1960s Open Reel tape recorders

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Re: 1960s Open Reel tape recorders

Postby McGee2021 » Sun May 21, 2017 3:23 am

Klaas Robers wrote:But do you know the correct English word for such an auto transformer?


Here in America we just call them travel converters, but it is an umbrella term.
John Logie Baird was obviously the man who sowed the seeds but did not reap the harvest.
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Sun May 21, 2017 12:56 pm

I'm not sure where the term auto-transformer came from, perhaps because they have only the single winding? But voltage converter works equally well. These, as we know are not isolation transformers where there the primary and secondary are isolated and usually of the same voltage, but they don't have to be.

I worked at a radio station (commercial AM/FM) many years ago and we had a 5kVA isolation transformer for the technical power (as opposed to the domestic power). 240V in and 120-0-120 out. The centre-tap became the neutral and two 'lives' 180 degrees out of phase. The domestic power outlets were the usual BS1363A type but the technical outlets were slightly different.

At first glance they looked the same as the usual UK plug/socket, then you niotce the neutral pin had been rotated 45 degrees. So you couldn't plug something electrically 'dirty', say a power-drill, into the technical power. When you opened up the plug both the live and neutral pins were fused. I never saw them before or since that radio station.

Steve A.

Just done a quick bit of Googling and here's a similar idea, I can't recall if the usual live pin was round or the standard shape at the radio station...there are surprisingly quite a few variations...
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Sun May 21, 2017 5:19 pm

Some years ago I was wandering around the electonics souk area of Bangkok and in a box I noticed a bunch of transformers. One side said 220V with two leads, the other said 380V also with two leads. Good size somewhere around 80VA, using them backwards (I presumed) I should get a good 500V DC. Two, 1kV, ideal for CRT work. But when I got them home they turned out to be auto-transformers, one wire each side was common - useless. I still have them though.

Can't think of an original use for them except perhaps industrial electrical three-phase control panels to illuminate standard 220V bulbs/indicators or relays/contactors...who knows?

Steve A.

Anyway, must get back to this tape machine...
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Re: 1960s Open Reel tape recorders

Postby Klaas Robers » Sun May 21, 2017 7:07 pm

Auto = Self. So the primary it self is also the secundary. Has nothing to do with a car, an auto mobile. However the auto mobile is a mobile that runs on its own, without horses. Autonomous. A novelty.
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Sun May 21, 2017 7:30 pm

In British English Auto or Automobile is rarely, if ever, used in reference to a car (a contraction of carriage). Sometimes 'Motor' is used, "My motor broke down yesterday." but that is also quite rare and means the complete device, not just the engine. "My motor broke down yesterday, the brakes failed." Unusual but is occasionally used.

So in this context an auto-transformer has nothing to do with cars, automobiles, buses or trucks. You could say that you put 220V in and automatically 110V comes out. I don't know. English in all its variations is a minefield!

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Re: 1960s Open Reel tape recorders

Postby Klaas Robers » Mon May 22, 2017 7:03 am

You know the word "Auto Mobile". It is a "Mobile" thing that moves itself. Auto = Self, a "self mover". In the Auto Transformer the primary itself is also the secundary. That is why a transformer with only a primary, with a tap, preferably half way, is called an "Auto Transformer".

I used this rather recently, when I bought a Heathkit SB630 station consote (see below) via Ebay.com, so from the States.This thing was 115 volt only and I built in a 115+115 volt to 12 volt ring core transformer. The center tap (115 volt) I used to feed the electronic 10 minutes timer (a tube circuit) and the 12 volt secundary to feed the mechanical synchronous motor clock from. The latter needs a real 60 Hz to run on time. A PIC generates the true 60 Hz sine wave.
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Wed May 24, 2017 2:08 pm

While on the subject of 60Hz, I came across an article which used a rather novel approach to generating 60Hz in a 50Hz country, or the other way around. In most developed countries the long-term frequency of the mains supply is very stable, short-term (within minutes or hours) it may be off a little due to varying loads. This is corrected by slightly adjusting the generator/turbine speed.

