Dynamotor

Another treasure from my brother's attic.

I think it dates back to WW2 - it still works!

My Dad used to take it on camping trips so he could use his electric shaver! I was expecting to get AC out rather than DC, so I'm kind of surprised his shaver worked. Anyone explain that?

http://www.youtube.com/watch?v=rs8_appzFg0

Ah, memories: my father had a dynamotor in the trunk of his car to generate the B+ for for the transmitter in his ham rig. The receiver was one of those new-fangled solid-state jobbies, so the dynamotor only came on when he was transmitting, and he had to learn to wait for it to spin up after keying the mike.

The shaver works on DC because it's a "universal" motor (scroll down a little to read about them). Those are very common in small tools and appliances.

Yes I recall using one in the early 60s to power a small 2 meter transceiver in my car, a Heathkit 'two-er' for those that remember. The filaments of the tubes would use the car's 12vdc and the dynamotor would provide the +150vdc for the tube plates. It worked but lots of humming noise that would track with the rpms for the car's motor. Dynamotors had terrible efficiency values but would work in a pinch.

Lefty

Interesting topic. Apparently I'm too young to participate. I did leach/stand by and listen in some knowledge of powering tubes on a car though so thanks. I found the tube technology of the past century fascinating. I've just used tubes to explain diodes and transistors to my students. I think it's much easier to understand compared to majority or minority charge carriers what not in semiconductors.

So if you run your tubes at a couple hundred volts, do you need metal shields against soft x-ray coming out of the tubes? I've seen those shields in my teaching prep place. Do those tubes make humming noise when lit?

Awesome! Ancient tech is so beautiful compared to todays micro-electronics. I love to watch that stuff in old museums.

So if you run your tubes at a couple hundred volts, do you need metal shields against soft x-ray coming out of the tubes?

No, those slip on metal shields were actually used to help keep the tubes cooler then without them, as it forced the rising heated air to exit the top while cooler air entered the bottom of the shield. Very high voltage TV horzontal sweep section in color TVs could sometimes generate X-rays so extra metal sheilding was used around that section of the TV.

I've seen those shields in my teaching prep place. Do those tubes make humming noise when lit?

Filaments of tubes (used to boil free electrons off the cathode element) were often powered by 6 or 12 vac power and the plate (and screen) high voltage DC supply both could cause some 60 or 120Hz hum, but general good design and layout would keep that to a minimum. Early Hi-Fi amps were all tube tech and didn't suffer any hum in well made equipment.

Lefty

liudr: Interesting topic. Apparently I'm too young to participate. I did leach/stand by and listen in some knowledge of powering tubes on a car though so thanks. I found the tube technology of the past century fascinating. I've just used tubes to explain diodes and transistors to my students. I think it's much easier to understand compared to majority or minority charge carriers what not in semiconductors.

So if you run your tubes at a couple hundred volts, do you need metal shields against soft x-ray coming out of the tubes? I've seen those shields in my teaching prep place. Do those tubes make humming noise when lit?

liudr - if you're really interested in this stuff, check out old back-issues of Popular Science and Popular Mechanics on Google Books (anything pre-1970s - PopSci goes back to somewhere around 1875 or so, from what I could gather). Lots of interesting stuff about tube-based electronics, especially during the 1950s (where it really has gotten interesting - I've been reading all the issues from January 1950 onward - has been from about 1957-58 or so, when transistors started to come down in price and got incorporated into ordinary stuff - this is also the time when PCBs started to gain real traction, mainly in televisions - so you start to see weird stuff with transistors -and- tubes in the same circuits!).

BTW - there was such a tube-era device called a "vibrator", where it was used in early automotive radios to boost the car battery voltage up higher, just like this dynamotor. It was basically a small self-contained induction coil device of some sort (I have yet to find a good description of how it worked exactly, but I have a good idea - likely something like a Model-T spark coil system, but much smaller, and likely using an oscillating coil, instead of points). Apparently it made a humming noise when in operation...

BTW - there was such a tube-era device called a "vibrator", where it was used in early automotive radios to boost the car battery voltage up higher, just like this dynamotor. It was basically a small self-contained induction coil device of some sort (I have yet to find a good description of how it worked exactly, but I have a good idea - likely something like a Model-T spark coil system, but much smaller, and likely using an oscillating coil, instead of points). Apparently it made a humming noise when in operation...

