1920s battery radios....how do they work?
 

Decided to take a leap backwards in my learning and try to understand how a 1920s battery radio works....and thereby learn to repair them and even soup them up a bit if possible :)

Let's take this 1925 Resas Tone-A-Dyne.....I now have two of them. Since I can't seem to get any form of schematic on it (and even if I could, 1920s radio schematics are horrible compared to the Sams I've been spoiled on using with TVs), I'm having some difficulty understanding how the radio works.

Let me start by saying that I do understand the A, B, and C voltages and what they do, and both radios do work. They use five 01A tubes. No real parts inside except the coils, two transformers (no idea what they do), and one plug-in 1.5 meg grid leak resistor (again, no idea what it does).

Resas #1 works fine, but the volume and frequency tend to drift around a little and it requires adjustment every few minutes. Resas #2 is much more stable, but the audio is more muffled. Since I operated both on the same set of 01As, this leads me to believe that there are components I can replace to get them performing better.

The 1.5M grid leak resistor on Resas #1 measures 2.6M, so that needs replacing. The one on Resas #2 measures out at 1.7M, so that's closer. What a grid leak resistor does I'm not sure.

Picked up a restored Atwater Kent big box model 20, and that thing makes the Tone-A-Dynes sound like the dog's blanket....so either the A-K is just a superior radio, or the Resas(es) need work.

Incidentally, I started figuring out how to tune them by hooking up a signal generator and dialing them in with it, then cutting the power when I found the desired frequency. Since all of these radios seem to love being hooked up to the signal generator and get much better reception when hooked up to it even when it's off, until I get a larger antenna I just run them that way :)

Any insights and advice are always appreciated! :)

http://videokarma.org/attachment.php...0&d=1491132540

TRF sets are basically an LC filter tune-able over the AM band followed by a stage of amplification (rinse and repeat a stage or three), a grid-leak detector (google for more on that I forgotten how those work), and an audio amp stage or two.

Regenerative sets are a complex way of making minimal tube count work like a big TRF....Basically the RF is fed back in a positive feedback loop to J-U-S-T shy of the point where it oscillates (you'll know when it does)...IIRC some managed detector/audio gain function from the same single tube.

There were also other schemes like one where there was a single detector tube and the TRF stages did double duty as audio amps.

There were a few more designs, but my knowledge is rather limited. 20's sets have always been stupid expensive, hard to get parts for, and hard to power putting them out of my reach. I've owned/worked on 3 early AC powered TRF sets, and just got my first restorable bat set a week ago.

Grid leak is used to minimize tube capacitance problems.

Tube capacitance problems were addressed by neutralization (negative feedback), as in the Neutrodyne scheme. A bit later, an xtra grid was added between the G1 and plate (screen grid) to minimize G1-plate capacitance, as in the famous 24A tetrode.

Grid leak resistor is used to bleed off ('leak') excess space charge (the cloud of electrons boiled offa the filament), otherwise the tube would self-bias to cutoff. It also provides detection (demodulation) of the RF signal via the nonlinear characteristic of the response curve.

I've amassed a gaggle of 20's sets over the years; it frustrates me that a device so simple can befuddle me that much! A lot of the issues seem to be open coils, bad connections, bad grid leaks. I've had mixed results but do have a set or two that perform okay.

The signal generator is probably acting as a coupling devise to your homes AC wiring, which is acting as a makeshift long wire antenna. The down side to using your homes wiring is that the radio will hear all kinds electrical noises riding on the power line. Even the ground wire to your homes electrical system may act as an antenna at radio frequencies.

There are two small transformers in the set, does anyone know what they do?

With a television, I can look at a block diagram and schematic and generally figure out what's going on. With this it might as well be magic or something, because with five of the exact same tube I'm not really sure what anything inside this thing is really doing.

Until I get some sort of grasp on how the radio works, it's like knowing how to replace a fuel pump in a car but not knowing if it's even bad, or knowing how a fuel pump makes the car run.

I assume these are some sort of interstage transformer, and since there were so many 5 tube battery sets made there must be some sort of spec to them. I just can't find anything other than crude diagrams that look like Abraham Lincoln drew them on the back of a shovel with a lump of coal......

