Mid-Atlantic Antique Radio Club - MAARC

01/04/2025

Not a Tidbit, but a nice brief article by long time MAARC member Ed Lyon from the July 1996 edition of Radio Age on Isolation Transformers:

"Isolation transformers are essential components in your test
equipment inventory, if you service old radios or television sets. These are 1-to-1 transformers which take in 120 volts ac from the
power line and deliver 120 volts ac to a convenient socket into which the radio to be serviced is plugged. The purpose is isolation of the radio under service from the power line system and its ground connection.

The reason for this isolation is to keep the radio's chassis and internal voltage supply connections from being connected to the power line system, so that they may be touched safely by the hands or connected safely to test equipment.

These transformers are available as old stock in various power ratings from 35 watts to 500 watts, the latter being huge and heavy. They are also available new from antique radio parts houses, but
Radio Age - July 1996 they are expensive. Many of today's radio
servicemen (and women) have had to fashion their own isolation transformers out of surplus transformers found at hamfests and flea markets. One suggestion at the restoration seminar at Radioactivity
- 96 was to use two identical high-powered filament transformers, connected back-to-back. A tip is to select relatively high voltage filament transformers, like 12-volt or 24-volt units, rather than 6-volt transformers. This keeps the filament winding from having to carry large currents. A 50-watt isolation transformer design would require the use of 15-ampere 6-volt transformers.

Another tip: do not provide a duplex convenience socket as the isolation transformer output, as it is too tempting to plug two radios or devices into it, with dangerous consequences - no isolation between them."

We see used isolation transformers available for purchase at our monthly MAARC meetings, usually at very good prices. They are absolute necessities to use if you are working on a "hot chassis" device, where the chassis is connected directly to one side of the AC power.

Anyone have any additional advice to provide our followers regarding isolation transformers?

01/03/2025

Here is a little Tidbit from the April 1996 edition of Radio Age that may be of interest to you.

"Letter to the Editor from Pete Peterson, Bellevue, WA:
I read with appreciation the articles in your February 1996 issue, but found an error in the "Germanium Radio" article by Ludwell Sibley. The first paragraph indicates that crystal set operators were freed from the need to adjust galena detectors after the 1N34's introduction in 1946. Fixed detectors were available much earlier.
My radio collection contains two Falck receivers, built in about 1925 and L927, which employ fixed crystal detectors in sealed housings mounted on the four-tube chassis.

The Falck usage was not unique. Fixed crystal detectors, using various minerals but mostly galena, were generally available in that era. I recall using both adjustable and fixed detectors when I started making crystal sets as a boy in 1939 or 1940. I remember nothing about details, brand names, or sources except that I bought one type of fixed detector from a supplier who had a classified advertisement in Popular Mechanics.

[LudweII Sibley verified that he was well aware of fixed crystal detectors being available much earlier than 1946, but the traditional crystal set from the early days of radio relied on the ubiquitous cat's whisker arrangement, and it was to that traditional set that his comment referred. - Editor.]

I have to remember that when you hit return in the comments, it sends the comment. I had to go back and edit my previous comment, which is a trick I was not even aware you can do.

Do any of you have memories of building of using an early crystal set? Tell us about it.

Just an FYI, if you are a MAARC member, then you know you can access PDF copies of all our Radio Age articles back to 1975 through the Members Only section of the website, MAARC.ORG. If you are not a MAARC member, you may want to check us out. You can find out details about membership on the club website. Here is the link to the Membership page: https://maarc.org/membership/. MAARC has 600 members, the majority of whom do not live in the Mid-Atlantic region. They maintain their membership because they love to read the Radio Age articles.

01/01/2025

Happy New Year MAARC followers. Thought we might try something new for 2025.

Our Radio Age journal started a section entitled Tidbits when MAARC took over the printing responsibilities in 1994. Many of the Tidbits addressed club items of interest, while others addressed service tips. Here is one from the April 1995 edition of Radio Age:

"Hint found in a 1940s radio service magazine: A 6K6 tube can replace the much more scarce 6N6 tube with no socket rewiring or other changes." The editor followed up with "Didn't have time to check this one out--use at your own risk - Editor"

What do you think?