The idea is to full wave rectify the 50Hz or 60Hz, both these produce harmonics and both contain a 300Hz and 600Hz component. This is then filtered then squared into a 600Hz square-wave. If you want 60Hz you divide by 10, if you want 50Hz you divide by 12. Then filter this to get an approximation to a sine-wave then a simple power amplifier (TDA2040) to feed a small 220V to 6V (or 110V to 6V) transformer used in reverse. The frequency is locked to the same reference as the original supply. Quite a simple idea.

This could also be done by using a phase-locked-loop (PLL) and often is.

This was built to drive mechanical clocks that used synchronous motors, so only a few watts were required.

I have the article in HTML form but it's still covered by copyright, the page on the site has gone otherwise I would simply provide the link. If you wish a copy PM/e-mail me. UPDATE..the site has moved, here's the link...

http://sound.whsites.net/clocks/freq-changer.html

Steve A.

The article isn't that old but today an alternative method would be to use the once-per-second pulse out of a GPS receiver.
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Re: 1960s Open Reel tape recorders

Postby Klaas Robers » Sun May 28, 2017 8:27 am

Steve, this is how I did it:

Schema 60Hz-bron-2.GIF
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The X-tal of the PIC can be tuned and the PIC generates a PWM signal of a pure sine wave of 60 Hz.

The TDA1519 is a 2 x 11 W stereo amplifier IC for car radio, but one channel gives an inverted signal, the other a non inverted signal. So it can also be used as a 22 W bridge amplifier, which I did.

The X-tal frequency is divided by two and available at a BNC-output. Because 60 Hz is not a subharmonic of 20 MHz the generated frequency can only be a close approximation. But if the 20 MHz is tuned to 20.000 032 MHz, the 60 Hz is correct. So the 10 MHz should be 10.000 016 MHz.

I check the 10.000 016 Hz using my frequency counter. But 10 MHz on 1 Hz precise..... the TCXO of the counter is hopefully 10^-6. That is why I built a GPS stabilised 10 MHz source. Now I can check the counter just before I adjust the 20 MHz X-tal oscillator.

With all this the clock runs within a few seconds per month precise. That is better than what ever power grid.
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Sun May 28, 2017 1:44 pm

It might be an interesting exercise to measure how precise your power-line frequency is. Not that hard if you have a GPS receiver with a 1PPS output. Square-up the 50Hz feed it into a counter in a PIC. Also feed the 1PPS into a second counter. In 24 hours there'll be 50x60x60x24 cycles, 4,32 million cycles. 5.184 million for 60Hz. That's an easy 3-byte binary number.

The 1PPS is also counted and stops the other counter when it reaches 60x60x24 seconds, 86,400, one day. So it should be able to resolve something like one part in that 4.43 million (or 5.184 million). Store the results in EEPROM for download once in a while. You have to flag power-outages though, however short.

Cumulative long-term errors by simply adding each days count over a longer period of time and crunching the numbers in Excel.

If you full-wave rectified the 50Hz (or 60Hz) to 100/120Hz you''ll double the measurement accuracy, it's still a 3-byte number.

I'm not going to bother doing that, I have no faith in the power generating authority here.

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Re: 1960s Open Reel tape recorders

Postby Klaas Robers » Sun May 28, 2017 7:49 pm

Oh Steve, we have an radio-alarm clock here that runs on the 50 Hz. It slowly deviates from the precise radio time and after weeks it may return more or less. So every morning at 7.00 I hear the inaccuracy of the power grid.....

On the other hand, I have 4 clocks running on DCF77. Those are my time references. I should see if I can make an output pulse once a day on one of them and make a period-counter on the mains frequency, which is stored once per day at e.g 24.00.00. Would be nice.....
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Mon May 29, 2017 2:45 pm

Yes, that's another way to get a precise once-day-pulse. It depends where you are. In most of northern Europe you should be able to receive an LF time signal broadcast. The US and Japan too. But here there's nothing like that, so it's GPS or nothing.

I flew from Bangkok to Chiang Mai in the north of Thailand some years ago. My travel alarm clock was able to decode any LF time broadcast. Once I got to my destination I realised that at 30-odd thousand feet it must have picked up the JJY signal from Japan as it was two hours ahead. At those low frequencies the aircraft fuselage offers little attenuation.