Usually air core = RF trans, iron core = audio trans. If you know where the antenna and speaker terminals are that helps tell what is what. Most sets with a straight line of tubes have signal flow/stage cascading linearly along that line. If you know which end is audio and which end is RF, and then can figure out which one is the detector then you've pretty much chopped it up into it's 3 types of stages. Usually the detector will have some meg ohm resistor feeding it's grid instead of an just an RF or AF transformer grid winding.

I wish I had time to track down a modern redraw of the Atwater Kent model 40 I used in a resto (it's on the net somewhere)...It gives a good idea of the anatomy of a typical 6 tube TRF receiver. A lot of 20's schematics in addition to being poor scans of riders (that is a topic in and of it's self), are drawn less as a schematic and more as panel wiring diagrams with no real standard...It was the wild west days of schematics and it takes some imagination, patience, multicolor highlighters and sometimes redrawing the thing in a non-bassackwards way to follow them...

Most 40's and later sets I can usually grab an iron and go blind, and if needed read important info off the schematic at a glance, older stuff often has moments of staring at the print and or chassis and tracing things out to make sure I'm not seeing things wrong.

Yes, these are interstage audio coupling transformers. Typical use would be one transformer between the gridleak detector and first audio stage, and another between the first audio stage and the audio output stage. Since the simple triode tubes of the era (01As 199s and the like) had pretty low gain, the transformers "step up" ratio actually was used to boost the signal between each audio stage. A 3:1 ratio was common, but other ratios were used as well.
What are the tubes in your set?

jr

Five 01As. All I'd need to do is see a simple decent schematic of a similar set with values and part identification to start the process of understanding this. Only thing I've run across is poorly drawn pencil schematics with nothing but symbols.

You're 100% right because I have a wonky socket on the bulb on my workbench light....when it cuts out I can hear it on my radio 20 feet away.

Now, that said, I'd have to think there's a simpler way to make such a coupling device to do just that rather than use my signal generator. I tried coiling a wire around an AC cord thinking that might create a capacitive coupling, but no luck. I've searched out references to an .001 cap at a high voltage connected to the AC line somehow that accomplishes this, but can't find any direct references.

There is a fairly decent generic schematic in this wikipedia article. The diagram shows three audio stages rather than two and uses the less efficient resistor capacitor (rather than transformer) coupling between two of the stages. If you eliminate the second audio stage and put a transformer between the detector stage (grid leak) or first audio stage and the audio output stage, it should fairly closely resemble your set.

https://en.m.wikipedia.org/wiki/Tune...uency_receiver

hope this helps,
jr

This might be closer:
http://upload.wikimedia.org/wikipedi...rcuit_1924.png

jr

Would you like to go over it stage by stage?

.

Here's a whole slew of Atwater Kent schematics redrawn to modern standards. Take a look at the model 20.

http://www.atwaterkent.info/TechData...wingIndex.html

For your indoor antenna try connecting the radio's ground to the third wire ground(green) of your homes AC wiring, which in theory goes to earth ground at your service entrance. Then try a short length(10-15 feet of whatever wire) stretched out across the basement floor. That short wire should pick up whatever radio signals are radiating off your homes AC wiring. I have very good reception from local stations using this method, but I also hear every appliance in the house turn on and off, as well as well as all the crappy wall wart switching power supplies that most every modern day electronic devise use. Nothing can compare to a 50-100 foot wire strung up outside far away from other electrical interference. I have about 50 foot going from my shop to a tree with a grounded shield coax(75 ohm) leading all the way to my basement. Ideally you want to earth ground the coax shield only where the antenna enters your home, then you can use the shield as the radio ground at the other end of the coax. Yes there are loses using coax for lead in but they are negligible relative to the overall clean signal you receive.

I'll give that a shot.....

See, the reason for all of this is that I'm going to be working on a Radiola III. Might be some nights when my wife is doing whatever, that I might want to emerge from the basement and sit in the living room and recline on the couch with the radio on a small table and put the headphones on. That's not going to be very easily done if I have to string a huge antenna....and my living room is on the driveway side of the house and the front. Not really conducive to a long antenna, and what if I decide I want to move to the other side of the couch or another room? This is why I want to make it more "portable".

