night to 500 kHz.  It was the most interesting spot in the
whole radio spectrum.  It all shut down in 1999...I've missed
it more than any other segment of radio operation.  A number
of US flag merchant vessels were reactivated in 1990 to support
Desert Storm and there weren't enough radio officers to fill
the new billets.  Because I had maintained my telegraph
operator's license, I received a solicitation from a radio 
officer's union to join up in 1991.

Mike / KK5F