[GreenKeys] TT-4C We have action!

[Greg Arnoldussen]

With the assistance of my friend we managed to "manufacture" a DC voltage of 105 VDC for the loop supply.  The transformer we had handy had the choice of inputs of 400V or 230V and outputs involving combinations of 55 and 60V on two windings.  By hooking in 240 VAC to the 400V input we then chose 60V + 60V on the output and used a large capacitor with diode to rectify to DC.  As I have since learnt, AC is quoted as RMS but DC is at peak current and the difference between the two is about 1.4.  Therefore 120 VAC is not the same as 120 VDC, it is actually closer to 170 VDC.  Therefore, as the mains 240V was going into 400V that was a factor of 0.6 so that brings 170 VDC back to about 100 VDC.  Indeed, when I measured the output it came to 105 VDC, not quite 120 V but it seems to be OK (read below).  If required we can re-configure to achieve 140 VDC but I thought to play it on the safe side.  Also the breadboard is safely housed in a plastic box,
 and the transformer has no exposed wires.

Upon connecting to terminals 1 & 4 I got nothing on the milliammeter despite turning the line knob, yet the multimeter was reading 105 VDC across them. Yes I had blown a fuse.  Just in case the original fuse had been blown previous to me buying the machine I tried another (250 V 0.12 A) and it blew too (these fuses have a very fine wire and it is quite difficult to see - checking with the multimeter resistance confirms if it is OK).  At this point I measured the rheostat attached to the line increase knob and worked out that at maximum resistance it read 2500 ohms which was exactly correct.  Just one problem....silly me had the knob turned fully clockwise and effectively offering no resistance!  This is why fuses exist - to stop idiots like me blowing things up!  I know a few people here on greenkeys have already told me to do the exact opposite of what I did, including the manual, but for some reason I took "line increase" as an increase in
 resistance.  Nevermind, I still had an extra fuse so THIS time I turned the line increase knob fully COUNTER-clockwise, turned on the loop supply and slowly backed off the resistance by turning clockwise.  Low and behold the needle on the meter started rising and I stopped it at 60 mA with the switch to "DC".

At this point I started the motor and the TAT TAT TAT noise ceased with just the (much quieter) whirring of the motor left.  I set the range to 65 and adjusted the armature until I could get the keyboard to type.  It all works perfectly!  Every single key works including the BELL and STOP key.  The BREAK key starts the motor after pressing STOP.  The only thing I noticed (and this may be because it has been so long since I used a manual typewriter) was that it felt a bit clunky - I doubt I could type as fast on the TT-4C as I can on this laptop, however because the pictures in the manual are very difficult to see there is a good chance I have not fully lubricated every component.  I have also tuned the motor.

So all in all a very productive weekend.  After completing the clean up and lube of both machines I will hook them up and see if I can get them to communicate.  The final step will be to connect to the PC and supply a feed when I have an appropriate interface available...I have already had a lot of emails from everyone concerning this and I will be relying on more advice in time to come as I can see this as being the most challenging of all.

Thanks to everyone for your help this weekend (Steve, Duncan, Don, Jim and anyone else, my apologies if I have forgotten anyone).  Much appreciated, thanks again.

Greg in Wangaratta.
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