Using Mimeo 1 in UK, Europe or Australia - Newbie question

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Joined: Aug 16 2015
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Hi,

I am new on here. I am planning to build a Mimeo 1, Apple 1 replica. I was wondering if anyone had any experience or views on using a Mimeo 1 on a 230v 50Hz system (rather than the 115v 60Hz the Apple 1 was designed for).

The recommended Stancor or Triad transformers are obviously no good as they are for 115v systems. I have seen what I think are a number of potential 230v alternatives, but wondered what others have used and whether anyone has any recommendations.

My bigger concern is whether the power supply circuitry on the board can cope with the 50Hz AC system. My understanding (and my understanding is very basic) is that for 50Hz mains, a power supply would theoretically require a 20% larger filtering capacitor than for 60Hz mains given the correspondingly longer discharge time on each cycle. Has anyone experienced any problems running the system on 50Hz mains and has anyone needed to change any of the capacitors?

Finally, I assume that the composite video output of the system is at 60Hz whereas many monitors produced for the UK and European markets were designed for a 50Hz signal. Has anyone had any issues source a suitable display? Again any comments would be greatly appreciated.

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Joined: Aug 25 2014
Posts: 20
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Regarding your last question, ideally you want a monitor that accepts an NTSC signal, which was the North American 60Hz standard. The 50 Hz standards in other parts of the world were PAL and SECAM. These three standards are completely incompatible (and not just from a line rate standpoint).

There are inexpensive video converters on the market though, and that might be your best bet (search eBay). The Apple 1 NTSC is a bit out of spec, so there is some risk that a converter may have a problem.

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Posts: 64
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

From a power supply point of view a 60 hertz transformer will work at 50 hz and the increased ripple is not an issue since all four rectified supplies pass through voltage regulators which will clean up the ripple.

For the video, why not get a 60 hz NTSC monitor and add an external 230 to 115 volts transformer ?
I think this will be simpler than trying to match Woz's non-standard NTSC video to a PAL or SECAM system
The power supply in the analog NTSC monitor on the other hand might need some additional capacitance in the power supply to cope with the 50 hz ripple.

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Posts: 2413
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Hello Lazarusr,

since this is a topic that might be of interest to several european users
i will cover this a bit more in detail for better understanding of all that users.

Some part of the questions have been answered in the replies above.

For better understanding just view the picture below
( and that users that ask for better and higher resolution to view better
the details the same picture is availiable with far higher resolution at:
http://www.appleii-box.de/applefritter/Apple1Power.jpg )

Line A) displays the situation at countries with 50 Hz
and line B) displays same situation but with 60 Hz.

To get better view to details the sections are split to 1/10 of a second.
This results to a display of 5 complete waves at 50 Hz and to
6 complete waves at 60 Hz AC.

For better explenation i added at C) also a part of the circuitplan of the
Apple 1 power regulation focused to the + 5 Volt branch - but at the other
branches are similar.

At (1) the section before the rectifier diodes are displayed. There are
complete AC sinewaves like they come from the walljack. After passing the
rectifying diodes the negativ sinewaves get kind of "inverted" and at (2)
behind the rectifier diodes you would see at 50 Hz within the period of
1/10th of the second 10 half-sinewaves and at 60 Hz the total of 6 sinewaves
in the same period of time would add up to 12 half-sinewaves.

At this point (3) that voltage enters the section where the large electrolytic
capacitors get charged and discharged. I display this section 2 times because
i wanted to spot out the real influence of the size of that capacitors.

If you operate the powersupply at 50 Hz the period between charging and
discharging of the capacitor is extended compared with the 60 Hz with shorter
charging and discharging time. But with average load at the output this
will cause nearly no issue. The issue might get recognized the larger the load
gets at the output of the powersupply because higher load causes faster
and more discharge at the capacitor. This would result overall to a
drop of availiable average voltage at the input of the voltage regulator
and in general the voltage regulator would get in trouble as soon as the
input voltage gets less than 3 Volts more than the output voltage.

At the Apple 1 this is no problem because the rectified voltage behind
the diodes sum up to more than 12 Volt and therefor even a slight drop
by heavy load at the output won´t have efeect to the regulated voltage.
Similar is valid to the 12 Volt branch where voltages of nearly 20 Volt
are availiable. Therefor the electrolytic capacitors at the side before
the regulators won´t affect the operating condition of the Apple 1.

Rather more the electrolytic capacitors behind the regulators might
play a role in the game. The Apple-1 pulls avarage 1,2 Amperes from the
powersupply with the cassette interface inserted ( and that will be the
general condition ). The 22µF capacitors are quite close to the limit
and it might turn out to be a good idea for those who intend to work
several hours with the Apple-1 to use instead 47µF or 100µF capacitors
instead - allthough they are not like originally specified.

