Audio Museum May Inspire Your Next Tube Project

Photo1The simple one-story building, home to the Vintage Radio and Communications Museum of Connecticut, provides few clues to the immense, historical collection contained within its brick and mortar walls. The virtual time capsule is filled floor to ceiling with more than a century of technological developments.

But hidden from public view is where the real treasure is for audiophile DIYers. Tucked in the back corner of the warehouse are floor-to-ceiling shelves containing a mind-boggling assortment of vacuum tubes. If you need to repair a vintage radio, television, ham radio, guitar amplifier or hi-fi device, the Vintage Radio and Communications Museum may be just the place for you. The museum has thousands of new and used vacuum tubes available for sale. The tubes are all donated to the museum, and there are more than one museum can possibly display so the overflow is sold to audiophiles all over the world.

The Museum

The museum itself—4,000-square feet of display space—began with its founder, John Ellsworth, and his healthy obsession with history. Ellsworth taught public school for 35 years, beginning with tech education classes in 1975. “That’s when I started going to flea markets and tag sales. One time I saw a small radio, and said to myself, ‘Let’s see if I can fix that,’ and that turned into all this,” Ellsworth explained.  “One day, I realized I had 200 antique radios, phonographs, and other bits laying around the house and thought I had the makings of a museum.”

That was in 1990. Twenty-three years and six locations later, the museum has more than 30 active volunteers who have taken “ownership” of various museum exhibits. “This museum is all volunteer-run, and privately funded,” said Ellsworth. “Our volunteers often start out as visitors. They come back, migrate to what they enjoy, and pretty soon, they are taking care of the portion of the museum.”

“It hasn’t been easy and we have continually had to come up with new and creative ways to fund the museum. But, here in this building that we (and the bank) now own, we have a sense of permanence. And, I really feel the collection—this museum—has really taken on a life of its own.”

In addition to the 4,000-square-feet of displays, there is another 7,000-square-feet of storage space. Every bit of it is filled (in many places from floor to ceiling). “Sometimes the amount of stuff that has been donated to us is a little overwhelming, but we are so grateful to all the people who have contributed,” Ellsworth said.

Potential Audio DIYer Goldmine

Photo3Donated items that are nice but not historically significant are categorized and sold on eBay to help keep the museum’s coffers in the black. The back “storage space” also contains a mini warehouse with an estimated 40,000 to 50,000 new and used vacuum tubes. The tubes, vintage radio equipment, and schematics from the Rider’s and Sam’s series are available for sale. “We are paying the mortgage and keeping the lights on. Things are going okay for us,” Ellsworth said. “We also offer a few classes in radio repair and crystal radio construction.”

The tubes are tested on either a Hickok mutual conductance tester or a Heathkit emissions tester and the volunteers only ship tubes that test a least 70% to ensure that they work properly. The used tubes sell at a 40% discount from the new old stock (NOS) tubes so they’re reasonably priced. All the tubes sold are guaranteed to be in good condition on delivery, with no shorts or leaks.

Electronic Advances

The museum celebrates the history of electronic communications, tracing its development from the mid 1880s to the 1980s advent of home computers. Visitors can send a message in Morse code listen to 100-year-old records on an old phonograph, and learn about the telegraph, telephone, and more.

An entire area is devoted to radios from the 1920s and 1930s and the museum owns some of the first television sets from the 1950s. Among the vintage hi-fi-equipment sits a large glass case filled with vacuum tubes. Across the room, there is a HAM radio room, with a working W1VCM station. Adjacent to the HAM radio station is the DeGeorge Memorial recording studio. The studio, with its amazing array of vintage microphones, can record music and vocals and all formats of audio equipment, enabling transcriptions of vintage sound recordings to modern digital format.

Museum volunteer Dan Thomas, a retired broadcast engineer from Colorado has been instrumental in getting the studio in working order. He is now working on the television display.

“I discovered the museum a little over a year ago. I saw some information about it on the Internet, dropped in one day, and fell in love with it. This is heaven to me,” Thomas said, adding that he spends 15 to 20 hours per week at the museum. “It is fantastic that there is so much history, not only about radio and broadcasting, but also about Connecticut and the surrounding area.”

Chris Kelling, of Manchester, is a HAM radio operator who has volunteered at the museum since 2010. “We have a very active group of volunteers and I’ve met many people who share my interests in communications. We’ve amassed considerable history here, and I hope the museum continues to attract new people.”

