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For shop heat ....Happiness is a warm Radio


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This 1949 Marconi AM/FM/SW radio uses 14 vacuum tubes to do what a 5 volt postage stamp can do today. But there's a joy in bringing old hand-wired technology back from the dead. And you don't need to put your work under a microscope to do it.

This super sized table radio was dead when I first tried it, so it was put away, and I went in search of schematics, capacitors (JustRadios in Ontario, thanks Dave Cantelon, for both) and time, which I now seem to have for the first time in years.

I found a cold solder joint in the power supply, where the filter can has been replaced. And just like that, the heaters are glowing and there's snap and crackle coming from the speaker. Joy. This means both that big power transformer and the smaller output transformer are healthy, and I can be pretty sure this beauty will perform again. New capacitors will get voltage levels back up to where they should be. Speaking of voltage, each leg of the power transformer is putting out 340 vdc. That voltage rests on the plates of the output tubes. When a small signal voltage opens the valves, 340 volts drives the speaker cone thru an output transformer. Undistorted output is 5 watts, max output 10 watts. Serial #293. FM was not big in '49, having been invented for WWII.

So 14 hot tubes to heat the shop while I work on the cabinet. I find most old radios have decent tubes. They're not like light bulbs, as a rule. Bad capacitors, bad connections and burnt resistors are common problems.

The plan this winter is to try plastic casting replacement knobs for this and some of my other relics.

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Occasionally, after I get up from my computer, my wife will say something along the lines of "did you and your weird friends have a nice little chat this morning"?

I should be offended, but I never am because ,well, this isn't your typical cross section of North America.

Cool hobby, John. I see the appeal of fixing stuff that's been hand built.

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There is a location in Lockhart, TX (near Austin) that deals with antique radios. My brother (retired Navy now living in Georgetown, TX) had his old radio (electronics and wood case) restored by Neon many years ago.

He may be slowing down a tad as he relocated a year or so ago to a different structure, but could be worth a source for parts.

Neon Radio

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Brings back memories. Must be a challenge just to find parts.

Marc

Yes, the visible parts like the knobs are impossible to find for a rare radio like this one. So I will try to make a couple.

Electronics can be substituted and there are collectors everywhere with boxes full of parts. The only tubes that are in short supply are the big beam power tubes that get burned up by guitar players. We can get those from Russian and Chinese suppliers. The transformers had me worried, because they're expensive and heavy to ship. I would have dug one out of my box and substituted it somehow.

The small table radios don't use a power transformer, just line voltage, and they are everywhere. I brought one home on Tuesday, "$10, Does not work". Well, it works fine now that it's free of a horse blanket of dust and dirt.

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It needs some body work, but there's room on the shelf for it. It's a 1951 Stromberg Carlson Dynatomic with a selenium rectifier and a full complement of original tubes.

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That's gorgeous.

Is it Bakelite?

Yes, it appears to be.

Although it is a 1951, when new plastics were coming in, the cabinet may have been made years earlier.

This cabinet model ran for 5 or 6 years and went from 6 octal tubes in 1946 to this later one, which has the newer mini tubes and a rectifier made from a stack of selenium wafers. Another poison, but nobody worried about that in the 50"s. The chassis has 120 volts on it and nobody worried about that, either.

How many watts at the wall plug?

I'm not sure how to answer that. The Stromberg transformerless radio runs on line voltage and has a max output of 3 Watts.

That is because the power tube used (big one on the end) is a 50L6 which can put out 3 Watts with a plate voltage of 130 VDC. The rectifier alters AC to DC.

You can get more Watts by using more powerful output tubes and more advanced designs.

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What's poisonous about selenium rectifiers?

Marc

If you eat a selenium wafer, you will die. It is toxic in large doses. There was a TV murder mystery in the early 90's in which the late John Ritter poisons his wife by scraping selenium from his old radio and serving it to her in her tea. That is how I know. I saw it on TV.

I'm not sure how to answer that.

Sorry, unclear question. If you plugged the radio into a Kill-A-Watt meter, how many watts would it show to be using? I know there are only a few watts of sound, probably a lot more in heat.

OK. 0.28 amps at 110 volts for the small radio. It consumes about 33 watts. Not enough light to read by.

The big Marconi FM radio draws 1.06 amps at 110 volts, maybe 120 watts needed to operate it.

Yes, most of the power consumed is used to heat the elements of the tubes. They need to be hot to work. Edison discovered the diode while he was working on building a better light bulb. When he added a grid, the triode, which is an amplifier, was born.

