Mid-Atlantic Antique Radio Club - MAARC

05/29/2026

Catchup time, and we have some good stuff to share.

On May 16th we had a post about early loose couplers used with crystal sets. Bryan Gadow commented "Some years back the pastor of the church we were attending went home for a vacation; when he returned he gifted me a more rustic version of the one pictured. (Some relative of his had it.) Through the windings I can still read the label of a Mother's Oats box! I have had it working, though it was very weak. I need to give it another try one of these days. It wasn't clear what all the connections were." Ed Lyon stated "I have had several of them over the years, traded most for other things that I needed. I still have several, one of which is built into the finest radio ever made, the SE1420 built for the Bureau of Steam Engineering (hence the “SE” in the model number)." Thank you for sharing Ed and Bryan.

Incidentally, there is quite a bit of information on the web about the Navy SE1420 radio, including a user manual dated March 1919. It was designed by Louis Hazeltine, built by the Amrad Corporation, and functioned to receive medium frequency and long wave transmissions in the range between 235 TO 7500 meters (or 1,276 kHz (broadcast band) down to 40 kHz).

On 21 May we had a post on the AVIDAC computer. Ed Lyon replied "Interesting story, especially its time in history and the people involved, at least for me. I had just gotten employed by ERCO, the flight simulator people, early in November 1953, and was in the early stages of success in getting the first long differential equation (solving for forward velocity vector of an aircraft having an array of drag surfaces exposed , a variable-thrust jet engine, a resultant dead-mass plus variations due to fuel remaining, occupancy, munitions weight, etc.,) and both static and motion-related inertial and gravity forces, etc., when our company got a request from Argonne National Lab forwarded to us. It asked us what the parameters of an analog computer for problems solving for the cross-correlation function between low-frequency noisy parameter histories would look like, so we hand-wired a generic one, using the components of the F-86D longitudinal-axis motion computer string of Serial Number 31 of the total 66 simulators that were ordered for that aircraft, during the Christmas-New Year week. The Argonne people thanked us for the quick test, and said they were going to configure one as a real-time check on that phase of testing of their “big” computer and of the swimming-pool reactor controller they had under trial at the time. I guess the “big” computer they mentioned was this early digital computer you described." That just may be the case Ed. Glad that post was able to fill in the blanks.

On 22 May we had a post about Klipschorn speakers, which prompted David Poe to write: "I had a pair of Klipschorns from about 1992 until about 2015. They were not the most musically accurate speakers, but they could reproduce music at live levels effortlessly. That's the most descriptive statement I could make about their character - effortless. I drove them with several different amplifiers, ranging from a Dynaco Stereo 70, a Dynaco SCA-80Q, a Carver M400t, and a few other amps. I first heard them at a stereo shop ("HiFi House") when I was in college in the 1970's and was totally blown away. I got a brochure and carried it around for years. When I was dating my future wife back in the 1990's and showed her the brochure, she said "You've been carrying that brochure around for over 20 years - you should get a pair!". BEST (future) WIFE EVER!!! So I started looking in the classified ads in the Washington Post. It took nearly a year to find a pair for sale that hadn't already been sold by the time the Sunday newspaper hit the street. I bought them from a fairly young kid who also had a pair of La Scalas. I don't know what he did for living, but he lived in a big house in Annapolis and also drove a Porsche. By the mid-2010's, we just weren't listening to music that much anymore and decided to sell them. I put an ad on Craigs List and the responses started coming in within an hour. The woman that bought them lived in an apartment... I told her that her neighbors were going to HATE her. I sold them for more than I paid for them, but still miss them greatly." Thanks for sharing that Dave.

More catchup tomorrow.

05/28/2026

Today we are just 1 week away from MAARC's biggest event of the year, the Vintage Electronics Expo we refer to as RadioActivity. This 3-day event kicks off with a vacuum tube and ephemera auction on Thursday night June 4th. Friday kicks off with both indoor and outdoor vending, followed by a meeting of the Tube Collector's Association and other presentations focused on modern day tube testers, WWII aircraft radios, and Hi-Fi. Our evening banquet features speaker Jim Cross on vacuum tube tales and a viewing of our Old Equipment Contest. Saturday kicks off with a walk-round auction of this and thats plus a radio repair clinic, and wraps up with our main auction. For more details, click on this link: https://maarc.org/radioactivity-2026/

Today's post addresses the popular Zenith Trans-Oceanic radio. It was authored by MAARC co-founder Ted Hannah, and was originally published in the May 1993 "MAARC Newsletter." It is entitled "DISASSEMBLING AND REPAIRING A CLASSIC: THE ZENITH TRANS-OCEANIC."

