Edelpro Museum


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.



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.


More German brands


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 La Scala folded horn speaker enclosures. A Koss electrostatic headphone, a Philips CD player and a Revox reel-to-reel tape recorder completed the system. Few items were changed in the years. The Marantz 500, waiting for service, was replaced by a homebrew vacuum tube amplifier, while the Nagamichi and the Philips decks were replaced by Revox units.







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-348. In the late sixties I owned several communication gears, including some German Feldfunk and Funk sets, an Italian RF4 set (the one in the movie ‘I due colonnelli’), a Collins R-392 and a complete RTTY receiving station, with Allocchio Bacchini OC11 receiver and  the FSK decoder, a Teletype mod 15 fully restored, a TXC-1 military facsimile equipment, some 10-inch reels tape recorders, a Revox C-36, a G-36 and an Ampex with tuning fork controlled AC power source. In the early seventies I threw away everything, several racks of equipment. More than twenty years later I started again to collect the few items I could find. Today the collection includes several short-wave communication receivers,  few transmitting gears and some transceivers.


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.






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.







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.