634 AT Subset

[djtownsend]

I see this subset on ebay.  It is a 634 AT subset and have never heard of this model of subset.  There is a picture below and see a tube unit on top of the ringer.  Can anyone inform me of what makes this type of subset unique and what that device above the ringer is?  The seller has no idea.

Thanks for the info.

Dan

[Phonesrfun]

It is designed for party-line selective ringing.  If memory serves me, I believe it will work with a straight line ringer and provide for up to 6 individual parties to each be rung off the same line without affecting the others.

The cold cathode tube is at the heart of the ability for it to decipher the ringing.  Without the tube, you have three possibilities for ringing.  Bridged across L1 and L2; or from L1 to ground; or from L2 to ground.

The cold cathode tube allows for doubling that capacity by superimposing a biased voltage over each of those three to achieve 6.  The tube senses whether the biased voltage is positive or negative.

This method of ringing has not been in use for years.

Depending on the condition of the tube, it is possible to wire it for straight ringing that will work on today's systems.  If the tube is bad, a simple .5mF capacitor can be used to have it work.

[paul-f]

You can read BSPs covering the 634-type subsets in the TCI Library by searching for 634, or browsing the BSPs starting with 502-200. 

There's also a 634AT wiring diagram showing the connections of the tube for several scenarious and a list of telephones it was primarily used with.

http://www.telephonecollectors.info/index.php?searchword=502-200-401&ordering=&searchphrase=all&Itemid=1&option=com_search

[djtownsend]

Thanks for the info everyone. 

Can I use this subset as just a normal 634 subset and not utilize the multiple line functioinality?  I assume so and can even remove the tube component.  I have no need for this functionality but do need the functionality of a regular 634 subset.

Dan

[paul-f]

It should certainly be possible.  We've certainly seen countless 501 sets with similar tubes that had been converted to 500 sets by removing the tube.

If I were doing it, I'd check wiring diagrams for other 634 subsets without the tube to see if there are any differences, and use them as a wiring model.

It would be nice to make the change in a manner that is reversible and save any removed parts with the subset, so that it can be restored to original condition if we find some day that there aren't many examples of 634AT left.

[Sargeguy]

I have a 634AT that I converted.  It uses two condensers in addition to the coil.  I just took out all the wiring and put in a condenser and coil from a 302. 

[Doug Rose]

I have a 634AT that I converted.  It uses two condensers in addition to the coil.  I just took out all the wiring and put in a condenser and coil from a 302. 

Sargeguy....by doing that, doesn't it ruin the the original piece? I sure think it does. There is no turning back once you have removed everything. Or drilled holes etc. Isn't it better in its original beauty? A piece of history?  Just my opinion, but why not just use a 302 base. Its a ready made subset? You told me that parts from two like phones of the same maker, makes a Frankenphone, which I totally disagree with. What has this 684AT become? Not trying to cause trouble, but I  know I probably am; I just don't get the logic in destroying history. I have collected phones for over 30 years and never seen one. Never! Sorry....just my humble opinion. I thought we were in the business of trying to preserve history, not alter it. Yes, I'd rather keep an original phone with all dates matching and have it not working than replace the receiver element and make it work. Only when everything is perfect, a specimen.  Resale is one thing, but history is another. I apologize in advance, but this is just wrong. Again, just my opinion.....Doug

[Sargeguy]

I had not realized it was such a rare gem.  Don't worry though, all the parts are in a box somewhere in my phone room, so I can reverse the process if I ever choose to do so.

[bingster]

Party line subsets with tubes (like the AT variant) show up rather frequently on ebay.  They're not as scarce as one might think. 

Just a few opinions...

Like some others, I don't necessarily think the term "franken-whatever" is a pejorative term.  It's just a quick-cute way of saying it's not as it once was.  Nothing wrong with a frankenphone or a frankensubset in my book. 

Regarding historical originality, I think it's a laudable cause to preserve something that's largely or completely original.  But in the past, if equipment showed signs of trouble, the Bell System would replace a defective part practically instantly.  The Bell System is gone now, so I gladly replace any defective part in the name of the System, because it's what they would have done.  UNLESS... it's a terribly rare telephone, which ALSO happens to be completely date-matching. But that would probably be my only exception.

[djtownsend]

Does anyone have a picture of a 302 subset showing how it is wired?  I'm really interested in creating one of these subsets?

[Wallphone]

There is a diagram in the Subscriber's Set section of the TCI Library that Ray K. did that shows how to use a WE 302 as a subset.  < http://tinyurl.com/6g8kjr9 >
Doug Pav