"A fair amount of literature is available on repairing the Zenith Trans-Oceanic radios, but not much has been written on getting to the chassis so that you can make the repairs. While disassembling one of the later tube-type models, I made some notes that may be helpful to others who need to remove the chassis from the cabinet. The set I worked on was the Model Y600L, Chassis 6T41Z, from 1956, an unusually handsome and comparatively rare set covered in brown top-grain cowhide. (The "L" in Trans-Oceanic model numbers tells you that it is a leather-covered set.)

The disassembly procedure I followed is generally applicable to all the tube-type models, although some steps, like removing the phone jack and dial light, will not apply to the earlier sets. Here is how I did it:
o Remove both k***s.
o Remove the nut and washer from the phone jack on the front panel.
o Open the back cover and unplug the Wavemagnet antenna (the red ribbon that plugs into the chassis just behind the tuning capacitor).
o Remove the Wavemagnet antenna from the cabinet.
o Remove the wood screw from the bracket near the telescoping rod antenna. (The screw fastens into the underside of the cabinet top.)
o Unplug the connector to the telescoping rod antenna and remove the antenna by removing the two nuts and washers that hold it in place.
o Slip the dial light from the bracket near the front of the tuning capacitor.
o Remove the two screws that hold the chassis down to the wooden shelf. (They are accessible through holes in the bottom of the cabinet.)
o Carefully slide the chassis out of the cabinet, being sure that the ac plug at the right side clears the cabinet, also that the fine wires in the coil assembly at the left are not disturbed.
o While the chassis is out of the cabinet, notice the date stamped on the top of the wood shelf. This is the date your radio was manufactured.

To reassemble the radio, just reverse the steps above. If your radio is like the one I worked on, you may wish that the wires to the phone jack were just a few inches longer. And be sure that the wires to the dial light are toward the front of the cabinet, away from the RF coils.

Inside: A Common Problem

The reason I had to get into the chassis was that after the radio had been on for about 15 minutes, the signal would become garbled and begin to fade out, particularly at the lower end of the broadcast band and on all or most of the shortwave bands.

The source of the problem was a weak selenium rectifier, whose voltage output began to fall off after about 15 minutes. The lowered voltage affected all circuits, but mainly the 1L6 mixer tube, whose filament voltage is critical to proper operation. A meter across its filament showed an initial 1.4 volts (normal), which dropped to 1.15 volts after about 15 minutes, at which point the signal became garbled and began to fade. Replacing the rectifier with a new-old-stock selenium type restored the radio to normal operation.

I could, of course, have used a more modern silicon diode as a replacement, but I decided to go with the older selenium type because it was similar to the original part and because I didn't have to worry about reducing the higher voltage of the silicon rectifier. Whichever kind you use, remember to observe polarity: the + side goes to the power supply filter circuit.

[Editor's note: For a history of the Zenith Trans-Oceanics, both the tube- and transistor-types, see the MAARC Newsletter for March 1989, pp. 3-8.]"

Now, if you are a MAARC member, you could go directly to the Members Only section of our MAARC.ORG website and access this article. Want to become a MAARC member? Go to the Membership page on the website. A 1-year membership can be obtained for the low price of $29.

I used a Trans-Oceanic as my project radio when I took the radio repair class offered by the National Capital Radio and TV Museum located in Bowie, MD. I replaced the selenium rectifier in my radio with a silicon diode. For details on that class and the museum, visit NCRTV.ORG.

Who else has a Trans-Oceanic radio. Tell us about it.

Categories Monthly Meetings RadioActivity 2026 Post author By Dave Rossetti Post date February 16, 2026 Thursday, June 4th – Saturday, June 6th, 2026 Annapolis, MD   Theme – “Vacuum Tube Technology”   The Crowne Plaza Hotel 173 Jennifer Road, Annapolis, MD 21401   To download a copy of th...

05/27/2026

A quick post for today, but first we must acknowledge our International Electronics Quiz winner. This was a tough one, but Honorable Mention goes out to Dave Harris.

Now for the post. This one comes to us from ham João Grisi - PY6CJ - who lives in País, Brazil, and provides some interesting history about a WWII British spy radio.

