Edelpro Museum
for
Preservation of Vacuum Tubes and Analog Electronics
Part II – Radio Sets and Equipment
This section includes every kind of stuff worth of interest, of course
in the opinion of the author. It is usually believed that a collection must show
rare pieces by famous designers. On the contrary I just tried to prevent some
sets and pieces of equipment to be hastily scrapped. Many of them are usually
defined in derogatory terms as ‘boatanchors’, heavy piles of scrap metal.
Actually they were fine examples of the state of the art in their time and
their performances remained unsurpassed for years.
The most prolific period for electronics starts just before WWII,
reaches its peak during the war and goes on to the early sixties, when it
starts a fast decline. The huge growth of electronic devices during WWII is
evident when considering that just before the war the total value of electronic
equipment in a military or in an airline aircraft was less than 4000 US
dollars. Here the conveyor system
of the most advanced Chinese electronic factory during WWII. Few years later,
in the mid fifties, a single strategic bomber could carry over than 750,000 USD
of electronics.
At the beginning, new systems were hastily devised and designed, in
response to the pressing requests of the military. Over the years, systems were
perfected for the highest performances and reliability. But they retained two
primary characteristics, the full control by the operator and the full access
to every subassembly and components by technicians. Even in their simplicity,
those vacuum tube based systems were capable of performing satisfactorily the
tasks for which they had been designed. After all the space era, with its early
satellites, started with computers like the ones below.
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A mechanic computing machine,
the Monroe LN-160 about 1940 and the ad for the MOBIDIC, a military mobile
computer from Electronics, December 1957. (Click to enlarge)
German vacuum tube radios
I started collecting German radio sets for
their accurate design, resulting in reliable operation and in a remarkable
sound reproduction. The quality of these sets can be better appreciated when
compared with similar sets built in Italy in the same days. Most of the Italian
productions had no power transformer, the chassis being connected to the mains,
no built-in antenna, no tone controls, no multiple speaker system. On the
contrary, German radios were fine examples of engineering with a lot of
interesting solution, including:
Ø
Low-profile chassis, with
expanded tuning dials.
Ø
Power transformer and
insulated chassis. High-efficiency Graetz bridge selenium rectifier.
Ø
Internal AM/FM antennas, with
AM rotary loopstick.
Ø
Keyboard band/function
switching.
Ø
Smooth tuning systems with
reduction gears and flywheels. Dual coaxial knobs for AM and FM or a single
knob mechanically driven by band switching keys. Preset channels, band spread
dials and even motor-driven auto tuning.
Ø
Loudness control plus tone
controls and even tone registers. Sometimes IF variable bandwidth, driven by
the same tone control knobs.
Ø
Multiple speaker systems
including electrostatic or horn tweeters.
When I started the collection, AM broadcast
stations were already in progress of being dismantled. I focused then on FM
radio sets, which could still be enjoyed today. The drawback for most of German
sets is the poor FM coverage, limited to 100 MHz. Exhibits include radio sets
from the very early introduction of FM, around 1950, to the late FM-Stereo
vacuum tube radios, dated around the mid sixties. It is very interesting to
compare through the years the evolution of the audio section, amplifier and
speaker system, according to the evolution of sound sources.
Actually the very early sets were just AM
receivers with added FM tuner. Program sources a the time were the old
standard-groove shellac records. The design of audio amplifiers and speakers
was still centered on about 5 kHz bandwidth. With the introduction of
microgroove vinyl records, the bandwidth quickly jumped to about 15 kHz.
Speaker systems started to include tweeters. Early low efficiency electrostatic
types were soon replaced by dynamic cones and even by horn drivers.
The early approach to the stereophony, around
1957, was the 3D surrounding sound, with extra speakers added on both sides,
all driven by the same monophonic source. Later audio section evolved with
provision for full dual-channel amplifier. Even
if tuner was still mono, stereo sound was possible when listening from the
record player or from the tape recorder.
We have to wait until the mid sixties to see
full stereophonic sets. First the service was just experimental in very few big
cities and we find a simple socket for an optional stereo decoder. Soon later
the decoder was factory installed. Most of these new sets, known as
‘steuergërat’, came with external speakers, according to the standards
introduced by American Hi-Fi sets. But the Japanese industry was already moving
to full solid-state. After few hybrid solutions, German vacuum tube radios
disappeared from the scene.
The collection well shows the evolution through
some fifteen years, from about 1950 to about 1965, with a wide overview of
models mainly from Graetz and Saba, but also from AEG, Blaupunkt, Braun,
Grundig, Telefunken and others even from other countries. The exhibits are
divided into four major groups:
Graetz German
radios, about 1950 to 1965.
