What strikes me most is how mechanical these old radios were. From the mechanical tuning capacitor, to the tubes, to the volume control. And yes, those wood cases seemed to be meticulously built.
But on the other hand, one reason electronics were this way is because they had no options. If they had plastics, they wouldn't have used wood. If they had solid state electronics, they never would have bothered with these touchy and expensive electro-mechanical tubes. But they are fun to watch as they glow.
Those mechanical tuning capacitors could be problematic. We had an old radio where that tuning capacitor became vulnerable to the slightest vibration, emitting loud thumps, and was scratchy too. Tubes changed characteristics as they aged, or just as they warmed up with each use, were an egregious waste of energy, and were so bulky that the electronic design always had to be compromised to keep the number of tubes required in check. And so forth. These old electronics are fun to look at, but we have also come a long way.
In spite of the common wisdom, solid state electronic products can be far, far, far more long lasting than these old radios or phonographs. I'm still using an amp I built in 1980, for instance. Hard to do that with these old tube jobs. The tubes would need changing, plus the heat they emitted caused other components to fail as well.
Most modern electronics are going to be dead within a decade. Modern electrolytic capacitors are good for a few thousand hours at best. But I have turned on many a 70 year old radios and they play just fine. The 1941 Zenith console here in the living room has its original electrolytics in it, now 72 yrs old and still perking. The older the better, actually-- that Radiola has paper capacitors, which might be slightly leaky, but still work just fine 88 years since they left the factory. The audio transformers sometimes go open, as they have like 50 Henrys, bazillions of turns of #42 wire in them, which is prone to corrode and fail.
Holy smokes, it was simple. You have three consecutive transformer-coupled RF amps, each one tuned in synchronism with the other two by virtue of the mechanically ganged tuning capacitor. Then the envelope detector, nothing more than a low pass filter. Then two series connected audio amp stages. All transformer coupled, class A, no feedback, no separate voltage and current amp stage in the audio amp.
The first audio output has a high-pass filter, to cut down the squealing no doubt. They didn't like anything above 5 KHz audio in those days. And the really odd thing is the volume control. It operates on the voltage appplied to the *heaters* of the RF amps. How weird is that? As opposed to being a voltage divider just before the audio amp. I wonder if that was prevalent back then?
I have seen the volume filament control on other early radios. It worked nicely on strong local stations; you could burn just enough battery power to get a decent sound to your headphones or perhaps an early loudspeaker. And with the lower gain, meant later stages were not overloaed from a strong signal. However if you were trying to pull in a far away station, and getting the most gain out of the tubes, you would shorten your battery life.
@Bert22306 : And the really odd thing is the volume control. It operates on the voltage appplied to the *heaters* of the RF amps. How weird is that?.
My Dad was an army radio operator on the North West Frontier of India, way before WWII.
I seem to remember he told me that a lot of houses of this era did not have an electricity supply. So the sets were powered by a 2 Volt wet lead acid accumulator, a dry cell grid bias battery tapped at 4.5 volts to 9 volts and a dry cell HT battery with tappings at 120 v Dc to about 200 V DC. The grid bias battery and the HT battery lasted a fair time, but the big drain was on the heater battery.
As you had to lug the battery down to a charging point, which in England was usually a bicycle and radio repair shop and pay for it to be recharged. it made great sense to reduce the current taken by the heaters and thus put off recharging the battery for a bit longer.
If anyone can confirm this, it means I did learn something about valves from my Dad, even though I quickly moved to the germanium transistor, as soon as it became available on the DIY market.
I can confirm the comment about lugging batteries around; my father worked for the original Curry's store in the UK before the war, and aside from folks bringing in batteries for recharging, he used to have to collect and deliver them on his bicycle (Old Man Curry was too cheap to have a delivery van).
Another story from that era was the gas-powered radio - I didn't believe it until I saw the repair manual - literally a gas burner heating up a bank of thermocouples! Thats what you call letting the set warm up..
Thanks, Herr Bell, for posting that schematic. This stuff animates me on so many levels: I'm an EE, I'm a guitar player who plays the kind of music that requires massively heavy tube amps (both uses of 'heavy' apply), and finally I've studied many an audio amplifier schematic in my day and I love to apply my EE skills to tinkering with my amps.
In doing so I've gained a lot of respect the classic tube designers of the early part of the last century. They were true engineers who did so much with so little. Just look at that schematic. It's clean, it's efficient, it is indeed a thing of beauty. To me it is down right artistic. (And on a technical note, one thing that jumped out at me is the use of filamentary tubes - where the filiment and the cathode are one. Being from 1927 these tubes pre-date the subsequently developed indirectly-heated tubes seen since the 30s, and which are the building blocks of all guiatar amp designs. This makes sense since most of those designs are basically lifted from a standard audio amp design of the 40s, brought to you by Mullard, through Leo Fender).