"The SOE Type A Mk III/B stands as a definitive artifact of clandestine engineering, developed by the British Special Operations Executive to facilitate high-stakes communications within occupied Europe. Orchestrated for absolute discretion, this “suitcase radio” was optimized for Continuous Wave (CW) telegraphy, operating across a critical high-frequency range of 4 to 12 MHz.

Technically, the Mk III/B utilized a sophisticated (for its size) superheterodyne circuit. The heart of the system relied on a robust vacuum tube lineup, typically featuring the 6K8 mixer/oscillator and the 6SK7 intermediate frequency (IF) amplifier. To ensure frequency stability during rapid deployments, the transmitter was crystal-controlled, mitigating the risk of frequency drift that could alert enemy direction-finding (DF) units.

Power management was equally ingenious; the unit was designed to run on a variety of alternating current (AC) voltages or external battery packs, often featuring power transformers disguised as everyday objects to bypass Gestapo inspections. This memorandum highlights a design where portability and technical resilience converged, providing the lifeline that coordinated Resistance sabotage and intelligence efforts with London."

Does anyone have anything to add to this WWII spy radio post? Let's hear it.

05/26/2026

Here is an interesting post. About one third of the MAARC members (including myself) are amateur radio operators. Amateur radio is a core component of the vintage electronic hobby. Even those who have never used a tube based radio (which is a relatively high number) or fixed or aligned a more modern solid state radio, still have to dabble in electronics to set up their equipment. Such things as the placement and connection of antennas (either in or near their homes or on their vehicles), providing for electrical power, and integrating their transceivers with various accessories (such as microphones, speakers, headphones, computers, linier amplifiers, antenna rotators, filters, etc.) all require some knowledge of the same basic electronic skills those of us who are emersed in the vintage electronics hobby use on a daily basis. In fact, there are basic electronics questions integrated into the amateur radio licensing exams. That all said, here is a recognition of the importance of amateur radio operators for their contributions to emergency services as issued by Senator Ted Cruz.

"05/24/2026

Senator Ted Cruz, in a strong pre-Memorial Day message, publicly highlighted the critical role that Amateur Radio Service volunteers play during disasters, praising and thanking ham radio operators who provide essential communications when storms and emergencies knock out power and cellular networks and communities are cut off. Sen. Cruz observed that in these emergencies it is ham radio operators who step forward, bringing with them the tools, expertise, and the commitment to reconnect people when it matters most. He noted this dedication was clearly demonstrated in 2017 when Hurricane Harvey’s catastrophic flooding devastated communities across Texas and that it was demonstrated again more recently in the horrific Camp Mystic floods. He emphasized that as the Nation prepares for yet another summer storm season, ham radio’s role remains just as vital as ever.

Watch video now at youtu.be/4ZNeMXyCQ7Y

Stating that while future emergencies will come, Sen. Cruz pointed out that so would Amateur Radio — ready to respond, ready to serve, and to make a difference. He ended his statements, thanking ham radio for its courage and commitment, noting that Amateur Radio’s work strengthens our communities.

Senator Cruz is Chairman of the Senate Committee on Commerce, Science, and Transportation. His comments align with the Amateur Radio Relay League's (ARRL’s) ongoing efforts to strengthen and protect Amateur Radio’s role in emergency preparedness and public service communications.

His comments also reflect growing Congressional recognition of the value Amateur Radio Operators bring to communities across the country. ARRL, The National Association for Amateur Radio®, continues to advocate for legislation that protects and strengthens Amateur Radio’s role in these service activities.

ARRL’s nationwide grassroots campaign supporting the bipartisan Amateur Radio Emergency Preparedness Act has generated more than 155,000 letters to members of Congress in support of H.R. 1094 and S. 459. The legislation seeks to ensure that Amateur Radio Operators can install and maintain effective outdoor antennas at residences where private land-use restrictions might otherwise prohibit them, helping communities maintain resilient emergency communications capabilities during disasters.

ARRL Legislative Committee Chairman and West Gulf Division Director John Robert Stratton, N5AUS, said the continued outreach effort has required “long hours on the ground and an uncountable number of personal meetings with Senators, Representatives, and their staffs” to raise awareness of the importance of Amateur Radio to the nation. “The most recent proof that those efforts have, and are, increasing Congressional support for Amateur Radio is evidenced by the decision of Chairman Cruz to publicly share his personal views on the value and importance of Amateur Radio to the Nation,” Stratton said."

