Greetings to All
We are now in the ninth month since the world changed. In thinking back to the first months of 2020, I remember in early March when we were preparing for the BARC hamfest, there was talk about a strange virus that had been found in a very few other states, but at that time there was none known in Alabama. What has transpired from that time until today is history. It has been a time of disbelief, fear, panic and to say the least, a time of confusion and uncertainty. We have seen the gamut of stories and advice: mask - no mask, lock down - no lockdown, stay at home - live life normally. I am very pleased at this time to say that all of our members are doing well. I am not aware of any virus related issues with any of our members or family members.
Society activities continue to move along, although slowly. There has been fair attendance at the Shop on meeting days. Some are working on personal projects in the shop and at home. The Alabama Power headquarters continues to operate remotely and our museum in that building remains closed. No word yet when that might change. The future is still uncertain at this time as we move into the winter months. We just have to move forward and “keep the faith”.
The quarterly financial report from Treasurer Mike Woodruff, indicates all the bill are paid and revenue was received from the recent radio auction. Also, on the financial horizon, on January 1, 2021, annual Society dues are due. Besides the usual ways of paying your dues by mail or bring them to the Shop, you can now pay your dues online. Just go to the Society website at alhrs.org and click on the Membership tab at the top of the page, them scroll down to the Online Membership Application & Renewal line. Click on the tab and you can now enter your information to make your payment by Paypal or credit card. We have also added a tab under the Donate tab for those wishing to make a monetary, tax deductible donation to the Society.
Last Saturday the Society held an auction at the Shop which was very successful. We will have more on the auction later in this newsletter.
Recently the officers of the Society were invited to a Zoom meeting with officers of other radio clubs across the United States, to discuss subjects of mutual interest. We will have more on this historical event in next month’s newsletter.
Thanks for allowing me to share some of my personal thoughts with you. If you are working on a project at home and need help, I am available by phone or email, at any time.
May God bless you with health and safety!!!
See you at the Shop, when we can.
AHRS Radio Auction November 7, 2020
Auctioneers Ray Giles & Tom Killian, with technical assistance from Boyd Bailey, held an auction at the regular Saturday morning session at the AHRS Shop. About 20 members attended in-person and about five members by Zoom, on-line. The auction was very successful. All items were sold except for the Onkyo receiver, which did not receive any bids. Due to the success of this auction, Ray advised he is considering another auction for December. Stay Tuned!
From Dee Haynes
We still have a few Super Probe boards and components left.
Please get in touch with me if you are interested in putting one
of these probes together. Be the first one on your block to have
a Rick-a-Dee Super Probe. There is no charge for these boards
but we will accept a small donation. You may email me if you are
interested at firstname.lastname@example.org Simply cut and paste this address
to your email.
In Rush Current Limiting in Vintage Radios
Submitted by: Tom Desaulniers
Greetings to all who are reading this epistle. I am proud to be associated with such an august group as the Alabama Historical Radio Society. I have known quite a few of you for a long time. As you know, I have been messing around with this stuff since I was about 12 years old and was a good friend of Lee de Forest. Yes, I’m almost that old.
Anyway, over the years I have replaced a great many vacuum tubes (valves). I worked most of my college time in a TV shop where all the radios and TVs still had tubes and have noticed that the majority of them died as a result of filament failure, more so than getting weak or gassy. All of the radios I have had that were fitted with a pilot lamp showed a startling characteristic that worried me. That is, when you first turn them on, the pilot lamp goes full bright, and then it dims a bit before coming to full brilliance again. This got me to wondering about the huge inrush current and the possible culprit causing the tube failures.
So, I got out my trusty old clamp-on amp meter, and using the 10 to 1 “magnifier” attachment, proceeded to watch the amp draw on two of the antique radios I have. These are all radios that use 12SK7, 12SQ7, 12SA7, 35Z5 and 50L6 type tubes (or similar). The filament current (after warm-up) is rated at 150 ma and, when running, the current draw shows to be around 240/250 ma, that includes the DC load drawn after warm-up. However, the inrush was in the order of nearly a full amp for a second or so. Geee. That’s quite a hit for such a delicate thing like the tiny little filament in these tubes.
After a glass of wine one evening I got to reminiscing about my college days (1965 through 1970), and I remembered looking at a schematic for one of the first Japanese transistor radios that were beginning to trickle in then. I remember seeing something that was new to me. Hmmm. What in the world was a thermistor? It turned out that those first radios had a bad habit whereby the audio output transistor didn’t like getting too warm and would run away and commit suicide. So the Nipponese put a thermistor in the emitter lead to control collector current if it went too high. OK, that’s cool.
After much creaking and groaning, my mind wandered back to my antique radio’s inrush and I wondered if a thermistor might be of some help here. I got on Google and looked up thermistors. That led me to a company called AMETHERM. They are located in Carson City, NV and their phone number is 775-884-2434. Turns out they are one of the leading companies making things called (of all things) inrush current limiters. Man, how lucky can I get? A man named Mehdi Samii spoke to me and I was blown away. This man is a genius and seems to know everything worth knowing about inrush limiters. He spoke with a heavy accent, but by golly, when I explained what I was thinking about, he INSTANTLY understood what I needed and recommended several of their products and gave me the part numbers and said they were all available at Mouser Electronics. It’s Christmas in October!!!