Ellsworth often gives narrated tours of the museum. Along the way, groups can view a rare monotype machine, a spring-driven Victrola, and a second-generation Amberol with Edison cylinders stored in its original cabinet. “Back then, the bigger the horn, the bigger the sound,” said Ellsworth.

Within the motion picture section sits a plain wooden box, which Ellsworth said could possibly be the rarest piece in the museum.

“After a great deal of research, we discovered that the box belonged to a traveling production group. They never knew if there was going to be electricity from one theater to the next, so they used this equipment to light the stage. That’s where the term ‘limelight’ actually comes from,” explained Ellsworth. The patent date is the 1870—the stage coach era.”

Ellsworth also discussed Guglielmo Marconi and the invention of telegraphy. But even more intriguing was the story of Reginald Aubrey Fessenden and his broadcast of “Silent Night” on Christmas Eve 1906. “It was the very first radio broadcast,” Ellsworth explained, as he walked passed a huge display aisle filled with radios.

“It original took three different dials to find a station. You had to write down the settings and record them in a log book so you could find it again. You really had to know what you were doing to make it work.”

Back then, the radio was very prestigious, and the pieces were remarkable because many of them were made during the late 1920s. Radios really became central to the home, and the furniture era began in 1927, Ellsworth explained.

Vacuum Tube Potential

Technology, now moving at light speed, shows no end in sight. But, Ellsworth said he is proud of the feelings the museum evokes in his visitors. “It’s amazing. In the beginning, when I started this, if I didn’t do anything, nothing happened. Now, if I do nothing, it will run me over. The museum really has a life of its own. We’ve got something really good here, and we are going to keep it going.”

For audiophiles in need of tubes, the museum has several types available including 6L6, 6V6, 12AX7, 12AU7, 12AT7, 6SN7, 5U4, 5Y3, 6F6, KT66, and 6BQ5 tubes. Although the museum does not yet have an online tubes catalog, there is a form available on its website. Once you fill out a firm, volunteers can contact you regarding availability and Photo2pricing.

Ellsworth said the most popular and the most valuable are the high-end audio output tubes. Our customers come from all over the world, but we sell quite a few to people in Russia, Japan, Australia, and Thailand,” Ellsworth said.

The Vintage Radio and Communications Museum is located at 115 Pierson Lane, Windsor, CT 06095. Call (860) 683-2903 or visit their website for more information. The museum is open year round: Thursday and Friday, 10 AM to 3 PM., Saturday, 10 AM to 5 PM, and Sunday, 1 PM. to 4 PM.

Q&A: Gregory Charvat – Early Curiosity Leads to a Lifelong Engineering Pursuit

Gregory Charvat created an intricate work station at his Westbrook, CT, home to design, test, and build projects.

Gregory Charvat created an intricate work station at his Westbrook, CT, home to design, test, and build projects.

Gregory Charvat—an engineer, professor, entrepreneur, and author—encourages people to explore the opportunities that come their way.

SHANNON BECKER: Your interest in amateur radio equipment began when you were young and continued through your high school years. Can you describe some of your first projects?

GREGORY CHARVAT: I grew up in the metro Detroit, MI, area, and I was very interested in electronics for as long as I can remember, almost naturally. As a young child, I wanted to understand where all the people and things on television came from. One day we took apart an old television set so I could see how it worked.

My mother studied electrical engineering at Lawrence Technological University, which is an engineering school outside Detroit. She occasionally brought me to her classes and labs. Later while she was working at Ford Electronics, she sometimes would take me to work on the weekends, which was super exciting because I was able to make circuit boards, use oscilloscopes, and so forth (this was maybe from age 10–13).

I learned how to use transistors at age 10. I became interested in CB radios. At about the same time, I helped my friends dust off CB radios from their parents’ attics and we built a very nice CB radio network. When I was about 13, I transitioned into amateur radio because my mother wanted me to try a more sophisticated hobby—one where you build your own equipment and  communicate across great distances.

My first electronics projects that I can remember involved building a large switch panel that ran off an old model train transformer to power a car radio, a fan, a light bulb, and other things. Next, I outfitted my bike with buzzers, lights, and a generator to power them with a rechargeable battery. Shortly thereafter, amateur radio became my main interest. I built a 2-m transceiver kit, a 2-m power amplifier kit, modified old police radio power amplifiers to work on 2 m, and many other things. In high school I became involved in a radio telescope project. My role was to upgrade the receiver to a more advanced scanning spectrum analyzer with analog signal-tracking circuits that I developed. Some of these circuits were later used in a friend’s dissertation at Michigan State University.