In addition to the Texas disasters acknowledged by Senator Cruz, amateur radio operators were also instrumental in establishing and maintaining communications in September 2024 in response to the devastation caused by Hurricane Helene. This included power, landline, and cellular outages; catastrophic flooding; and landslides to the western part of North Carolina resulting in over 100 fatalities and an estimated $59.6 billion in damages.

Many amateur radio clubs hold weekly communication 'nets' providing experience in coordinated voice communications. A good number of amateur radio operators participate in both the winter and summer 'field day' activities, where they go to various sites, set up their antennas and transceivers, and communicate with fellow amateurs. Many also participate in 'activation' activities where amateur radio operators take a portable radio (the activators) to a specific, often remote or public location to transmit over the air. The goal is to make a required number of contacts with other operators (the chasers or hunters) who are looking to log that specific location. The most popular activation activities take operators outdoors to combine radio communication with hiking, camping, and other outdoor pursuits. These include such activities as:

POTA (Parks on the Air) at registered national, state, and provincial parks to make at least 10 contacts. It’s highly accessible, allowing operators to work from a park bench or their vehicle and track your progress on the Parks on the Air platform.

SOTA (Summits on the Air): A highly active, hiking-oriented program where operators climb designated mountain peaks and operate using portable, battery-powered equipment. SOTA requires activators to make a minimum of 4 contacts from the summit zone.

IOTA (Islands on the Air): An award program focusing on contacts made from islands globally. Activators travel to coastal islands to set up their stations.

Lighthouses (ARLHS & ILLW): Operators set up stations at or near maritime lighthouses to participate in events like the International Lighthouse Lightship Weekend.

In addition, other amateurs participate in various amateur radio emergency services activities that include drills where they practice both voice and digital emergency communications. This can include the ability to send emails over radio frequency (referred to as Winlink) using either high frequency (HF), very high frequency (VHF), or ultra high frequency (UHF) frequencies. All of these various amateur radio activities help in keeping these operators prepared to support emergency services.

Have you either supported or been the recipient of amateur radio emergency services? Tell us about it.

Senator Ted Cruz, in a strong pre-Memorial Day message publicly highlighted the critical role that Amateur Radio Service volunteers play during disasters, pr...

05/25/2026

Today's post provides the answers to yesterday's International Electronics Quiz. Here is some background:

"Test your knowledge of the country of origin of the inventors responsible for these ten inventions by taking this "International Electronics Quiz." It appeared in the July 1967 issue of Popular Electronics magazine, and was compiled by Robert Balin. In some cases the inventor was born in another country but then emigrated to the U.S. or another country before his/her invention or discovery. This is a pretty tough quiz even for someone who has done a lot of reading on the history of technology. Guessing the country of origin for the inventor of the voltaic pile might be easier if you recall the guy's name (hint: his name is in the caption), and for the TV antenna take note of the configuration of the elements (hint: there was nobody named Log Periodic)."

Onto the quiz:

"Recent technological advances in the field of electronics tend to overshadow contributions by earlier scientists from many parts of the world. For example, few students remember that the first known magnetic device - the compass - is a contribution from China, or that the theoretical groundwork in the field of atomic physics which eventually led to the splitting of the atom by the United States, was actually laid by Albert Einstein, the German-born physicist, while doing research work in Switzerland. To test your biographical knowledge of some earlier scientists and their inventions, see how many of the common electrical devices (A-J) illustrated you can associate with the country of origin (1-10) of their inventors."

And the answers are:

1 Belgium - F The first practical industrial dynamo was built by Zenobe Theophile Gramme of Belgium in 1876.

2 Denmark - J The wire recorder was invented by Valdemar Poulsen of Denmark in 1898.

3 England - B The principle of the transformer was discovered by Michael Faraday of England in 1831.

4 France - I The piezoelectric effect in crystals was discovered by Pierre and Jacques Curie of France in 1880.

5 Germany - D The X-ray tube was invented by Wilhelm Conrad Roentgen of Germany in 1895.

6 Holland - G The Leyden jar, forerunner of the modern capacitor, was discovered by Pieter Van Musschenbroek of Holland in 1746.

7 Italy - A The so-called voltaic pile, the earliest battery known, was invented by Count Allesandro Volta of Italy in 1800.