But that was my second impression. The first thing that jumped out at me is the price: $82.50?! In 1927? Are you kidding me?! That had to be on par with most mortgage payments back then, likely more. They couldn't have sold many of these things.
Anyway, these days tubes survive in only three markets: guitar amps, high-end audio and some high voltage radio transmission applications. Little money can be made there, but I love this classic stuff. Studying it has a redeeming quality for EEs today as well. It helps to know where we all came from. I recommend everyone do it. Please keep it coming and thanks again.
Caleb, I was recently given an old set of Audel books, copyrighted 1917 to 1923. They include some sections on electronics and radio, and a great deal on electrical power in general, both large and small. It is indeed interesting to observe how things were done back when labor was cheaper than materials. The effort required to add an outlet to a room in a house was a whole lot more than it is today. And a lot of the explanations for how electrical things work are interesting inn that they assume no previous exposeure to electrical anything. Really a fun read book set .
Very nice, Caleb! I presume you have not fired it up? It's so simple it shouldn't take much to get it going, you should be able to build a power supply to supply all those voltages. You could use a battery powered amp for the speaker if you can't find a suitable speaker or headphones. Or I daresay you could make do with a mains-6v transformer and put a small 8R speaker on the 6V side - frequency response wouldn't be great but hey, it's only AM. Of course if any of the tubes don't work you'd probably have a problem finding replacements....
Elektor Magazine has a monthy column "Retronics" where they do similar "teardowns" of old electronics - mainly test equipment. It's one of my favourite parts of the magazine.
I cut my teeth on valve radios (thought not this old) and remember them with great affection - especially things like Magic Eye tuning indicators...
Sorry Mr C but IMHO that thing is an ugly piece of junk! Only its mother would love it!
Now don't get me wrong, it fascinating to have such a great teardown, and thanks to the other commenters for the schematic and great circuit analysis (leaky grids and control of volume by heater current indeed!)
But I have to say that such a monstrosity would have no place in my home, maybe it could be converted into a graden bird house if the birds aren't so concerned about their street cred living in such a hovel.
I remember doing a restoration on a similar beast: the best thing about the job was the smell of ancient flux when you finally get the old solder to melt. It smelt like cracking open a pharaoh's tomb :-)
Speaking of Zenith Transoceanic, my dad got one too, in 1966. Did you look at the schematic? It had a really basic AM section, which includes the SW bands of course, and it had a single IF of 455 KHz for all AM bands. Not the best way to keep intermodulation products under control.
Not only that, but in 1966, schematics were still drawn as if they were for tube circuits. So just as tubes are usually shown on top, so were the transisators of the 1966 Zenith Transoceanic.
I guess I'm saying that the Zenith Transoceanic sort of followed the same simplicity of design paradigm as this Radiola, although of course from the superhet era.
Then we got a Grundig multiband radio with dual-converion IF ...
@Caleb - it looked like steel or metal of some sort was used for the dial cord - if so and if you can free that capacitor (WD40?) it should not take much more to get it going. Otherwise you'll have a job renewing the dial cord - I used to do a lot of them when I was younger and some of them can be real sods to get right.
@David : As a watch and clock repairer I never use WD40 on bearing surfaces it dries out and increases friction. Better to use Three in One oil, it gets in to joints frees and polishes. Mind you friction on that variable capacitor would not cause a lot of problem. Like you, I found some of the dial cords could be a big pain to replace
Not much other than a name. rca.com doesn't even have contact info, much like another name that exists only in a name: Westinghouse. I'm convinced that the names are owned by Chinese companies who use the name for the name's sake.
Case in point: my father-in-law has decided to replace his tube TV with a flat screen. He immediately gravatated to RCE because to him, RCE is symonymous with quality. I told him not to bother, it's just name now, bought by a company because there are people do relate to the RCA name.
Thanks for sharing your Radiola 16. I have a house full of old radios, it's an affliction that I've had for several years. There is no known cure.
A lot of the metal used in these old sets was "pot metal" which is known to "grow" or creep. Tuning condensers and pulleys, etc. are negatively affected by that. The tube in image 13 appears to be equipped with an "anti microphonic" device. Audio output tubes were famous for microphonics and there were various cushions, sockets, and rubber covers available to cut down on howling tubes.
Best wishes with your radio. It's very important to remember where we've been.
Since household radios of that era tended to be large and bulky, this looks like a first attempt at miniaturization. And what a fine example it is. It's unbelievably small by the standards of the time and the internals are well protected by the wooden box.
The electrical design also appears to be well thought out. From the three-section tuning capacitor, it appears to have a tuned RF amplifier on the front end. Generally one section was for the Local Oscillator, one for the Mixer and the one for the Antenna input. Later radios eliminated the RF amplifier resulting in less sensitivity and selectivity.
I didn't see a speaker so this was probably designed to be used with headphone, fairly common during those days. I have to wonder if they offered an optional amplifier and speaker like the i-phone does these days. The more things change...