When I was 16, I interned at Aeroflex Lintek, a defense contractor, helping build radars used to measure the radar cross section of stealth aircraft. From there I became interested in radar technology and I was amazed that you could make images with microwaves. I recall repairing the rotator at Mission Research in Dayton, OH, testing low-noise amplifiers (LNAs) on an HP8510 network analyzer, building many boards, military-specification cables, chassis, mounting power supplies, and finding parts in catalogs for designs.

SHANNON: What is your current occupation? Are you still involved with Butterfly Network?

GREGORY: I am the co-founder of Butterfly Network, which is a privately held company that brings together world-class talent in computer science, physics, and electrical engineering to create an entirely new approach to diagnostic imaging and treatment. I lead the hardware team, which is our company’s largest group. We are responsible for the development of the hardware for the company’s first product.

SHANNON: Can you describe some projects you’ve done?

GREGORY: I built the first three prototypes, set up our lab and machine shop, recruited more than half the company, negotiated a number of contracts, and now I am learning about application-specific integrated circuit (ASIC) engineering. We are looking for an analog ASIC engineer and a chip packaging engineer, for anyone who is interested in working with me. I can be reached at I will reply to all e-mails.

SHANNON: Are you still instructing at the Massachusetts Institute of Technology (MIT)? Can you describe the courses you teach?

GREGORY: My Build a Small Sensor Radar course continues to this day. In June, it was offered as an MIT Professional Education course. Numerous universities have adopted this course as either a capstone engineering project or full-semester course. Private institutions and government labs have also adopted the course for internal training. The coffee-can radar project has even made an appearance on Mongolian National Television as part of an MIT EdX program a friend of mine ran last summer. You can now buy the coffee-can radar project as a complete kit from Quonset Microwave.

Additionally, two other Build a Radar courses were developed from the original course including Build a Phased-Array Radar and Build a Search and Track Radar, but I am no longer teaching these courses. My relationship with MIT has evolved into me being an advisor for the Camera Culture Group at the MIT Media Lab where we experiment with two interesting technology threads.

SHANNON: You have a main website, a blog, Mr. Vacuum Tube; several YouTube videos; and an active Twitter account. What types of projects do you typically share?

GREGORY: I like to read other people’s Twitter posts and blogs and I watch  YouTube videos. I appreciate the time and effort other enthusiasts put into sharing their work. To this end, I like to share what I am doing and maybe it can help someone someday. For this reason I try to share everything I can, from symposiums that I am involved in to topics in my book, to papers I am publishing to hobbyist projects (e.g., vacuum-tube audio, antique radio restorations, clock and watch restorations, and sailing adventures).

As an undergraduate, I learned from a math professor friend of mine that you must publish everything you create, otherwise the knowledge will be lost.

SHANNON: You are a Senior Member of the Institute of Electrical and Electronics Engineers (IEEE). What does your involvement entail?

GREGORY: I’m a huge fan of the IEEE. The IEEE organization maintains high academic standards for papers in its journals and symposiums and I really appreciate that. IEEE members are the archivists and storytellers of electrical engineering history, past and present. To help out, I was chairman of the IEEE Antennas and Propagation Society Boston Section for two years. Our meetings went from 12 attendees each month to 40 by my tenure’s end. This was achieved by the use of social media and the lineup of fascinating speakers. I then became a Member-at-Large for the IEEE Boston Section’s Executive Committee in 2012. Additionally, I was on the steering committee for the 2010 International Symposium on Phased-Array Systems & Technology. I am currently on the steering committee for the 2013 symposium this fall in Waltham, MA.

SHANNON: You have authored many articles, including a two-part audioXpress series, “Vacuum Tube Home Theater System” (May–June, 2012), about building a “monster” system with 23 vacuum tubes. Tell us a little about the system. Have you made any upgrades or adjustments?

GREGORY: This system was originally developed in the summer of 2001 while I was a junior undergraduate. It was deployed in my dorm room. The feedback compensation networks were upgraded in 2003. The power supply was upgraded in 2005 and I moved to a direct grid-bias configuration to get more power out of the amplifiers.
In 2009, I again upgraded the feedback compensation networks. This system is in our living room and it is used almost every day. It is currently in a maintenance posture, where I occasionally have to replace one of the original tubes from 2001. Recently I had to replace a high-voltage rectifier diode. I’m due to replace the pentodes on the subwoofer amplifier within the next few weeks.

SHANNON: Your forthcoming book, Small and Short Range Radar Systems, is slated for publication in February 2014. What can readers expect to learn?