8 Japan - H The "Yagi" antenna was invented by Hidetsu Yagi of Japan in the early 1900's.

9 Russia - C The first electronic television device was actually developed by Boris Lvovitch of Russia in 1907.

10 U.S.A. - E The radio telescope was invented by Karl Janski of the United States in 1933.

How did you do? Did you earn Honorary Mention for the highest score?

05/24/2026

Sunday. Memorial Day Weekend, but still a Sunday. So..., time for a quiz. This one tests our knowledge of vintage electronics history. Here is some background:

"Test your knowledge of the country of origin of the inventors responsible for these ten inventions by taking this "International Electronics Quiz." In some cases the inventor was born in another country but then emigrated to the U.S. or another country before his/her invention or discovery. This is a pretty tough quiz even for someone who has done a lot of reading on the history of technology. Guessing the country of origin for the inventor of the voltaic pile might be easier if you recall the guy's name (hint: his name is in the caption), and for the TV antenna take note of the configuration of the elements (hint: there was nobody named Log Periodic)."

Onto the quiz:

"Recent technological advances in the field of electronics tend to overshadow contributions by earlier scientists from many parts of the world. For example, few students remember that the first known magnetic device - the compass - is a contribution from China, or that the theoretical groundwork in the field of atomic physics which eventually led to the splitting of the atom by the United States, was actually laid by Albert Einstein, the German-born physicist, while doing research work in Switzerland. To test your biographical knowledge of some earlier scientists and their inventions, see how many of the common electrical devices (A-J) illustrated you can associate with the country of origin (1-10) of their inventors.

1 Belgium ___
2 Denmark ___
3 England ___
4 France ___
5 Germany ___
6 Holland ___
7 Italy ___
8 Japan ___
9 Russia ___
10 U.S.A. ___

What do you think? Can you earn Honorary Mention for the highest score? Answers tomorrow.

05/23/2026

Today's post is about mid-1920's home brew crystal radios. It comes to us from "The History Drop" page.

"Imagine sitting in your living room in 1925, gently touching a thin wire to the surface of a rock, searching for that one perfect spot where suddenly, like magic, voices and music flood into your ears.

This wasn't sorcery. It was the crystal radio set (see photo), and for millions of people in the early twentieth century, it was their gateway to a world beyond their doorstep. At a time when factory-made radios cost the equivalent of several months' wages, these homemade contraptions democratized the airwaves.

The genius lay in their elegant simplicity (see schematic photo). You didn't need batteries. You didn't need to plug them into a wall. The radio waves themselves, invisible rivers of electromagnetic energy already streaming through the air from distant transmitters, contained just enough power to drive a pair of sensitive headphones.

Here's how the magic worked: A long wire strung outside your window acted as an antenna, snatching radio signals from the ether. Those signals flowed into a coil (see photo) that let you tune to different stations. Then came the heart of the device, a chunk of mineral crystal, typically galena, a lead sulfide ore you could buy for pennies or sometimes dig up yourself.

Pressed against this crystal was the cat's whisker, a fine springy wire that you adjusted with the delicacy of a safecracker. The crystal and wire together formed a crude diode, allowing current to flow in only one direction. This rectified the amplitude modulated radio waves, extracting the audio signal buried within.

The current was whisper-faint, far too weak to move a speaker cone. But high-impedance headphones were sensitive enough to translate these ghostly electrical pulses into sound. You'd sit there in the dark, one ear pressed to the headphone, the other hand delicately probing the crystal's surface, hunting for the loudest, clearest signal.

Thousands of hobbyists built these sets from scratch, learning the principles of resonance, inductance, and detection by doing. For many, it was their first hands-on encounter with electronics. Some of those tinkerers would go on to become the engineers and inventors who built the modern world of communications.

The crystal set represents something we've almost lost: technology you could understand completely, repair yourself, and build from components you could hold in your hand and comprehend."

Interestingly, the photo that came with the post (see final photo - Image Credit to Elmer Eustice Bucher (Wikimedia Commons) (Restored & Colorized)) was anything but a home brew radio. As best as I can determine, it is a MARCONI TYPE 106-D RECEIVER that was manufactured under license by the Marconi Wireless Telegraph Company of America, dated circa 1915.

Did you ever build a crystal set? Tell us about it.

