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GPO linesman 250A linesmans sets

Started by gpo706, October 18, 2009, 10:20:46 PM

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gpo706

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150377552318&ssPageName=STRK:MEWNX:IT
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270467797964&ssPageName=STRK:MEWNX:IT

( dead links 08-04-21 )

The nice one was £5, the scabby one I bid £7 max was beaten it went for £7.50 then the person retracted their bid and the seller offered a second chance for £7.

Needless to say the £5 one is in better nick than the £7 one, both been batteried up (2 x 1.5 V D cells)and both work so quite a happy bunny.

The dearest one (£7) had electrical tape wound round the handset and I feared the worst as I pulled it off, thinking a broken handset, but no, just there to to keep the lower grip on the "on" position when using it, handset is fine and after some lable remover got 30 years of gummed up tape off, though it is still seems to be hard wired to constant transmit, so donno why it was bothered with taping the handset switch in.

Here's the science bit...

http://www.britishtelephones.com/t250.htm

If you look at the link you see a battery box, it basically houses 2 x D 1.5 V cells and I can get a housing and a clip for these for peanuts through local electronics store, but still need to figure out how the £7 one has constant "on" I think its been rewired somewhere inside.

I tried them both on the the oscilliscope and they jump up and down from plus to minus 3V when the handset is used and the generator and dial make the scope fly off the scrreen.
"now this should take five minutes, where's me screwdriver went now..?"

Phonesrfun

Scot:

By looking at the diagram, it would appear that the way to bypass the switch and make it always on would be to either bend the switch so it was always as if it were being pressed or to jumper between the switch contacts at S" and S', or between S" and M1.  I have never dealt with one of these, but presumably there are screws that allow the push-to-talk switch to be removed from the handset handle so you can see what's going on.

-Bill G

Phonesrfun

After some more thought, I was also wondering if all those years of the button being permanently taped down if a couple of mechanical things might be the case.

First, maybe years of dirt, grime and other crud have gotten in the shaft of the button causing it to stick in the "pressed" position.  Maybe a little lubrication on the shaft of the push to talk switch would be in order.

Another possibility is that with it taped down for so long, maybe the switch spring is just permantly bent in the on position due to the spring being compressed all that time.  It may need to be bent back out to the off position.

Just some thoughts, anyway.

-Bill G

gpo706

Yes Bill, makes sense, definately worth exploring both your ideas, I suspect the spring has been flattened.
"now this should take five minutes, where's me screwdriver went now..?"