GREGORY: This will be the first book on small and short-range radar devices. My goal for the book is to show readers how they work, how to build something practical, and do it quickly.
I want to show readers the high-level basics and how to do a back-of-envelope estimate to determine if a system is worth developing. I also wanted to provide working engineering examples of each type of short-range radar, including complete schematics, diagrams, bill of materials (BOM), a demonstration video, data for the reader to process from that video, and usable MATLAB scripts. I also discuss the practical aspects of design so these examples can be scaled to other applications or expanded.

As engineers, we are applied scientists. We use our understanding of physics to build something tangible to help humanity. This book facilitates that process for short-range radar sensors.

Gregory’s go-to vacuum-tube transceiver is a 20-m single-sideband (SSB) of his own design.

Gregory’s go-to vacuum-tube transceiver is a 20-m single-sideband (SSB) of his own design.

SHANNON: Tell us about the amateur radio station you designed.

GREGORY: After hearing stories about a friend of mine at the MIT Haystack Observatory, who as a teenager built his own radio out of one type of transistor his father was able to “borrow” from work, I decided to redo this exercise myself. I developed a shortwave receiver out of one type of transistor. It was a fascinating experience.
From there, I decided to develop my own single-sideband (SSB) transceiver design from scratch. I built a 20-m SSB radio with 40-W peak-envelope power (PEP) that is extremely sensitive. It was an amazing experience to contact Western Europe with a radio that I developed myself!

Shortly thereafter, the American Radio Relay League (ARRL) issued the Homebrew Challenge III, to build a 10-m and 6-m SSB/CW transceiver for less than $200. I took this challenge and submitted a working radio one day before the contest ended. Apparently mine was one of only two submissions. The other was late, but I blew the budget at $450! (It’s really about the experience, not the cost.) I was given honorable mention and an article in QST magazine for my efforts. More importantly, I had the pleasure of getting to know some of the folks at ARRL.

Most recently, I developed a way of tying a SSB transmitter to an R-390A, which is the tube era’s best communications receiver and highly sought after by collectors. An article on this modification will run soon in QST’s “Hints and Kinks” column.

In summary, my homemade amateur radio station consists of a 20-m SSB radio, a 10-m and 6-m SSB/CW radio, and an R-390A that is tied into the 20-m radio for when I want to run in “boat anchor” mode.

SHANNON: If you had a full year and an ample budget to work on any design project you wanted, what would you build?

This homemade amateur radio station evolved from an idea to construct a shortwave receiver out of one type of transistor.

This homemade amateur radio station evolved from an idea to construct a shortwave receiver out of one type of transistor.

GREGORY: If I had a free weekend in the summer I’d sail to Long Island, NY. If I had a free weekend in the fall, winter, or early spring I’d restore a vintage mechanical wristwatch. If I had a free week I would restore the vintage all-tube Telefunken stereo receiver in my office. Or, I’d combine a 1970s solid-state amateur radio transmitter with my R-390A. If I had one to four months, I would bring to close the projects I am helping with at MIT’s Media Lab.

After that, I would look for something long term. I would probably brainstorm with some friends about a new idea for a fun research project or a startup. Generally speaking, I would like to have one long-term project moving steadily along while also closing numerous shorter-term projects along the way.

Simple Circuits: Turn a Tube Radio Into an MP3 Amp

Want to give your MP3 player vintage tube sound? You can with the proper circuits, an antique radio, and a little know-how. In addition to generating amazing sound, the design will be an eye catcher in your home or office.

Here I present excerpts from Bill Reeve’s article, “Repurposing Antique Radios as Tube Amplifiers,” in which he provides vintage radio resources, simple circuit diagrams, and essential part info. He also covers the topics of external audio mixing and audio switching. The article appeared in the May 2012 edition of audioXpress magazine.

Manufactured from the 1930s through the 1960s, vacuum tube radios often contain high-quality audio amplifiers at the end of their RF signal chain. You can repurpose these radios into vintage, low-power tube amplifiers—without marring them in any way or detracting from their original charm and functionality as working analog radios.

Wood-cased radios have especially good sound quality, and the battery compartments in antique “portable” radios (like the Philco 48-360 or the Zenith Transoceanics) provide perfect locations for additional circuitry. When restored properly, large furniture-style radios that were built for “high fidelity” (like the late 1930s and early 1940s Philco console radios) can fill a room with rich beautiful sound.

Simple Circuits

The simple circuits described in this article perform two functions. They mix an external line-level stereo signal (typically from an MP3 player or computer) and reference it to the radio’s circuit. They also use the radio’s on/off knob to switch this external signal to the radio’s audio amplifier.