The 6N6 is a Direct-Coupled Power Triode, a heater type output tube comprised of two triode units mounted in a common bulb. The smaller (or input) section acts as driver for the larger output unit and is directly coupled to it. The input cathode and output grid are connected internally. The tube operates without bias so there is no need for a cathode resistor and it's associated by-pass condenser. Since the output section operates with a positive bias, it requires a high-µ characteristic to keep the plate current low. This is achieved by using two separate control grids connected in parallel inside the bulb.

The 6K6 is a Power Pentode.

Socket wise, the two octal tubes had the same pin settings, with the exception of pin 4, which went to the Plate 1 for the 6N6, and the Screen Grid for the 6K6.

What say you. Do you thing the 6K6 would function as a direct plug-in substitute for the scarcer 6N6? We would like to hear your thoughts.

12/25/2024

Merry Christmas and Happy Hanukkah to all our MAARC followers.

Over the next few months you will see some subtle changes to both our page and our MAARC.ORG website, to include our increased focus on modern day tube audio and vintage computers. We are also working on the ability to accept online membership sign up and renewal payments.

Enjoy the holidays, and keep your tubes warm.

December 15 @ 10:30 am - 4:00 pm EST December 2024 Monthly Meeting Sully Station Community Center 5101 SEQUOIA FARMS DRIVE, CENTREVILLE, VA, United States Tailgating at 10:30 a.m., Walk-around auction at 12 p.m., Meeting at 1 p.m., Main auction at 2 p.m. Display table: Ham transmitters weighing less...

11/17/2024

November 17th MAARC Meeting

09/28/2024

September meeting of the Early Television Museum, tonight Saturday 9/28, 8:00 PM.
Topic: Test Equipment: Antique Meters
Our September Meeting will feature four segments: first, Steve McVoy will update news of the Early Television Foundation, followed by a look at an item in the museum's collection. Mike Molnar will give a presentation on early electrical meters. Then we will have an open topic discussion. Feel free to introduce any topic you are interested in.
Zoom Login information:

early television

08/31/2024

August 31 Early Television Museum meeting

early television

08/18/2024

06/29/2024

June Online Meeting of the Early Television Museum
Saturday, June 29 at 8 PM EDT
Our June meeting will feature four segments: first, Steve McVoy will update news of the Early Television Foundation, followed by a look at an item in the museum's collection. James O'Neal will make a presentation about "Why We Have Fractional (Non-integer) Television Frame Rates". After his presentation, he and George Lemaster will be available to answer questions, and George will briefly discuss the non-integer field and frame rates in NTSC. Then we will have an open topic discussion. Feel free to introduce any topic you are interested in.
Zoom logon information at www.earlytelevision.org
Don't forget to get your tickets for the 2024 Sweepstakes - Grand Prize is a fully restored Philco Pedestal Predicta. Proceeds support the museum.

early television

05/25/2024

Tonight: May Online Meeting of the Early Television Museum.
SATURDAY, MAY 25 AT 8 PM EDT
OUR MAY MEETING WILL FEATURE FOUR SEGMENTS: FIRST, THERE WILL BE A REPORT ON NEWS FROM THE EARLY TELEVISION FOUNDATION, FOLLOWED BY A PRESENTATION ABOUT AN ITEM IN THE MUSEUM'S COLLECTION. THERE WILL THEN BE A REPORT ON THE 2024 ETF CONVENTION, FOLLOWED BY AN OPEN TOPIC DISCUSSION. FEEL FREE TO INTRODUCE ANY TOPIC YOU ARE INTERESTED IN. Logon information at

early television

04/21/2024

Presentation was on the history of beam power tubes.

02/18/2024

MAARC Meeting for February 18, 2024 in Davidsonville, MD.
Program: Super Show and Tell

01/28/2024

Davidsonville meeting for January 28, 2024.
Program: Wyatt Circo - Plastics: How to Identify, Clean, Care for, and Preserve Different Types of Radio Plastic

01/24/2024

The January 27 online meeting of the Early Television Museum will be an introduction to 1" video tape recording. John Turner will conduct this follow up to his earlier presentation about 2" recorders. John will demonstrate the operation of some machines in his lab. Join us on Zoom.
Info at www.earlytelevision.org.

Early Television Foundation

early television