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Tesla T57

Started by tubaman, December 21, 2019, 06:54:23 AM

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tubaman

I've just got this Tesla T57 from eBay - https://www.ebay.co.uk/itm/Black-Bakelite-Tesla-Eastern-Block-USSR-Telephone-P30-/254445483875.
( dead link 06-14-21 )

"Black Bakelite Tesla Eastern Block USSR Telephone, P30. Condition is Used. Overall good condition. We tested on our line and its working, but we can't guarantee that it will work on your line. Dial is OK. Black dial. Most likely from Czechoslovakia.  Looking in the vent holes underneath it could be missing one of its bells, although currently rings with a distinctive sound."

It's a phone I've been after for a while and was only £10 + £6.50 postage (about $21 total) so I'm pretty pleased with that.

The seller also had another that I think was a T58. As this one had the earlier style black dial and cloth handset cord I went for it in preference to the other one.  With hindsight perhaps I should have bought both?  The other one is at https://www.ebay.co.uk/itm/Black-Bakelite-Tesla-Eastern-Block-USSR-Telephone-P30-/254445487579. ( dead link 06-14-21 )

Mine is in pretty good shape, with only a small chip on the left of the case. Most of these I see are pretty knocked about, so this one is pretty good. It also has a bell missing, which was declared in the listing, so I need to look through me spares box to see what I have that'll fit.

I have spent a bit of time sorting the wiring as it had been 'converted' and was not right at all. The nearest diagram I could find was from a T58 (http://www.classicrotaryphones.com/forum/index.php?topic=22896.msg230168#msg230168). I'm a bit puzzled by it as it looks like the off-normal contacts put a dead short across the line when you dial - is that correct or am I misreading it?
:)


countryman

Quote from: tubaman on December 21, 2019, 06:54:23 AMI'm a bit puzzled by it as it looks like the off-normal contacts put a dead short across the line when you dial - is that correct or am I misreading it?
:)

I guess that is the way it is supposed to be. The diagram is drawn in a different way than inside a german W48 for example but actually it's a very similar beast.
The off normal contact shunts the network out of the loop so that no dial clicks will be heard. Also, the resistance of the network is taken out of the loop to allow the strongest possible dial pulses, important on long lines.
In this setup DC flows through the induction coil. When it's shorted out, the magnetic field breaks down and induces a voltage leading to a popping sound in the receiver. Therefore the rectifier element is essential on these designs to limit the voltage over the receiver. It's 2 selenium diodes in anti-parallel, limiting at around 400 millivolt. This element also appears in german phones with similar circuitry.

You made a good choice, the other phone most likely had a later replacement dial.

tubaman

Quote from: countryman on December 21, 2019, 07:24:18 AM
...
You made a good choice, the other phone most likely had a later replacement dial.

Thanks - it was the dial that turned me towards the one I got. I felt the other dial didn't sit as comfortably with the rest of the phone as the black one does.
I suspect my one has been through the refurb process - hence the extra labels on the base.
:)