Not quite that amazing. ;)

A vibrator was just a 12vdc operated 'vibrating' relay with SPDT output contacts. Think of it as a mechanical 555 chip driving a relay at a fixed frequency, 1-2khz I think, but I might misremember the frequency. The contacts were used to switch the cars +12dc between opposite phases of the primary winding of the radio's power transformer. The secondary windings of the transformer was used to develop the various DC voltage required by the radio. So the vibrators purpose was to generate a chopped +12vdc suitable to for passing through a power transformer. Not unlike a more modern power inverter used today. A very simple and useful device for the tube radios of the day, however because it was electromechanical in nature and the contacts were passing significant current it was probably the most frequently replaced component of the radio. Tubes of course could go bad, but in those days people didn't hold on to cars for as many years as they do today generally.

Lefty

retrolefty:

BTW - there was such a tube-era device called a "vibrator", where it was used in early automotive radios to boost the car battery voltage up higher, just like this dynamotor. It was basically a small self-contained induction coil device of some sort (I have yet to find a good description of how it worked exactly, but I have a good idea - likely something like a Model-T spark coil system, but much smaller, and likely using an oscillating coil, instead of points). Apparently it made a humming noise when in operation...

Not quite that amazing. ;)

A vibrator was just a 12vdc operated 'vibrating' relay with SPDT output contacts. Think of it as a mechanical 555 chip driving a relay at a fixed frequency, 1-2khz I think, but I might misremember the frequency. The contacts were used to switch the cars +12dc between opposite phases of the primary winding of the radio's power transformer. The secondary windings of the transformer was used to develop the various DC voltage required by the radio. So the vibrators purpose was to generate a chopped +12vdc suitable to for passing through a power transformer. Not unlike a more modern power inverter used today. A very simple and useful device for the tube radios of the day, however because it was electromechanical in nature and the contacts were passing significant current it was probably the most frequently replaced component of the radio. Tubes of course could go bad, but in those days people didn't hold on to cars for as many years as they do today generally.

Lefty

Hmm - too bad; sounds like it was closer to the Model T spark-coil than I thought; how much of a racket did they make (I remember making a similar buzzer as a kid with the relay on my 150-in-1 kit, and it sounded like an angry hornet)?

I'm really surprised that they didn't use some kind of resonant vibrator (or something with little or no mechanical contacts), or make a purely electronic oscillator design (maybe as an all-in-one tube); probably just another instance of cost vs profit (with the consumer losing out in the end - it seemed like any mention in PopSci of the device had to do with replacing it).

:)

Universal motor

Thanks Ran. Mystery explained.

Next thing to try out of my brothers loft is a rather lovely bakelite radio. One of the tubes looks black inside - does this mean its likely to be dead?

Hmm - too bad; sounds like it was closer to the Model T spark-coil than I thought; how much of a racket did they make (I remember making a similar buzzer as a kid with the relay on my 150-in-1 kit, and it sounded like an angry hornet)?

Well if you had young ears and the motor was turned off and little traffic noise you could just hear it a little. Pretty quite actually as the dash panels and radio chassis of the day were massive heavy objects that mask out the vibrator's noise.

I'm really surprised that they didn't use some kind of resonant vibrator (or something with little or no mechanical contacts), or make a purely electronic oscillator design (maybe as an all-in-one tube); probably just another instance of cost vs profit (with the consumer losing out in the end - it seemed like any mention in PopSci of the device had to do with replacing it).

Actually in later years they made a solid state plug-in replacement model that would make no noise, it just used a pair of power transistors for the switching output and had an internal electronic oscillator to generate the proper switching frequency. These were used well into the 70s at least as police two radios still used vaccum tubes for the high power RF output stages so still required high voltage DC, so the solid-state vibrator / power transformer lived on until VHF RF transistors got cheap and relaible enough to totaly replace tubes in public service mobile radios.

Lefty

One of the tubes looks black inside - does this mean its likely to be dead?

Yeah, but not necessarily: it might be the “getter”, a coating put on the inside of tubes to absorb the last vestige of oxygen because the manufacturing process didn’t produce an absolutely perfect vacuum.

However, my recollection (possibly flawed, because it’s been about 40 years since I did anything with tubes) is that the coatings I saw usually looked more silvery. So the black is probably a deposit of the magic smoke, but you could be lucky.

Si:

Universal motor

Thanks Ran. Mystery explained.

Next thing to try out of my brothers loft is a rather lovely bakelite radio. One of the tubes looks black inside - does this mean its likely to be dead?

