GPO 1/764 pushbutton - A surprising oops moment!!

[twocvbloke]

I haven't a clue how a previous owner broke that off, I mean, they'd have to be a complete idiot to not know how to use a flat-headed screwdriver to remove a screw!! As for the missing retaining nut, that's common, I just had a random thought on how to replace it, and it seems to work nicely...

[twocvbloke]

I just got woken up mid-dream right at the perfect point, I'd come up with a new dial card with a suitably nerdy number that went along with the unreadable original; 01-486-6502... 

[tubaman]

Getting a Transmitter 21A is a nice bonus as they are getting quite hard to find now.

[twocvbloke]

I've a few red 21As around, this blue one is a new one for me though, even though they're technically the same thing...

[twocvbloke]

Totally random picture but I just noticed my Twitter posts number, rather amused me... 

[tubaman]

I've a few red 21As around, this blue one is a new one for me though, even though they're technically the same thing...

The red ones are arguably more useful as you can use the inner 'capsule' in other phones, but they're all far better than the carbon granule versions.

[twocvbloke]

So long as the red ones actually had the correct innards, as three of mine turned out not to:

http://www.classicrotaryphones.com/forum/index.php?topic=7254

Only just remembered about that little discovery... 

[Stormcrash]

I think you're right. I gather a Trimline only lights up when off-hook. I don't actiually have one (yet) so can't tell you much about it.

Yes, Trimline phones only light up when the phone is off hook, with the LED models being line powered.  Later post breakup Trimline phones with memory dial functions do use some line power to keep their memory going, though I don't know the specifics of how they trickle this from the line power.  They do not have batteries, but a capacitor in the phone will bridge the memory through brief power interruptions like unplugging and moving the phone.

[twocvbloke]

Just been driving myself nuts with wiring this phone back up inside, it's really been messed with in the past, had to pull it all and re-do it from scratch, then found it was missing an auxiliary gravity switch (19B-1) "to control the push-button unit" as the N864 diagram states, thankfully I bought some 36A-1 switches last year, there seems to be conflicting info as to which switch is what poles-wise, but as the dial only needs a single-pole changeover switch, the 36A-1 will work nicely...

Next step, battery, I daren't use a 4.2v Lithium Polymer battery I have spare, just incase something goes wrong, so, I'll have to have a look about to see what's available on ebay...

I'd take some pictures of the wiring, but, I'm so sleepy right now I'm falling asleep as I type, I need to go to bed!!! 

[twocvbloke]

Finally got around to getting the additional pictures, 1st showing the Switch 36A-1, took a fair old amount of adjusting to get it to work in time with the main hookswitch, plus a view of all the extra wiring required to operate this particular dial.

2nd, the terminal arrangement as originally wired per N864, with the only difference being the 3.3k resistor in line with the ringer coils.

3rd is showing the back of the extra terminal strip showing a capacitor (I believe) between a couple of terminals.

And lastly 4th is showing some battery leakage damage I didn't notice previously, but it's nothing that really concerns me that much...

Plus an extra bonus clip of pressing the buttons, sadly my mobile isn't that good at picking up the rather joyously satisfying feel of the clicks the buttons make, but it's still something to watch nonetheless... 

https://www.youtube.com/watch?v=HmP05ZKPgc0

[Jack Ryan]

Is the relay a part of the "push-button unit assembly"?

Is there a circuit for that?

Thanks
Jack

[twocvbloke]

I believe the relay takes the place of the pulsing contacts in a regular dial, so the phone presumably clicks as it dials the number, I haven't tried it out yet as I've yet to power it up with something suitable...

[Jack Ryan]

I believe the relay takes the place of the pulsing contacts in a regular dial, so the phone presumably clicks as it dials the number, I haven't tried it out yet as I've yet to power it up with something suitable...

Ok, I thought it might have been the ON contacts. I don't remember seeing a relay on other LD button phones. But then, I don't think anyone else used a battery either.

No circuit for the keypad logic?

Jack

[twocvbloke]

No circuit for the keypad logic?

So far I've not found any diagrams for the keypad, as I too am curious as to how it works, it appears to be all individual transistors providing the logic as I can't see an IC of any kind on the keypad (not that there would be given the era, ICs would probably have been quite expensive in the 70s and reserved for computers only), the only circuit I have available is the one from the N864 diagram, which only depicts the inputs to the dial which is just a big empty box... 

[Jim Stettler]

ICs would probably have been quite expensive in the 70s and reserved for computers only),

WE made some trimlines with tone generating chips as early as 1968-69. These were both 10 and 12  round button sets.
Most of the early handsets were potted TT pads, but they concurrently made  the tone generating IC pads .
By the mid 70's many of the round button sets were being rebuilt with IC's.  There were many sets that were rebuilt with potted TT pads as well.
The earliest tone generating IC chips were clear

The picture phone project was concurrent and  also used a lot of IC chips.

Jim
As a side note regarding trimlines, the round button sets seemed to continually  evolve and the boards  changed quite a bit. You can find a lot of variations in the handset layout. The handsets on square button sets pretty  much stayed the same, tho they were simplified as time went on.