I don't use it any more, the mobile phone acts as my alarm clock everywhere, even at home.

Instead of modifiying/expanding one of your DCF77 clocks, a more convenient way may be a GPS module, there are so many on ebay and the like at around US$20 with the 1PPS output as well as the NMEA ASCII data which you don't have to use it if you have no need for it...e.g.

http://www.ebay.com/bhp/gps-module

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Re: 1960s Open Reel tape recorders

Postby McGee2021 » Mon May 29, 2017 3:12 pm

Klaas Robers wrote:Oh Steve, we have an radio-alarm clock here that runs on the 50 Hz. It slowly deviates from the precise radio time and after weeks it may return more or less. So every morning at 7.00 I hear the inaccuracy of the power grid.....

On the other hand, I have 4 clocks running on DCF77. Those are my time references. I should see if I can make an output pulse once a day on one of them and make a period-counter on the mains frequency, which is stored once per day at e.g 24.00.00. Would be nice.....


I read somewhere, perhaps a college text book, that there are international standards of accuracy that state that the frequency of the power grid can not deviate within .01 percent of their set frequency, whether it be 50 or 60 Hz, because of electric clock and appliances! It also stated that the frequency must be checked every 3 seconds, and if off from standards, there could be legal charges put up against the power company by the people that put the standards in place! Here in the US, the standards are supposedly even more strict. One good thing about it is that it could be used as a mains frequency controlled synchronization of your televisor...
John Logie Baird was obviously the man who sowed the seeds but did not reap the harvest.
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Fri Jun 02, 2017 1:09 pm

So, back to the tape recorder. The thin sewing machine oil has done its job and the rotor is now free. There's still a little bit of drag there but it spins easily by hand on the 3mm shaft. I'm going to keep applying the oil for a few more days before I apply power. In the meantime I'll get on with oiling/greasing the other mechanical parts. There didn't seem any point in doing that earlier if the motor was a non-starter.

I'm in two minds whether to retain the original valve/tube circuitry or replace it. The machine is not rare or valuable, or even that good when it was new. The original electronics uses quite a few inductors in the equalisation circuits, both record and playback. This is typical of the period. Today it's generally done with op-amps and a few passive components. The exception is the bias/erase oscillator, here you generally need a coil/transformer arrangement, especially in this case as the heads are likely to be high-impedance to suit the original circuitry. I have plenty of time to decide though.

I'm not planning to use it for speech or music, it'll be a test-bed for all sorts of things, specifically what...watch this space.

However, if I were to use it for music I would convert it to stereo, it has four-track erase/record/playback heads. In which case the original circuits would have to go.

The current status is below...

Steve A.

Studying the circuit diagram and the real thing there's a horrendous multi-pole switch on the PCB which changes the machine between playback and record. Those old enough in the UK will remember those dual-standard 405/625 TVs. They too had a similar arrangement...about as reliable as the British summer. In a word - horrible, awful, crap...OK, that's three words. The more I look at this the more I'm leaning towards gutting the thing.
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Re: 1960s Open Reel tape recorders

Postby Harry Dalek » Fri Jun 02, 2017 7:20 pm

Re purposing interesting ~i am wondering what a reel to reel tape recorder with new electronics could do ... :?:
A idea way beyond me was always as with the very first video recorders 405 line ? running the tape at high speed for a few secs of video //very impractical but would be extremely interesting .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: 1960s Open Reel tape recorders

Postby Steve Anderson » Fri Jun 02, 2017 7:45 pm

Yep, here's a pdf of VERA, the BBC's first Vision Electronic Recording Apparatus. The tape speed was 120ips (inches per second) and the immense tape reels could only hold 15 minutes of video and audio. It was first used on-air in 1958. 120ips is 32 times the speed of the average domestic audio recorder at the time (3.75ips), or 64 times the speed of the Compact Cassette developed in the early 60s (1.875ips). Added later...actually the tape speed was 200ips! Slightly over 5 metres/sec. My mistake.

I also have two mp4 video files covering the same subject but they're too big to upload here, around 25MB each. If you wish a copy of them send me an e-mail with your e-mail address and I'll send them on. Make sure your in-box has at least 50MB of space free and can accept single files of at least 25MB each.

Steve A.
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