Whatever you do, don't just "plug it into the wall", even if it looks perfect and clean on the inside of the case; there's a good chance that any electrolytic caps have dried out - you plug it in, and you might get fire, instead of sound (this is a bigger issue if the caps are on the power-supply side of things). It is possible to "reform" such caps using a variable transformer (you basically start with a very low voltage, and work it up to full line voltage over a long period), but such is a hit-or-miss technique from what I understand. Your best bet might be to look around on the internet and in real life to find out information on the radio, and if there is anybody who knows how to restore such (in the meantime, see if it has any value on the antique/collectibles market - also, going to such fairs/markets can land you leads to people who know how to do such old electronic restoration; you might also take the time to compile a list of the tubes/valves used, and see if you can find suitable replacements for them).

[quote author=Ran Talbott link=topic=57529.msg414397#msg414397 date=1302029454]

One of the tubes looks black inside - does this mean its likely to be dead?

Yeah, but not necessarily: it might be the "getter", a coating put on the inside of tubes to absorb the last vestige of oxygen because the manufacturing process didn't produce an absolutely perfect vacuum.

However, my recollection (possibly flawed, because it's been about 40 years since I did anything with tubes) is that the coatings I saw usually looked more silvery. So the black is probably a deposit of the magic smoke, but you could be lucky.

[/quote]

I'm pretty sure you're right, Ran; getter coating are more "silvery" (I liken them more to the color of lead, though). Then again, I only base this on what I have seen myself, and what I have read - I know little to nothing more about tube electronics. I myself have an old Zenith tube radio that needs work; one of these days I intend to make a list of the tube numbers and see what I can dig up at Apache Reclamation and elsewhere (I broke my own rule I posted above before I found you shouldn't do it - I plugged it in - no fire or smoke, though - just 60 Hz hum thru the speaker; at least the amplifier portion is likely good, but the RF seems shot in some manner).

BTW - have you looked up tube testers on Ebay lately? At one time you couldn't give them away; nowadays they're fetching amazing prices - I was trying to find a good one a couple of weeks ago, and couldn't believe what I was seeing, price-wise. Must be all the guitar and audio tube-amplifier fanatics out there...

:)

Thanks chaps.

The insides are covered in dust, so I planned to carefully remove each tube and clean it up, as well as all the passive components, and then turn it on and see what happens.

If it doesn't work, presumably the tubes are the most likely point of failure, so I need to find part numbers and then see if I can get replacements.

The only advice I have about tubes came from my electronics professor at college who advised always working with one hand behind you back.

BTW - have you looked up tube testers on Ebay lately? At one time you couldn't give them away; nowadays they're fetching amazing prices - I was trying to find a good one a couple of weeks ago, and couldn't believe what I was seeing, price-wise. Must be all the guitar and audio tube-amplifier fanatics out there...

The responsibility for those high prices on tube testers predominatly comes from two special interest groups. High end 'golden ear' audiophiles that feel the tube based hi-fi sounds better then solid-state equipment. The second ground is the guitar tube amp crowd that use tube amps for the 'proper' distortion sound that such tube amps produce.

Both groups seem to have high disposable income and have done crazy things to the new old stock tube prices and other tube amp components and test equipment. Lots of specialty vendors cater to that market.

Lefty

retrolefty:

BTW - have you looked up tube testers on Ebay lately? At one time you couldn't give them away; nowadays they're fetching amazing prices - I was trying to find a good one a couple of weeks ago, and couldn't believe what I was seeing, price-wise. Must be all the guitar and audio tube-amplifier fanatics out there...

The responsibility for those high prices on tube testers predominatly comes from two special interest groups. High end 'golden ear' audiophiles that feel the tube based hi-fi sounds better then solid-state equipment. The second ground is the guitar tube amp crowd that use tube amps for the 'proper' distortion sound that such tube amps produce.

Both groups seem to have high disposable income and have done crazy things to the new old stock tube prices and other tube amp components and test equipment. Lots of specialty vendors cater to that market.

Lefty

"Wonderful". I collect old computer processors not to use them or pretend they are better than the newer ones. But on the same used cpu market, there are gold extractors that want every last old cpu to extract gold. They're destroying environment and jacking up the price for us collectors and not to mention people selling information on how to extract gold from cpu making cpus look more valuable than they are. So same thing, you want it, you can't get it unless you pay unreasonable price, old tubes or old cpus. $)