A real far more important issue might turn out to be examining the filtercaps
used across all over the Board ( all 100nF = 0,1µF diskcapacitors )...
You should be sure to check out their ESR values.... if they have bad
values choose capacitors from another manufacturer .... There is quite
a lot of "noise" on the supplyvoltages and it´s really important to
get a good filtering to get rid of that "noise" ( spikes ).

The far more important part of the question will be answered below the picture.

In the lower part of the picture i have added some partial pictures from the
circuitplan. It would exceed this posting to explain all the details how the
Apple 1 generates its videosignal. But this brief overview will help to
understand the answer to the second part of the question.

Section D) displays the main part of the base timing of the Apple 1.
The core is the crystal oscilator with the 2 gates from the 7404 at
location D12. It passes that 14 MHz signal to the 74175 which devides
that frequency and that 74175 drives with the clocking signals nearly all
chips of the Apple 1. At pin 6 it issues the base frequency of the videosignal.

That base frequency is mixed at the base of the Transistor Q5 with the
datasignal which is coming from the pin 13 of the 74166 at location D1
( see section E) ).

The datasignal is driven by the dotrate signal from pin 6 of the 74166
at position D1.
This signal is passed over to the 74161 at position D11 and that chip
drives one part of the videosignal and the other part is the chain of 74161´s
at locations D7, D8 and D9 as a kind of chain. one part exits the
pins 12, pin 13 and pin 14 from location D8 and enter a kind of multiplexing
"add-chip" at location D2 ( The character ROM 2513 ) and the other part of
the data-information is resulting from the chips at location C3 and C4.

So you may view the 2513 at position D2 ( marked F) ) as a kind of dot
string from data "adding chip" - in fact its the character ROM and it issues by its bytes
row by row the bits to display a character at the screen - and its additionally driven also by the
other data from Chip at position D8 - adressing the bytes of the character.
Then the missing parts of the signal are added at the 74166 at position D1,
before the nearly complete signal gets joined with the base video frequency at the base of
Q5 and then the sum of that 2 signals is passed by the Q5 to the videoconnector.

So the influence of the supplyvoltage and the frequency of the powersupply
doesn´t have any relation to the videosignal of the Apple 1.

But one thing has an influence - the frequency of the monitorpowersupply.
It´s not driven by a crystaloscilator and therfor it often has some unfortunate
liability to the frequency of the netpower AC. This might result to the problem
that a monitor might not be able to catch the horizontal sync signal with
resulting transverse shifting of the picture.

Therefor if you live in Europe it might become usefull to search for an
old monitor that offers a switch to change between NTSC and PAL -- allthough such
monitors are realy rare.

Finally to the question about the transformers.
Of course it´s useless to use the Stancor transformers in countries with
230 Volt AC undless you use a "stepdown" transformer from 230 Volt to 115 Volt.
But there is no win in this configuration. I just used modern toroidal transformers
due to the fact that they have better efficiency and are smaller and have
less strong magnetic field distribution.

sincerely
speedyG

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Posts: 56
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Thanks speedyG! That is an amazingly detailed, helpful and thorough response. In terms of the power supply issue, although the level of detail is way beyond my ability, you have confirmed what I suspected namely that the system should be OK, as long as it isn't used under load for a prolonged period.

In terms of the video, as I understand what you are saying, unless I can find an NTSC compatible domestic monitor (unlikely) it may be just a question of trial and error if a PAL monitor will be able to display a stable signal.

That being the case, it would be really helpful if you could let us know what monitor you are using.

I note that you are using modern toroidal transformers – which is the route I was probably going to go down. Again, it would be helpful if you could say which make and part numbers you actually ended up using.

Many thanks again.

Robert

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Posts: 382
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Note that I have a TAXAN brand monitor that has worked for both Apple generated PAL and NTSC. I know this because I acquired an Apple II that was configured for PAL (including crystal), and it took me a while to realize it, as I happened to initially use that TAXAN monitor with it. The TAXAN wiki pages says they operated in the UK. I wonder if they were designed as dual purpose, or if mine is an exceptional unit.

Here is a picture of it.
http://www.willegal.net/blog/wp-content/uploads/2010/01/video.jpg

regards,
Mike Willegal

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Posts: 56
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Yes, they were big in the UK. In the early 1980s I used to work in a shop that sold electronic components and home computers – most notably the BBC Microcomputer (which was huge over here). We sold a lot of Taxan monitors.