05/22/2026

Another brief post for today, but first a 'curb alert' about an upcoming auction that you all may find interesting. The Tube Collectors Association listserv had a post regarding a "Huge 45-Year Private Collection of Vintage Electronics & Vacuum Tubes Auction." The online auction, facilitated by Direct Auctions, closes on May 24. Here is what was posted:

"I wanted to share an upcoming auction that I think many tube collectors and vintage electronics enthusiasts here may find interesting. We are hosting a live online auction on May 24, 2026 featuring an incredible 45-year private collection of vintage electronics, including a large selection of vacuum tubes, receivers, amplifiers, military electronics, rare new old stock audio, and much more. This Auction is hosted in Vancouver, BC but the entire auction process can be done online and we do worldwide shipping. You can view the current lots and place pre-bids here:
https://bid.directauctions.com/Mad-Picker-Vancouver-Location-45-Year-Private-Collection-of-Vintage-Electronics-Vacuum-Tubes_as115045?ps=100
Please feel free to reach out if you have any questions. We’d be happy to provide more information where we can. Thank you, Direct Auctions & The Mad Picker"

I previewed the auction, and indeed you may find this interesting.

Onto the post. This one comes to us from the Headphonesty page, and is about Klipschorn speakers.

"When thousands of audiophiles were asked to name the greatest speakers ever made, the Klipschorn, first released in 1946, topped the list and it wasn't particularly close. In fact, Klipsch as a brand dominated the entire poll.

Paul Klipsch (see photo) designed the Klipschorns with a simple but clever idea. Instead of fighting the room, use it. The Klipschorn fires its folded bass horn directly into the corner walls, turning the room itself into an extension of the speaker. That gives it a sensitivity of 105 dB, meaning it can fill a large space with just a handful of watts from a tube amp.

The current model, the AK7, still follows that original vision with some modern driver upgrades added."

The post led to another article that addressed top speakers ranked by audiophiles, and we will highlight some of the more affordable ones over the next few weeks, but here is what it said about the Klipschorn AK6:

"Today’s version, the Klipschorn AK6, stays true to that vision while adding modern upgrades like a sealed back, better components, and a cleaner design. You’ll still need to place them snug in the corners for best results, but once you do, the sound feels fast, dynamic, and huge.

These are also the longest continuously produced speakers in history.

Key Specs:
Design: Three-way, fully horn-loaded corner speaker
Drivers: 15″ woofer (folded horn), horn midrange, horn tweeter
Sensitivity: 105 dB/W
Frequency Response: 33 Hz – 20 kHz ±4 dB
Price: around $14,998/pair (2025)"

Have you owned a pair of Klipsch speakers? Tell us about them.

05/21/2026

A brief post today on early computer history, but first we must recognize our Electronics Angle Quiz winners. Honorable mention goes out to John Wise and Dave Harris for perfect scores. Obviously, they know vintage electronics from all the angles.

Today's post comes to us from the "At The Controls" page as provided by Michel Talbot.

"AVIDAC¹

Pioneer computer scientist Jean F. Hall (see photo) operating the 40-bit Argonne Version of the Institute's Digital Automatic Computer, an early computer built by Argonne National Laboratory in Lemont, Illinois, partially based on a calculating instrument recently constructed at the Institute for Advanced Study at Princeton, New Jersey, the IAS architecture was developed by Los Alamos scientist John von Neumann.

The 2,700 vacuum tube AVIDAC (see photo) was built by the Laboratory's Physics Division for $250,000 and began operations on January 28, 1953 facilitating the solution of mathematical problems of Argonne scientists engaged in reactor engineering and theoretical physics research. The machine had 1024 words stored in 40 Williams–Kilburn tube² electrostatic random-access memory, addition took 10 µs, and multiplication took 1 ms. The 22 kW machine included the following vacuum tube types: 6J6, 5844, 5670 (or 2C51), 5687, 12AU7, 12AT7, and 6AL5. The machine used 20 bits per instructions storing two instruction per word and was a one-address machine with fixed point capabilities using numbers that ranged from -1 to +1 in multiples of 2⁻³⁹. Using bit-parallel adder circuits it could perform at speeds of up to 56,000 additions per second! As with almost all computers of its era, it was a one-of-a-kind machine that could not exchange programs with other computers (even other IAS machines).

https://en.wikipedia.org/wiki/AVIDAC
https://en.wikipedia.org/wiki/Williams_tube

Reference:
Turing's cathedral: the origins of the digital universe by George Dyson, 432p, 2012."

Only used 2,700 vacuum tubes. Sounds like it required quite a bit of troubleshooting.

Any of you ever work as a tech maintaining vintage computers? Bet you have some stories to share.