Category Archives: Vintage Radio

Vintage Radio: How to read a logging scale

Many thanks to SWLing Post contributor, Charlie Liberto (W4MEC) for the following guest post:

Vintage receiver frequency counter…sort of

by Charlie Liberto (W4MEC)

You probably know what a log book is, and maybe a logarithm, but do you know what a ‘Logging Scale’ was meant for? If you are a modern SWL’er, and have a receiver built in the last 40 years or so, you probably don’t have that mysterious 0 to 100 range on your dial, as shown at the top of the picture of the Hallicrafters S20-R main dial, and you may not have a dial at all, peering without question at a digital display of your received frequency.

The Logging Scale on older and vintage receivers had two functions: to let you find a station you might be looking for, when you knew the frequency it would be on, and to determine the frequency of a station, but you had to have known references. How to do that on those old scales that may have had 50 kHz or even 500 kHz hash marks between whole Megahertz numbers, or in that era, KC or MC numbers? The process is fairly straight forward, but did require you to know the operating frequency of at least 2 stations on the band of interest, and the closer they were to the mystery frequency, the better.

Let’s say you are looking for WLMN that is supposed to begin its operation day on 6025 kHz. and your receiver has a mark every 250 kHz between 5 and 7 MHz, that’s pretty iffy as to setting the dial. Now, you know that station WABC is on 5500 kHz, and station GXYZ is on 6525 kHz, so, tuning in WABC you note what number the pointer on the dial is over on the logging scale, maybe it is 40. Then you tune to GXYZ and you find it on 70 on the logging scale. The known difference in frequency between WABC at 5500 kHz and GXYZ at 6525 is 1025 kHz, and the logging scale number difference is 40 to 70 or 30 divisions. Take the 1025 kHz separating your two known stations, divided by the 30 logging scale divisions and you get 34.167 kHz per division. Some more math, the station you are looking for, WLMN is on 6025 kHz, which is 525 kHz away from WABC at 5500 kHz., divide 525 kHz by the logging scale frequency versus division number of 34.167 kHz which equals approximately 16. Take that 16, add it to WABC logging scale number of 40, and you should expect to hear WLMN on logging scale 56 on the dial.

Of course you can flip this process around. If you heard WLMN, but did not know it’s frequency, the same procedure worked backwards to interpolate the logging scale 56 into kHz, added to the WABC frequency/log number, or subtracted from GXYZ numbers, and you would figure out WLMN was on 6025 kHz.

What did this process do? It ‘calibrated’ your receiver dial to known checkpoints by using known frequencies of stations, such that you had a better idea of where you were frequency wise, but it did have it’s limitations. Older receiver dials usually had the lower frequencies divisions of a band close together, and as you tuned to higher frequencies on the same band, hash marks for frequencies got farther apart, while the logging scale stayed linear. This was because builders used the simpler straight line capacitance variable capacitor for tuning, instead of the straightline wavelength or straight line frequency style which would have made the dial more linear. If you used two stations on the low end to set a logging scale reference, chances are it will be quite a bit off in the frequency versus logging scale number on the high end of the dial. So, if you could find two stations that bracketed the one you were examining, that would assure the most accuracy.

After all that, you are probably saying thank God and a lot of engineers for a digital readout.

Thank you, Charlie, for an excellent tutorial and example of using dial logging. I’ve had a number of vintage radios over the years with logging scales and it took some digging to discover how they worked. While digital radios make the process as easy as pie, vintage radios are worth the extra effort!

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Mark spots a vintage radio in “Travelers”

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Many thanks to SWLing Post contributor, Mark Hirst, who adds the following to our growing archive of radios in film. Mark writes:

I’d spotted this radio in the Netflix time travelling series Travelers early on, but it was never in focus to nail a decent image.

In spite of that, it does have a distinctive design that SWLing readers might recognise.

Click to enlarge.

Sitting in the book case next to the stacked books, I’m guessing it’s ornamental rather than functional.

Mark, you obviously have a knack for detecting radios in film! Thank you for sharing!

Post readers: Can anyone ID this radio? I love the design–guessing it’s a Bakelite chassis?

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Seyfi is seeking Harris RF 505A documentation

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Many thanks to SWLing Post reader, Seyfi Genç, who writes:

I’m a strict follower of your blog and of course a SW listener and HAM (TA2MOK) from Istanbul Turkey.

I bought a Harris RF 505A last week for just $30 US!

I need to datasheet to repair it. I didn’t find it on internet.

Thank you.
73!

Wow! You bought an RF 505A for $30? Amazing!

Post readers: If you can help direct Seyfi to RF 505A schematics or a repair manual, please comment with links!

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A carpenter “who carves vintage radio sets”

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Many thanks to SWLing Post contributor, Kim Elliott, who shares the following story from the Odisha Sun Times:

Bhubaneswar: Only a lucky few get to live and breathe their passion and Rajendra Sahu, a carpenter, is one of them.

From Odisha’s capital city of Bhubaneswar, Sahu steals time to give shape to his imagination. He has been carving radios of varied shapes and sizes since past decade-and-half.

“I make radios just because it makes me happy. I return from work by 7 pm and start with the daily ritual of making radio,” said Rajendra. He prepares the cabinet with plywood, sunmica and cane whereas the circuit board is affixed from discarded ones.

“It takes around five days to assemble a radio. I browse through online sites looking for designs,” said Rajendra, who also collects antique radio sets from various parts of Odisha.

“I grew up listening to the radio. There’s a charm to it that the gadgets today fail to deliver. My father too was very fond of them. He would make radios, but I learnt to make them by myself,” he added.[…]

Continue reading the full story at the Odisha Sun Times.

