Invertor frequency adjustment

In a previous life, I was a Post Office Telex/Telegraph/Teleprinter engineer for over 20 years from about 1969 and did maintenance, overhall and faulting of the Teleprinter 15 ( that was the BPO's designation for the Creed 444 -

15A for basic machine, 15B for machine with punched tape facility) amongst others ( Creed 11, 7B, 7E, 23. Transtell, Puma etc etc).

I also passed my RAE in 1967 though was never licensed ( it was the Morse test for an 'A' licence that stumped me and 'B' licence UHF equipment was very expensive at the time for a youngster). Also, as a 16 yr old in 1967, other things, female in nature, distracted me for many years.

Once settled down and married, and when computers became affordable for the masses, I used to monitor RTTY ( mainly news agencies on HF ) using a Vic

20, a Sony short wave radio and a home built RTTY demodulator ( The Maplin one of the time ).

News agency RTTY transmissions re the first Gulf war ( was that 1991 from memory ?? ) were indeed very interesting and it was especially interesting to see how they varied, considerably at times, from the output of the mainstream UK News channels at the time.

The phrase and header 'NOT FOR PUBLIC RELEASE' comes to mind.

Maybe they thought that their HF RTTY communications were private and no-one would be monitoring. I was and often - it became a bit of an obsession.

As well as the live screen display on the VIC 20, the RTTY feeds were fed to an old Transtell teleprompter that I had acquired on the second hand market for cheap.

My Vic 20 was a VERY self modified Vic 20 as, as standard, they don't have a printer interface.

In fact I still have that VIC 20 - saw it a few weeks ago, and the RTTY demod I built, unused for donkeys years, in the shed covered with years of dust.

Got a bit carried away reminiscing there - back to the subject ( almost ).

I thought that, from research at the time, someone had produced a gear set for the 444 to allow 45.5 baud working on 50 Hz mains supply.

Searched tonight and found this

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which says that there was available a governed motor variant for the 444. No doubt like hens teeth now though.

There used to be, many years ago, The British Amateur Radio Teleprinter Group ( BART it was for short ), but they changed their name with the onset of things digital many years ago and I cant remember what they changed it to.

In fact I used to subscribe to the BARTG monthly magazine at the time ( I'm a hoarder of things technical and wouldn't be surprised if I still have them - somewhere ).

But I do nothing in this field today or for many years.

HTH

Reply to
Booty
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Rather than use a modified inverter here's another idea, coning from my dim and distant past....

I recall varispeed on a couple of EMI TR90 tape machines in the early 70's was done this way. The synchonous capstain motors motors were fed with vari frequency 240V via a variable oscillator, a pair of quad audio power amps in parallel, and a backwards mains transformer. They needed about the 50 watts that you are talking about, which should be quite achievable with modern power amps. You've almost certainly got a sine sig generator that will do the job too, athough these days a laptop is probably as easy.

Charles F

Reply to
Charles Fearnley

Gawd knows...

Adding a C or R to a cheap invertor is some what cheaper and less overkill. B-)

Reply to
Dave Liquorice

Yep August 2, 1990 - February 28, 1991. I was out there for Christmas

1990. That show got nominated for the RTS Television Outside Broadcast of the year but didn't win. B-(

I used to monitor the news transmissions as well around that time, a facinating different slant on the news. I guess the easy availabilty of Al Jazeera and other non US/UK news networks makes getting an alternative view a little easier these days.

They didn't change a great deal from "British Amateur Radio Teleprinter Group" to "British Amateur Radio Teledata Group" both having the acronym BARTG. They did have a 45.5 gear but sold out yonks ago.

Reply to
Dave Liquorice

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