Saba
German radios, about 1952 to 1962.
Italian
and other brands
=================
Sound recording and reproducing sets
Another section covers some top
audio components and sets from the late sixties to the very early seventies,
years when I experienced several solutions to assemble a top sound reproduction
system: homebrew, French, German, Japanese, Swedish, Swiss and U.S. components.
My reference was a small Hi-Fi shop in Naples, Elettronica Meridionale, run by
a true audiophile, Mr. Raffaele Trombone. Thanks to a switch matrix, I could
compare the preferred kind of music sources reproduced by any combination of
record players, pick-up heads, amplifiers and speaker enclosures. Here I could
evaluate brands as AGA, Altec, Ampex, Acoustic Research, ERA, Fisher, Harman
Kardon, JBL, Klipsch, Koss, Marantz, Quad, Pickering, Revox, Shure, Thorens,
Uher and many more. Mr. Trombone was able to combine components of several
manufacturers to offer the best sound system for every pocket. I remember that
my first system was a combination of a Dual record changer, a Shure pick-up, a
couple of AGA bookshelf speaker enclosures and an Uher tape recorder also used
as power amplifier with its internal monitor amplifier. Mr. Trombone offered a
very attractive swap service. I tried several systems, up to the latest one
that I still preserve, as one of the finest ever done: two Empire Troubador
record players, one with an ADC XLM stereo cartridge and the other with a
quadraphonic Empire 4000 pick-up, a Marantz 3300 control console driving a
Marantz 500 power amplifier, a Nagamichi 700 cassette deck and two Klipsch
==========
Vinyl records
His section includes LP records from the
sixties and the early seventies. Female performers are present with over 50
titles by Connie Francis and a complete overview of Patsy Clyne. Other
categories include most of the volumes by Fausto Papetti and his sax, by Ronnie
Aldrich and his two pianos and several 4-Phase Decca records.
Still waiting for a complete inventory.
Communication receivers and related equipment
Communication receivers were the natural
evolution of the crystal radio, to listen to worldwide stations. Since I was a
children, I was attracted from the idea of listening someone speaking thousands
of miles away. I started with old surplus sets, an Allocchio Bacchini OC8 and a
military BC-
SW receivers range from a pre-war Hammarlund
SP-110, to some military BC-312s and to the well known SP-600, from a Collins
51J2 to the marvelous R-390A, to the late R-1051/URR, using only two vacuum
tubes, to some solid state receivers from the Italian Elmer line.
Communication gears also include some transmitters,
as the BC-191, and some transceivers, as the Wireless Set 19 MKIII and the
ARC51, equipping even the F-14 Tomcat.
============
Instrumentation
This section includes several beautiful
instruments salvaged from destruction, just because too quickly become
obsolete. It is divided in 5 major families.
Signal Generators and Frequency Meters
In my early years of electronics experiences I
only relied upon very poor test equipment, as those by Scuola Radio Elettra. My
dream was an accurate and stable frequency source, to check the calibration of
the several receivers I handled at that time. My very early stable frequency
source was a homebrew frequency standard, with 1 MHz crystal controlled
oscillator and two cascaded divide-by-ten multivibrators. I built it in 1965
and I still preserve its chassis, or what survived the children of a guard that
took care of my country house. Nice job for a guy of just nineteen! The first
accurate generator I found around the mid sixties was a BC-221Q frequency
meter, for which I built a stabilized AC power supply. Unfortunately it was
unmodulated and its maximum frequency was limited to 20 MHz. In the sixties and
up to the early seventies few signal generators were affordable in military
surplus. Nevertheless I had found some military generators, and a couple of
huge HP 124B counters, capable of operating up to 100 MHz with their heterodyne
plug-in prescalers. Then I decided to give away them all.
In recent years I found several old frequency
generators and counters coming from the dismantling of old service shops and
laboratories. The collection includes a wide spread of equipment ranging from
military WWII test sets to standard generators, to microwave generators, to
radar test equipment, up to frequency meters and counters. Most of the sets are
complete with their technical manuals. Smart operating principles and
remarkable solutions used to enhance performances of most advanced sets are
often focused in the description of each device.
Also available in this section are some
frequency meters, including digital counters. Among these, we can see a trochotron
frequency meter by Van Norman Industries, fully operating and believed to
be one the finest examples of electronic archeology.