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Doctor Vlado repairs the Panasonic RF-2200 (Part 1)

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Last year, at Hamvention, I picked up a Panasonic RF-2200 for $70. It came with the original box, manual and was in superb cosmetic condition.

The seller told me that over the years he exclusively used the radio to listen to a local FM station.

At that price, I didn’t hesitate to make the purchase even if this would have simply been a non-functioning parts radio for my other RF-2200.

After I brought the radio home, I unpacked it and gave it a quick test.

FM worked brilliantly. Mediumwave and shortwave, however, were essentially deaf. I made the assumption that the ‘2200’s switches and pots likely needed cleaning with DeoxIT. The next day, I was leaving for a two month trip to Canada though, so I packed the RF-2200 back into its box and set it to the side of my shack table.

Fast-forward to yesterday…

While digging around my shack, I re-discovered the boxed RF-2200. Since I was planning to visit my buddy Vlado (the best radio repair guy in the world) yesterday evening, I thought I’d take the RF-2200 and do a proper contact cleaning. Several of the RF-2200’s switches and pots cannot be easily cleaned without removing the chassis.

(Click photos to enlarge.)

Vlado is familiar with the RF-2200 and since it’s not the easiest radio to work on, I asked for his expert hands on the job. Within seconds of handing him the radio, he plugged it in, tested the switches and pots, then removed the back cover (disconnecting the battery compartment leads) and then the front cover (disconnecting the speaker leads).

The magic behind the RF-2200’s classic analog dial:
Vlado offered a word of caution to anyone operating on their RF-2200: as you can see in the photo below, the dial string snakes around the front of the radio and is very close to some key components. You must exercise caution when having a soldering iron tip near the string, or using lubricants nearby.I didn’t realize this, but by the time Vlado started taking apart the RF-2200, he had already determined that even though the contacts needed cleaning, this wasn’t the source of the audio problem for the MW and SW bands.Vlado expertly pulled out the pot for the FM/AM/SW selection–not an easy task–began cleaning it, testing it and re-soldering contacts.

Vlado determined the pot was actually in good shape, thus started testing the rest of the circuit.

After a few minutes of performing tests and getting intermittent performance, he determined that at least one, if not more, of the RF-2200’s caps need to be replaced. Of course, neither one of us was terribly surprised. At this point though, it was getting late and I had an early wake up time in the morning, so I left my RF-2200 with Vlado.

Am I worried about this prognosis? No, not in the slightest…

Doctor Vlado is on the job!

Vlado will have the RF-2200 back on the air in no time, working as well as it did when it was new. He’s actually performed a similar RF-2200 repair for an SWLing Post reader and I’m willing to bet this repair job is relatively simple compared to most he encounters (including the Icom IC-7200 he recently repaired after it was hit by lightening!).

I’ll try to post a “Part 2” update with photos of the RF-2200 repair. Follow the tag: Panasonic RF-2200 Repair

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Dan spots shortwave radios in the film “Operation Chromite”

The Minerva Tropic Master: a portable WWII era morale radio

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If you’re a regular here on the SWLing Post, you’ve no doubt discovered that I’m a fan of vintage radios.

Lately, I’ve been attempting to let go of some of my vintage gear to give my favorite rigs proper shelf space and dedicated antenna time. To keep temptation at bay when I visit flea markets or hamfests (like Hamvention and the one in Shelby, NC) I now focus on WWII era radios; specifically “morale” radios that were used for troop entertainment. I’ve two morale sets: the Scott Marine Radio Model SLRM (technically, a commercial version of a Navy set) and the Minerva Tropic Master.

I purchased this Minerva set off of eBay a couple years ago. I got it for $50 or $60, if memory serves (the seller originally wanted $180 + shipping!). He claimed it worked, but after I asked him a few questions prior to making an offer and learned that “working” meant the speaker prodeced a noise and the backlight worked. I made a low offer and he accepted.

Last year, I took Minerva over to my buddy, mentor and boat anchor doctor, Charlie (W4MEC). Charlie discovered the radio had many issues and several poorly implemented repairs. Still, in a few short weeks, when parts arrived he brought the girl back to life.

With front cover closed.

The Tropic Master is a portable eight tube receiver that covers both the AM broadcast band and shortwave bands from 5.5-18 MHz. It can be powered by AC or DC. It was “tropicalized” to withstand extreme heat and humidity. The internal speaker produces mellow, full-fidelity audio and the volume can be increased to room-filling.

To give you a taste, this morning I tuned the Tropic Master to my in-house AM transmitter on 1570 kHz which was being fed audio from The UK 1940s Radio Station (my favorite Internet radio station). This particular clip features Jay Lawrence’s excellent show, From Stateside:

Click here to view on YouTube.

The Tropic Master is portable and even has a fold down handle on top of the chassis. Though substantial, it must be the lightest of all of my vintage metal chassis radios.

Tuning isn’t exactly precise, but it does the job and is a pleasure to use. It’s quite sensitive on both shortwave and mediumwave. Last night, she was tuned to the Voice of Greece on 9420 kHz–I probably listened to two hours of Greek music while her eight tubes warmed the shack.

Who could turn down a radio with this speaker grill?

If you ever find a Minerva Tropic Master at a flea market or hamfest, I say adopt one! It’s a beautiful receiver and like all good vintage radios has a story and history of its own.

Post readers: Any other Tropic Master owners out there or do you have a morale radio? Have you ever spotted a Tropic Master in the wild? Please comment!

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