There is not one circuit that will work for every antique radio. (Original schematics for antique tube radios are available on the web But the circuits described here can be adapted to any radio topology. All the parts can be ordered from an electronics supplier like Digi-Key, and the circuit can be soldered on a prototyping printed circuit board (such as RadioShack P/N 276-168B).

External audio mixing

Figure 1 and Figure 2 show some examples of circuit schematics that mix the line-level stereo audio signals together (almost all tube radios are monophonic), while providing galvanic isolation from high voltages within the radio. Figure 1 shows an inexpensive solution suitable for most table-top radios.


Figure 1: An inexpensive circuit for mixing an MP3 player’s stereo audio signals safely into an antique radio. None of the component values are critical. (Source: B. Reeve, AX 5/12)

These radios have relatively small speakers that are unable to reproduce deep bass, so an inexpensive audio transformer (available from on-line distributors) does the job. I picked up a bucket of Tamura TY-300PR transformers for $0.50 each at an electronics surplus store, and similar transformers are commercially available. Alternatively, the Hammond 560G shown in Figure 2 is an expensive, highquality audio transformer suitable to high-fidelity radios (like the furniture-sized Philco consoles). A less expensive (and fine-sounding) alternative is the Hammond 148A.

Figure 2: A high-fidelity circuit for mixing external stereo audio signals safely into an antique radio. (Source: B. Reeve, AX 5/12)

I use Belden 9154 twisted, shielded audio cable for wiring internal to the radio, but twisted, 24-gauge wire will work well. An 8′ long audio cable with a 3.5-mm stereo jack on each end can be cut in half to make input cables for two radios, or you can use the cord from trashed ear-buds. You can route the audio cable out the back of the chassis. Photo 1 is a photograph of a 1948 Philco portable tube radio restored and used as an MP3 player amplifier.

Photo 1: A 1948 Philco portable tube radio restored and repurposed as an MP3 amplifier. (Source: B. Reeve, AX 5/12)

Audio switching using the radio’s on/off knob

After creating the mixed, radio-referenced signal, the next step is to build a circuit that switches the voltage driving the radio’s audio amplifier between its own internal broadcast and the external audio signal.

Figure 3 illustrates this audio routing control using the radio’s existing front panel power knob. Turn the radio on, and it behaves like the old analog radio it was designed to be (after the tubes warm up). However, if you turn the radio off, then on again within a few of seconds, the external audio signal is routed to the radio’s tube amplifier and speaker.

The circuit shown in Figure 3 uses a transformer to create the low voltage used by the switching circuit. There are many alternative power transformers available, and many methods of creating a transformerless power supply. Use your favorite….

The next photos (see Photo 2a and Photo 2b) show our additional circuit mounted in the lower (battery) compartment of a Zenith Transoceanic AM/shortwave receiver. Note the new high-voltage (B+) capacitors (part of the radio’s restoration) attached to a transformer housing with blue tie wraps.

Photo 2a: The inside view of a Zenith Transoceanic AM/shortwave radio restored and augmented as an MP3 audio amplifier. b: This is an outside view of the repurposed Zenith Transoceanic AM/shortwave radio. (Source: B. Reeve, AX 5/12)

The added circuit board that performs the audio re-routing is mounting to a 0.125″ maple plywood base, using screws countersunk from underneath. The plywood is securely screwed to the inside base of the radio housing. Rubber grommets are added wherever cables pass through the radio’s steel frame.—Bill Reeve

Click here to view the entire article. The article is password protected. To access it, “axreeve”.

A Workspace for Radio & Metrology Projects

Ralph Berres, a television technician in Germany, created an exemplary design space in his house for working on projects relating to his two main technical interests: amateur radio and metrology (the science of measurement). He even builds his own measurement equipment for his bench.

Ralph Berres built this workspace for his radio and metrology projects

Ralph Berres built this workspace for his radio and metrology projects

“I am a licensed radio amateur with the call sign DF6WU… My hobby is high-frequency and low-frequency metrology,” Berres wrote in his submission.

Amateur radio is popular among Circuit Cellar readers. Countless electrical engineers and technical DIYers I’ve met or worked with during the past few years are amateur radio operators. Some got involved in radio during childhood. Others obtained radio licenses more recently. For instance, Rebecca Yang of chronicled the process in late 2011. Check it out: and

Do you want to share images of your workspace, hackspace, circuit cellar, or audio workbench with the world? Click here to email us your images and workspace info.