I am trying to source a composite monochrome monitor from that era that claims to have dual NTSC/PAL compatibility. It's not easy because detailed data about monitors from that era is hard to come by and, in any event, there is not a lot of choice. I think I may have found one though – a Philips BM7522. I have also identified another possible candidate – a Zenith ZVM-122-EA. If anyone has any knowledge of these, comments would be much appreciated.

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Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Well i have several Monitors.
one is from Blaupunkt.
Its a analog RGB Monitor snd it has the option by switch to operate in various modes.
Another one isfrom Commodore Mod.1802
also capable to display color.
then i have one from Zenith.
That one os Monochrome and i like it, because it has the very extended range
of adjustments. Its capable to handle any signal not bothering if its PAL or
NTSC and how bad that signal is..... up till now it was able to get a correct
display in every case... thats the one i also favor in use with the Apple 1
and as far as i remember this is a valid statement with all Models from Zenith.
Then i also have a Apple IIGS color monitor and somwhere in my dungeons there
is also a Apple III Monitor but i haven´t used it in the last years.
sincerely
speedyG

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In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

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Posts: 2413
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Well i have several Monitors.
One is from Blaupunkt.
Its a analog RGB Monitor and it has the option by switch to operate in various modes.
Another one is from Commodore Mod.1802
also capable to display color.
then i have one from Zenith.
That one is Monochrome and i like it, because it has the very extended range
of adjustments. Its capable to handle nearly every signal not bothering if its PAL or
NTSC and how bad that signal is..... up till now it was able to get a correct
display in every case... thats the one i also favor in use with the Apple 1.
Then i also have a Apple IIGS color monitor and somwhere in my dungeons there
is also a Apple III Monitor but i haven´t used it in the last years.
sincerely
speedyG

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In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

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Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

You wouldn't happen to know the model number of the Zenith? Is it one of these: http://www.1000bit.it/ad/bro/zenith/ZDS-122-123S.pdf?

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Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

ZVM 123-E

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Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Excellent. I have been looking at one of those. There's a refurbished model available for sale in the UK at a reasonable price.

Thank you so much for your help.

Joined: Nov 20 2004
Posts: 41
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Hi lazarusr,
I used 2 transformers available here in Austrailia from JayCar an electronics shop.
I have included scans of the boxes that they came in, as I'm planning to build another power supply.

You will have no problems with 50 and 60hz systems as far as the power supply is concerned.
I have used a Mimeo-1, an Obtronics Apple-1 and a Mike Newton Apple-1 clone as well as repairing a Mimeo-1 mother board (that earlier caught fire-tantalum caps were supplied as the bypass caps) on the same power supply with no problems.

For the monitor I use what works on an Apple II, in fact I use an Apple II monitor and a Monitor III (originally for the Apple III but many apple users use it in an Apple II without problems). I found no problems with distorted video at all. Just get a monitor that accepts a composite (not component) video input. Also there are some fancy video converter units in China Via EBAY that you can use if you cannot get something with composite video input.

One suggestion: Build your power supply into an old AT PC power supply metal box. Gut everything except the 240v switch and the 240v plug. That way it ends up in a nice safe metal box that is earthed for safety, and the power cord that came with the old power supply can be used.

Best wishes.
[inline:attached_image_#][inline:attached_image_#]

PS: Hmmm...can't find a way to attach the transformer photos and details. All help greatly appreciated

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Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question
Joined: Nov 20 2004
Posts: 41
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Thanks tolderlund for the link to SpeedyG's guide to insert content in my response to lazarusr.
I can now do it.

I have been a little concerned about mains voltage wiring and the possibility that the home built power supply might be unsafe.
I have a solution that uses an old AT (or similar) power supply already with the hardware in place to go from the mains to the PS box. It might even have a mains switch, and it should have the IEEE mains socket. This means that the only mains wiring to be done is to connect the IEEE socket outlet to the transformers.
Warning: mains voltages are potentially lethal, in some countries, this has to be done by a licensed electrician.
Do not attempt this if the above applies, or you do not know what you are doing.

Here is an Apple 1 power supply idea that uses old hardware that you might have around...

These are the 240V transformers from JayCar:

Next photo shows transformers in the PC AT power supply box:

Finally the finished product in a closed earthed metal box:

Regards...

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Posts: 56
Re: Using Mimeo 1 in UK, Europe or Australia - Newbie question

Thought I'd show what I ended up doing in terms of the power entry module.

I found this case on eBay which had a suitable vintage look. The switch, power light, fuse holder and mains connector are all period appropriate vintage parts.