And I'm guessing, why more people don't express an interest in these dinosaurs. If there were an easier route here, I'd be willing to bet that more people would express an interest in operating one.

In that case, adequate is good enough because the station I'd want to listen to is a short distance from me.

I've had some luck hooking up one end of a 40's 'loop' antenna to TRF sets.

First thing I tried....no good.

If you have an attic and a none metallic roof you could run a wire up there. But unfortunately there's no magical way to pick up a strong clear AM signal with a puny little indoor antenna. The real key is in getting the antenna away from unwanted noise sources.

Next time you go on a trip put your car radio on AM and hear how nice it picks up in the country but once you get near groups of homes it goes downhill fast. Thats about the easiest way I can describe AM signals and the frustration for some receiving them.

Some used to hook to bed springs but hardly anyone has those anymore. Perhaps a furnace duct may work? What little indoor antenna work Ive done it seemed like the longer the wire the better. I did build a montrosity of an antenna about 4 feet high with wires thru holes of wood pieces (I forget the term) around and around the wood pieces and that worked pretty good. it wasnt a bad directional TV antenna either.

Late to the party here but ran across this thread searching for TV antenna advice. Just wanted to add that a straight wire in the attic makes a pretty good AM antenna. It's most sensitive in the direction perpendicular to the wire. You do need a good ground too.

I think what fixmeplease is talking about is a 'loop' antenna. I have an old article somewhere for "The AM Super Loop" which was a diamond shaped wood frame this guy hung from the ceiling of his radio room (or attic) on a rotatable mounting so he could point it in any direction.

I'm sure some of the antenna websites have DIY designs and something should fit your situation. Noise is rampant on the AM band these days though. Watch out for fluorescents, dimmers, computers, TV cable equipment, etc. etc. If you get a lot of noise try turning things off that you aren't using.

Look Ma, no wires!! :D

My progress so far:

https://www.youtube.com/watch?v=PnB-...ature=youtu.be

That AK 20 is a fine example to use. I wonder how many years that Capehart had the patent on that loop. It was not until 1939 that most all radios began using loop antennas.

About 10-12 yrs back, I lucked upon a Grebe Synchrophase that was either brand-new, or had never suffered the indignity of being actually "Hooked up". It even smelled new. Would LOVE to check 'er out& see how she performs !

I saw one of those Grebes in a floor cabinet that was like a drop-leaf table with a speaker on the apron. even the grill spelled out Grebe. A well-stocked collector near here has one in his "radio museum" That set also has a place to hide the batteries, right?

Naw, mine's not like that. We're pretty close to Gatlinburg/ Pigeon Forge/ Great smoky mtns national park, lotsa "Aunty-Que"junk shoppes to liberate you from yr money. A couple yrs back, this one had a black metal console radio that looked new.

I have the Terk loop antenna I use on my Radiola 60 and it works great...I forget the term for this outboard antenna. It is just a loop with a variable cap to match the freq. A bit tricky as you have to tune the station and then tune the Terk to that frequency but it works.

CCrain used to sell a ferrite-bar twin-coil antenna. Again, this requires adjusting by frequency. Mine's on loan. If you can find a used one for a good price, buy it! You can't go wrong.

Ratshak made a very nice loop "Tenny" a few yrs back that was plenty good enuf to use as the tenny for my big Yammy receiver. It wasn't as good as my late, lamented Kiwa, but RS was roughly $25, & the Kiwa was about $400, IIRC. As well as I recall, the RatShak didn't embarrass itself, even if I hooked it up to one of my big hollow state Boat Anchors..

My antique radio collection dates back to the 1950s-1960s, by which time most small table radios were using loop antennas, often with an external antenna terminal for use in fringe reception areas. Almost every one of my radios, except the AM tuner in my bookshelf stereo system, has such a loop on the back cover; these antennas work quite well even in my area, 35 miles or so from Cleveland AM stations. They even bring in DX reception at night (after sunset, of course) from the East Coast (500 miles or so from me) and two Great Lakes states (Ohio and Michigan). The furthest I have received so far in this area after dark using a loop antenna has been Dallas, Texas (WBAP-AM), although there was one exceptional case in the 1980s when I picked up KOA-AM radio in Denver after the local AM on that frequency had signed off for technical maintenance. That was the only time I had ever heard in my area any station, AM or FM, from the Rocky Mountains, using an AM radio (the AM tuner in a Zenith stereo system I had at the time) with a built-in antenna.

