[VoIP] Oslo phone

[Steph Kerman]

Russ Price wrote:
> Steph Kerman wrote:
>> Only electrolytic capacitors are subject to reforming. They do so in 
>> the presence of voltage, not the absence from it.
> It could well be a bipolar electrolytic, and in any case the -48V gets 
> applied to the cap when the phone is on-hook, with the cap passing the 
> AC ring voltage if present.
Ringing capacitors are never electrolytic because their leakage 
characteristics are way too high.  At the time this phone was probably 
made, electrolytics were as a class also very unreliable and not 
considered suitable for general use even in a manned central office let 
alone on a customer's premises.
>>> The cap definitely says 0.5uF on it, and also has a 500V rating.
>> Interesting! That's an unexpectedly high rating. Does it look 
>> original? What does Ralph Meyer say about ringing capacitor voltage
>> ratings?
> *whoosh* Who's Ralph Meyer?
Wrote a popular book that explores the workings of telephones in a 
technical way motivated laymen can understand.  Copies can be purchased 
through the TCI or ATCA with benefit to those clubs.
> Closeup of cap: <http://cnet.fubegra.net/photos/eb-cap.jpg>
Looks like probably original. 500V seems very conservative but no harm 
in that.  I don't think US phones have such high voltage ratings on the 
ringer capacitors.
> The phone's innards: <http://cnet.fubegra.net/photos/eb-guts.jpg>
I see what you mean about the lacing!
> Outside view, with the K1000 accompanying it:
> <http://cnet.fubegra.net/eb-k1000.jpg>
The above link seems to be invalid.
> Closeup of dial: <http://cnet.fubegra.net/photos/eb-dial.jpg>
My 7001 dial has a similar card.  So does my 1960s dolphin gray plastic 
reversible desk/wall model.
>>> Anyway, I was able to let it ring 20 times and not have it trip - 
>>> maybe I won't need to do any surgery on it.
>> It's been my experience that problems that go away mysteriously 
>> return mysteriously too.
> Just like "Heisenbugs" in computer programs!
That's a particularly good example!

SK