Purpose of Tube in WE501?

[Slal]

Hi everyone,

Answer is probably bound to be here, but maybe search terms are too vague.

A little background though.

At phone gallery, WEBellSystemChristian was kind enough to compliment a 501 I'd added.  Posted that all it needeed was its vacuum tube.

What?  A telephone needs a tube?  Thought those were for old amps & receivers.

RotarDad helped me out with an eBay link to the missing part.  So now the 501 has its tube.

What was the purpose of the tube though?  It acted as a kind of switch?  Were they ever able to prevent users from 'listening in' to others' conversations, or is that a myth out of old movies.

Thanks for reading

--Bruce

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Phone humor & a little fun.  Clearly I have nothing better to do at the moment...  Moderator can edit/remove if wasting server space.  : )

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Help!  I can't figure out why I'm not getting any sound out of the right hand side of the speaker (phone) jack.  Wires from the 4 prong thing are hooked up to the 1/4" jack, and I can hear music out of the left side, but not the right.  If I didn't know better, I'd swear the right hand side looks like some kind of micro - phone!
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[TelePlay]

Some call them "cold cathode tubes" and here is an interesting a very old topic that discusses them with what was known back then.

     http://www.classicrotaryphones.com/forum/index.php?topic=111.msg710#msg710

This is a more recent post with a more technical slant

     http://www.classicrotaryphones.com/forum/index.php?topic=12416.0

and another that may help you figure out the "why."

     http://www.classicrotaryphones.com/forum/index.php?topic=2669.msg36682#msg36682

Use the forum search with the two words "tube  diode" and you will get a lot of hits.

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Edit: last of the 3 links updated to post the one that should have been there, instead of the second link twice.

[AL_as_needed]

Having a WE 501 (with the tube reinstalled), this is in  short what I have come to know from CRPF and other sources.

-The 501s were specifically made for party lines, where there could be up to four subscribers on a single line. The tube allowed for a wider range of selective ringing options to  be used by the TELCO to maximize service on a small infrastructure. (While Teleplay's links are more detailed) Depending on how the 501 was wired into the party line, it would "ignore" the ring signal from the CO, allowing one of the other four phones on the same line to ring by itself.

This idea was quickly phased out as service improved and party lines were replaced with a more extensive single subscriber network, as well as improvements made to the 500 series internal network. Could be wrong, but I believe by the 60s party lines were limited to two subscribers and the remaining 501s were rewired to act as regular 500 C/D sets.  Finding one now with the original tube still in place is a rarity,  but NOS tubes are still out there. 

[Slal]

Having a WE 501 (with the tube reinstalled), this is in  short what I have come to know from CRPF and other sources.

-The 501s were specifically made for party lines, where there could be up to four subscribers on a single line. The tube allowed for a wider range of selective ringing options to  be used by the TELCO to maximize service on a small infrastructure. (While Teleplay's links are more detailed) Depending on how the 501 was wired into the party line, it would "ignore" the ring signal from the CO, allowing one of the other four phones on the same line to ring by itself.

This idea was quickly phased out as service improved and party lines were replaced with a more extensive single subscriber network, as well as improvements made to the 500 series internal network. Could be wrong, but I believe by the 60s party lines were limited to two subscribers and the remaining 501s were rewired to act as regular 500 C/D sets.  Finding one now with the original tube still in place is a rarity,  but NOS tubes are still out there.

That's a good summary, and from the other links understand *why* four subscribers.   Mine was probably rewired or has extra springs in dial?  Haven't looked.  Every once in a while will come across a dial with a bunch of shunt springs.  "SAT" springs are correct term?  Am kind of rusty since don't stop by here often enough.  : )

@ Teleplay

Thanks for the links.    Don't think I've had the privilege of meeting Bill, but he seems to know his stuff.  2+2 = 4  Even I can figure that out!

Unbeldi really good at the diagrams.

Will have to read Jorge's abbreviated diagram more closely.  Phones & old amps obviously not the same when it comes to schematics. 

Looks like I've benefited from others hard work though.  I just put the tube and phone worked. Never a thought how you guys figured it out.

best

--Bruce

[RotarDad]

Bruce -  Looks great with the tube back in there!   The dial is not different in a 501,  only the tube was needed and specific configuration of the ringer wires.   I think the latest 501 I've seen is a 7-61 - saw it on Etsy a few years ago and saved a pic.  60s versions are uncommon I believe.  I really like 501s - they have more "early communication" history to them imho.  Paul

[Babybearjs]

  Its funny to read this.... I have a 306 that has a tube in it and it works OK on the line, though the ring is too soft... wound up disconnecting it and wiring it as a 302 (bell part only) I left the tube in the set for historical reasons... showing that the tube used to be the "Capacitor" of the bell... wonder how many phones that are still wired for "PL" (partyline) service are being used as a regular phone... and those 426 tubes are hard to find.... I had one, wound up loosing it in a move sometime back... 

[AL_as_needed]

Slal: Usually 501s that were put into single subscriber use are simply rewired on the network block and the tube removed by the phone tech servicing the unit at the time. Any WE 500 set can be wired to act as a basic C/D set if need be, even key sets.

I think the tubes also had a mild radio active element used in them (KR-85 specifically). Never checked my NOS (2-73) tube with a meter but the box warns of improper disposal etc.

There are pictures somewhere of how to rewire the tube into the phone and still have it ring on standard line ring-voltage. I could always open mine up and send you a few detail pictures if you'd like.

Babybearjs: did your 306 have an actual vacuum tube, or a more modern resistor? My 302 and 5302 came as a box of parts and in that box was 250v, 1.0K resistor. Wired both as standard C/D sets as I was new to the 300 series of phone at the time.