Transistors amplify current, not voltage. That is why we can run a transistor radio on a flashlight battery. Also, no heat is needed to make transistors work, so no heat for my shop there. [:(]

Tube powered TV's were the ultimate energy hogs. All that heat would cook the components, so resistors and capacitors would drift out of spec. People would pull tubes, the only user friendly parts, and run to the corner store to try and figure out why Hoss's head was bigger than his hat. [:)]

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Transistors amplify current, not voltage. That is why we can run a transistor radio on a flashlight battery. Also, no heat is needed to make transistors work, so no heat for my shop there. [:(]

BJT transistors and vacuum tubes both exercise control over current. The voltage is supplied by power supplies and is at different levels for different technologies.

The 'amplified voltage' said to be produced by them is actually developed by resistive loads installed between the power supply and the vacuum tube plate or BJT collector.

'Course you already know that.

Marc

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Transistors amplify current, not voltage. That is why we can run a transistor radio on a flashlight battery. Also, no heat is needed to make transistors work, so no heat for my shop there. [:(]

BJT transistors and vacuum tubes both exercise control over current. The voltage is supplied by power supplies and is at different levels for different technologies.

The 'amplified voltage' said to be produced by them is actually developed by resistive loads installed between the power supply and the vacuum tube plate or BJT collector.

'Course you already know that.

Marc

Thanks, Marc. I should have said something like "transistors don't need high voltage to do their thing" and quit there. Of course, we don't even see transistors anymore. They're all integrated into those mystery chips with 20 or 30 legs.
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That reminds me of when I was runt in the mid-1960's listening to SW on old sets like that.. "C-H-U Canada" would give the time with a bong.. they'd announce it in French (Oops..Quebecois?) and English.. ".. Dix heures, cinq minutes..". BBC was cool to hear with that sound phasing in and out...

That 'phase shifting' sound was cool to hear... (Jimi Hendrix's engineer Eddie Kramer used it in the studio by pressing on the flanges of the tape-reels apparently.. . Now we call the device that guitarists use to do it a 'flanger'). I digress..

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That reminds me of when I was runt in the mid-1960's listening to SW on old sets like that.. "C-H-U Canada" would give the time with a bong.. they'd announce it in French (Oops..Quebecois?) and English.. ".. Dix heures, cinq minutes..". BBC was cool to hear with that sound phasing in and out...

That 'phase shifting' sound was cool to hear... (Jimi Hendrix's engineer Eddie Kramer used it in the studio by pressing on the flanges of the tape-reels apparently.. . Now we call the device that guitarists use to do it a 'flanger'). I digress..

It sounds like (pun) you were listening to a regional version of the CBC. The CBC is our national radio station, funded by tax money, and is broadcasted across the country from a bunch of locations.

When I plug in this whole wall of radios, I can get about 450 Watts of heat from it. [:-thumbu]

But the 60 cycle hum makes my teeth rattle and a filling in my mouth tries to sell me a car. [:)]

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Very nice collection...........I especially like the chandelier[;)]

Greg

It's a trouble light, and it's no trouble at all. [:)] I like flexible lighting, so I have a double duplex receptacle box near the ceiling on a switch.

Since it is a little slow right now, here's some more pics of my old junk.

A Stromberg Carlson mono radio/turntable unit circa 1950, before and after.

I bought this for parts. Did someone actually design this thing?

Then my daughter started bringing old albums home to play on it. So it became a keeper of sorts, storage for her stuff, that is.

Since I felt obliged to keep it, can't sell it, can't throw it away, I decided to modify it a bit.

It is now the guitar player's computer desk, and it can still play LP's if it has to. I put the turntable drawer in the back above the amp.

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  • 2 weeks later...

John,

You can probably identify the model of this Zenith floor radio right away. It was at today's house. I like the art deco knick-knack on top too.

Too bad there's nothing worthwhile to listen to on AM radio. I have my receiver hooked up to the internet and found a few FM stations to put on my favorites list. I listen to a jazz station from France (all English tunes), a classical station from the Netherlands, and a blues station from England.

Anyone else out there trying HD music? I bought a music server from Olive and have downloaded some HD music from HDTracks. The quality of the music is incredible, I just wish my ears were in better shape.

Olive Music

HDTracks

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  • 3 weeks later...

That's some neat old junk. The Zeniths were always topnotch equipment.

I can't hear stereo so hifi is wasted on me. I'm a lo-fi guy.

The big Marconi brings in a couple of good FM stations and I can plug a Sanyo Discman (remember them?) into the phono jack if I get sick of commercials. I replaced 26 capacitors and a few resistors. The tubes are fine.

The way to enjoy the old AM radios is to broadcast your own music with a little low power transmitter. Then you can tune your radios to that frequency. Fun. My transmitter is an old Heathkit Signal Generator with a wire on the output. You need to pick a quite spot on the dial, that's the hard part sometimes.

Joe, you don't want to plug that one-track cassette machine in unless you're wearing your insulated rubber boots. Metal cabinet, two-prong cord. It will try to bite you. [:)]

Marc, I found the site where you can learn all about poisoning your spouse with a radio.

http://antiqueradio.org/tvshow.htm

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