Getting back to the topic of this thread, I have never heard 1920s-era AM radios (battery-operated or otherwise) in operation, although I did read a post to ARF recently in which someone discussed a 1920s vintage Crosley radio that didn't sound all that great, even after it had been electronically restored. The radio had a good-sized speaker, but the sound was (according to the poster)...how should I say it, passable for sets of that era but definitely not hi-fi. I honestly do not believe this was or could have been entirely the fault of the design of the radio (the sets were built as well as the state of the art allowed at the time), as I am sure most, if not all, '20s-era AM radio stations were not built for high fidelity (narrow frequency response, for one thing). This is likely why many, again if not most (there were likely exceptions, such as Zenith) radios of the '20s sounded tinny and low-fo compared to sets built in the following decade and beyond. Radio itself was in its infancy in the '20s, so it was unrealistic, IMHO, to expect hi-fi sound from any radio, since most used horn speakers, built in that era--the stations themselves were not that great from a sound standpoint.

BTW, I am 60 years old (almost 61), so wasn't around to see, let alone hear (except by means of old broadcasts on tape, such as NBC's "First Fabulous Fifty" retrospective which was broadcast in 1976 over the NBC radio network), any radios or radio broadcasts from the 1920s. My comments above are based on what I have read (and am still reading) about the history of U. S. AM radio (I am very interested in it, especially the history of the former NBC radio network), and on what I remember of my relatives telling me about radio of that era. I still have a CD I made of the entire NBC "First Fabulous Fifty" retrospective, which is still available on the Internet (I don't recall the URL at the moment).

If you live in an apartment building, the small loop AM antennas may pick up your area's local stations but I wouldn't hold out much hope for DX. The reason is the noise level in most such buildings. I live on the first floor of a 2-story building and do get quite a bit of noise from various sources--microwave ovens, switch-mode power supplies such as are used in home computers, and the like, so any AM "DX" I get is ordinarily garden-variety stuff from 50kW stations in nearby states (within about 500 miles)--Pennsylvania, New York City and Chicago. I get my best AM DX, amazingly, during power outages, when the noisemakers (microwaves, SMPS power supplies, etc.) are temporarily silenced, but when the juice comes back on, so does the noise.

Here's a question on crystal sets, as a topic shift. Does the type of diode make a difference re: reception? I stuck a 1N4001 in this crystal homebrew I have (it's the only thing I had on hand at the time), and it works....but seemingly only from about 1100 KC up.

I think the 1N4001 diode has a lower frequency capability than the 1N34 diodes used in most crystal sets. If I remember right, hot cathode detector diodes work fine also.

G'day all, just on diodes for crystal sets, in theory anyway, germanium diodes are best in terms of sensitivity and the lowest forward voltage drop but the whole subject is actually quite complex and involved.

In this country anyway (Australia), true germanium diodes are rapidly being replaced by 'germanium diode equivalent' schottky diodes like the BAT46 which are actually excellent and are measurably better than germanium types in several respects, like very little reverse leakage etc and are also very sensitive. Regards, Felix aka catman.

You really need a germanium diode for a detector, silicon just won't cut it.

I only delved into 1922-26 battery and crystal sets a few years ago and find them very interesting to tinker with. I use an AM transmitter with mine, so that helps a lot. I find the '22-'24 1,2, and 3 tube sets a challenge to get playing just right. Almost every time I go to play them they need readjustments. The biggest problem is low or garbled audio, but after tweaking about every control I'm able to improve it. My two post-1925 5-tube "three-dialer" casket sets play flawlessly with their cone speakers with hardly any readjustments necessary. With the transmitter the crystal sets play perfectly with their galena crystals. The sound is truly "crystal clear"! :)