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Oscilloscopes
This section is almost entirely devoted to
Tektronix, the worldwide leader for this kind of instrumentation since the fifties
and well in the sixties. In those years almost every electronic firm sold its
own line of test equipment and of oscilloscopes but in their advanced
laboratories all of them used one or more Tek scopes as reference. A Tektronix
could cost more than a small flat or a Ferrari car. For this reason I accepted
the idea that I could just use these instruments at the University, since I
would never buy one. Tek scopes were very expensive, but they were worth money
paid for. Traces were sharp and bright, vertical amplifiers and time bases were
accurate enough to make possible a reliable evaluation of observed waveforms
and added features as the dual time-base, the intensifier or the magnifier
helped to catch every details. But the most outstanding features of these
instruments came from the accurate design of trigger circuits, able to lock on
any point of the input waveform at any frequency and with vertical deflections
of just few millimeters. Even the internal look was unique, with the shining
rows of passive components and of neon bulbs aligned between couples of ceramic
notched strips and with the tiny roll of silver-loaded soldering alloy, added
somewhere inside for in-field emergency servicing.
Few oscilloscopes of other sources are added to
the Tek ones. The most relevant samples, for their Tek-like complexity, were
built by a small and smart US manufacturer now almost forgotten, Lavoie Labs
from Morganville, CT, founded by Steve Lavoie. Remarkable are the mainframe
LA-265A, equivalent to the Tektronix 545A, and the plug-in vertical amplifier
LA-265-CA, equivalent to the Tek CA plug-in. From Lavoie Labs also a huge
military set, second source of a HP rack oscilloscope built to military specs.
==========
Tube testers
In the sixties a tube tester was an expensive
oddity. Vacuum tubes were readily available and quite inexpensive, at least the
receiving ones. One could buy hundreds and hundreds of new tubes for the same
money asked for a simple emission tester. Heaters were readily checked with an
ohmeter. And at its best the tube tester could just give a low-emission reading
for a tube but did not help to return a radio or a television set to its normal
operation. On the contrary, simply replacing the old tube with a new one,
resulted not only in a more reliable indication but even solved the faulty
operation. Radio and television repair shops preferred to have caddies or
shelves with assorted spare tubes. Those wealthy people who had bought a tube
tester used it to screen all the discarded tubes for some improbable future
uses.
Tube testers gained popularity when the
production of vacuum tubes ceased. Old tubes, often pulled from equipment
withdrawn from service, could be returned to a new useful life, after checking
their emission on a tester.
I don’t like tube testers: they are just useful
to match tube pairs. The most accurate models are even the most cumbersome to
use, with the need of setting bias and load conditions for each tube, in
addition to the pin configuration and to the heater voltage. My preferred types
are the U.S. military I-177 or its updated version TV-7, simple to use, fast
and reliable.
The collection includes the above types, the
AVO MK4 characteristics meter and some Italian models.
============
Multimeters, VTVMs, DC Standards
This section includes several kind of analog or
digital voltmeters and multimeters, intended for measurements of voltage,
current or resistance values. These measurements were performed in the past
using analog meters, based upon some D’Arsonval type microammeters with the
addition of voltage dividers and of current shunts. The full scale sensitivity
of best meters was in the order of 50 microamps, resulting in an internal
resistance of 20 kohms per volt when used as voltmeters. Hence, if a full scale
value of 10 volts was selected to measure the control grid voltage of a vacuum
tube, the voltmeter internal resistance was in the order of 200 kohms: this
value is found in parallel with the grid resistor and can considerably alter
the operating point of the tube. To measure these small voltages vacuum tube
voltmeters, VTVMs, were used. Here a vacuum tube amplifier, usually connected
in a balanced bridge circuit, grants very high input impedance. Common values
were 10 mohms for DC voltages and 1 mohm with few picofarads for AC values.
The collection includes some of the most
appreciated multimeters, including two versions of the insuperable AVOmeters.
These were very accurate, with the moving coil on friction-free taut-band
suspensions, yet almost indestructible, with their patented overload cutout.
Until the late sixties AVOmeters, as well as other high-class multimeters, were
supplied with high-voltage ranges, 2500 volts AC or DC in this case. Later, due
to some stupid safety rules, maximum handling capability was limited to 700 or
1000 volts.
Vacuum tube voltmeters include the well known
HP 410B and the RCA Senior Voltohmist, both fully restored.
Also available are some different kind of
electronic voltmeters, as true RMS digital voltmeters, differential voltmeters,
precision digital voltmeters and insulation meters.
This section is completed by some voltage
standards, based upon Weston cells.
Weston cells have been in use since 1905 as primary standards.
=============
AC measurements
This sub-section shows several instruments used
to measure AC or RF magnitudes. Here we find AC bridges, vectorial voltmeters,
but even some early X-band radar test sets from WWII.