When I was a pre-teen, I would inherit radios similar to this one from neighbors that were upgrading to house-powered units. Batteries were always the issue. They were expensive and didn't last very long. I soon figured out how to make my own power supplies that could run off the mains.
It's interesting to analyze the design to see how the engineers of the day were able to use their imagination to overcome lack of materials, components, and technology and end up with a pretty capable performer.
If someone had the inclination to trace it out, I would really like to see the schematic.
Generally one section was for the Local Oscillator, one for the Mixer and the one for the Antenna input.
Superheterodyning came along later, no local oscillator in this beast. There are three stages of tuned RF amplification. The ganged cap was an improvement over earlier models that required each section to be tuned seperately. That kind of made you stick with one station, as it was slow and difficult to change stations.
@BobsView, 11/15/2013 - "TRF Forget about that one":
I'd say that's pretty accurate statement ... Looking the orthogonal arrangement of the tuning coils, the designers were doing their best to reduce coupling across the stages. I can only imagine tuning across the dial, headphones on and coming across a strong station while having the volume up to pull in a far away station.
I liked the linear arrangment of the tuning dial. The designers went to some extra effort to design and build a nonlinear capacitor.
About 50 years ago, an old friend asked me about getting his old radios going. They were obviously the Rolls Royces of their day. Huge multi-ganged capacitors, 12" electromagnetic speakers. The speaker's magnetizaton winding was used as a choke in the power supply. There were separate chassis for the power supply and audio amplifier. All very impressive. One actually worked with a very unpleasant sound from the disintegrated paper cone. Moving any of the wiring resulted in bare conductors, the insulation was so brittle. In those days before the Internet I couldn't find replacement tubes or speakers. So I politely passed on the request to repair the beauties. I believe they were trashed.
Today, all of my over 50 year old Heathkit tube equipment still works, when called upon a couple of times a year! My EICO tube stuff has all packed it in decades ago (transformers). You can still get all the tubes and most components you may need off the Internet today, though I've never had the need.
My 1969 vintage Quad electrostatic speakers and solid state preamp and amp are still in daily use, still supplying the best sound I've heard for 42 years. I cannot believe how poor the quality is of current production speakers in comparison. If need be, the discrete components used in this equipment are still readily available. My only addition to our audio system was a Sony 15" sub-woofer that I got for $200 on clearance 5 years ago.
Any recent electronics with its custom ICs becomes unserviceable in very few years. Many is the time I've requested a part from a reputable manufacturer only to be told that service parts are no longer available after only 5 years.
I certainly have no room in our house for all the pieces of unrepairable electronics I've been offered. The real thrill is having an antique that works like new.
It is indeed a Tuned Radio Frequency design. One quite interesting point, the intemnediate stage transformers are aligned on different axis' - this was done so that the stages would not couple with each other - the magnetic fields from the coils point in different directions. If they did couple, then the stage would oscillate. It is a lovely piece of engineering - thanks for sharing it with us.
That radio looks to be in good shape. It should take very little to get it working, since it doesn't seem to have any electrolytic caps. A little solvent to thin the grease on the tuning worm, and some cleanup to break the corrosion that has frozen the tuning cap in place. May have similar problems on the pots. That exposed wirewound will certinaly be noisy, but a little pot cleaner will do wonders for it. Won't hurt to use it on the tube pins also, since ancient corrosion will have built up.
That would have been a battery powered headphone unit. These days you would want to build a well-filtered power supply for it, 300V batteries are hard to come by and expensive! (Yes, it would have been a stack of 45V batteries or so, but still very expensive today, and wouldn't last all that long.) Beware the filament voltage - it was probably 2V nominal (I havne't looked up the tubes to be sure) and would quite possibly be runing low if supplied by a dry cell, which was common in the early days. There was often a series pot to adjust to the most effective filament voltage. This was often less than the nominal tube voltage.
You would probably have to run out 20-30 feet of wire for an antenna on this thing, especially if you live in a highrise building made of steel. A good ground might also help reception considerably. If you have nearby stations you could probably pick them up fine just using a 3 foot cliplead on the antenna terminal.
Freeing up the tuning cap: you may be able to get it lose with a little NON-silicone pot cleaner. Spray some on the grease and bearing points on the tuning knob, and some at each of the bearing points on the main condenser shaft. Rocking things back and forth might start to break things lose. You might end up having to use somethinng like some Kroil to get things broken lose. Then you need to rinse it out with some thinner or other thinn solvent, and re-lube wth some decent lube. Be careful with lube on the condenser bearings, the shaft and pltes are grounded through those contact points. A little lube is good for preventing corrosion and smoothing operation, but too much can cause grounding problems.
NASA's Orion Flight Software Production Systems Manager Darrel G. Raines joins Planet Analog Editor Steve Taranovich and Embedded.com Editor Max Maxfield to talk about embedded flight software used in Orion Spacecraft, part of NASA's Mars mission. Live radio show and live chat. Get your questions ready.
Brought to you by