I tried several of the numbers he gave me and they worked “OK,” but not quite as well as I hoped. I started looking at their spec sheets and picked a couple more that were a bit bigger in diameter. That was the trick. Bigger diameter meant slower time to target resistance due to greater mass. I digress here to explain these are NTC, (Negative Temperature Coefficient) devices. That is, unlike regular resistors that INCREASE in resistance when they get hot, actually change to LOWER resistance as they get hot. So I finally used their number SL-22 12102. This one starts out a 120 ohm at room temperature and slowly gets warm and finally reaches about 6 to 8 ohms. (It is about 7/8” diameter and about ¼” thick). That low resistance after warm-up means little with 120 to 125 volts coming in and a final current draw of 250 ma. Actually, that might be a good thing, as they drop a few volts, which is a good thing for radios that were designed for maybe 115 volts. They are good for up to 2 amps, and I don’t think many radios pull even close to that (but I may be wrong there).They eventually warm up, but not enough so you cannot keep your fingers on them for a few seconds, and I don’t think that would cause any heat problems under the chassis.
Anyway, now when I turn my old geezer radios on, the pilot lamp starts out at a very low brilliance of a dull orange, then goes dimmer for about 20 seconds, then slowly comes up to full brilliance after about a minute and a half. Not a big time price to pay for saving “shell shock” to those magnificent “field effect devices, in a silicon dioxide case, with a built in pilot light” (my definition of a vacuum tube).
Many of these radios have the power switch in the chassis side of the line, that is, they ground one side of the AC line to the chassis when you turn it on. I figured that would be the easiest place to put the thermistor. However, it turns out, that causes a mighty hum to develop. It could be because it introduces some resistance basically in the negative lead of the filter capacitors or maybe because it is in the lead closest to the filament of the 12AQ7 (a very sensitive tube) which might induce some hum due to heater/cathode capacitance. Who knows? But I eventually put mine in the other lead using a standoff insulator terminal strip (see photos). I’ll put two videos on line with “Before” and “After” short videos of the pilot light turn-on brilliance.
Here is a link to my Google Drive folder containing two photos of the underside of the chassis where I installed the thermistor, a video of the pilot light before and another after the installation and finally a video of the radio running at night and me running the dial. Enjoy.
By the way, the Mouser part number is 995-SL22 12102. There is a SPACE between the 22 and the 12. The URL for the data sheet is https://www.mouser.com/datasheet/2/600/SL2212102-587864.pdf
Submitted by: Jim Rogers
I received a copy of Nuts and Volts magazine from a friend in Florida. In the magazine there was an article about. “Radio Fax”. It would seem that in the 1930-1940 era, radio broadcasters and some newspapers thought it would be nice to have the newspaper ready to read in your home over your breakfast coffee. The radio broadcasters and the newspaper got together and after the stations ended their broadcasting day at midnight, they would transmit the weather updates and news by radio fax. From searching the subject on the internet I found RCA was a major implementer of this technology. It was to be featured at the world’s fair, right alongside television. So went radio fax. Television won the public eye and the rest is history. A fax receiver in those days cost about $300 or in todays money about $3500.
Saturday meetings have been suspended due to the coronavirus.
We meet every Saturday (unless a Holiday weekend) at 9:00 a.m., at the one-story AHRS Shop at the corner of 8th Avenue North and 18th Street, (1801 8th Avenue North, Birmingham, AL 35203). Birmingham, AL 35203). Use the rear (Southeast) entrance.
Tuesday meetings have been suspended due to the coronavirus.
The Shop is open on Tuesdays at 9:00 a.m. until around 11:30 a.m. when we go to Marilyn's Deli and Dog for lunch next door. Note that parking can be a problem on Tuesdays, so you may have to find street parking occasionally.
Regular meetings have been suspended due to the coronavirus.
We meet on the fourth Monday night of each month, too, at 7:00 p.m. Please come join us!
Due to the coronavirus, classes are presented on Zoom sessions. Check your email for times and dates and information to join the Zoom session.
One more great benefit from becoming a member of AHRS--free Electronic classes!
Classes are taught the first Saturday of each month (except when something special is taking place, then we agree on what Saturday).
We start from the beginning Ohms Law, inductors, resistor and Capacitors color codes, as well as what each component does within the radio circuits. We also teach how to use test equipment used in the repairing of radios. We teach troubleshooting radio troubles, as well as how to read a radio diagram. There are coil winding classes, and one-on-one repair help. Come join these classes!
Membership dues are $25 a year, payable beginning in January. If you have questions about your dues, you can contact Treasurer Mike Woodruff at 205-823-7204. Dues can be mailed to AHRS at P.O. Box 131418, Birmingham AL 35213.
Be sure and check out our website at https/www.alabamahistoricalradiosociety.org, which has copies of all newsletters from 2006 to the present (click on News), videos, photo galleries, museum, Old Time Radio columns, Projects, Reading Rooms, Archives, and Contact Information
President – Dave Johnson
Vice President – Steven Westbrook
Recording Secretary – Dee Haynes
Treasurer – Mike Woodruff
Boyd Bailey, member and Instructor 334 412-6996
Website – David Lake
Newsletter – Jim Rogers