newbie post: making your own subset

[michael_recchione]

Hi everyone,

I'm new here and new to collecting phones, though I've worked in the telecom industry for over 27 years, and have always been fascinated with Bell System stuff.

I've run across candlesticks and other old phones from time to time, but much less frequently run into ones with subsets (or subsets by themselves).  I'm familiar with the idea of using another old phone, like a 500, as a parts donor for a subset (or using all of its innards as a subset).  My questions now have to do with making a subset, or more accurately, a subset of a subset without cannibalizing another phone.

To use a candlestick as an extension phone that doesn't originate calls or ring, I'm assuming all you really need is a hybrid network and a way to go off/on-hook.  Is that correct?  Is anyone aware of specs/plans available, either for the (classic) passive hybrid networks using coils, or a more modern active equivalent using resistors and ICs?

Thanks in advance,
- Mike

[HarrySmith]

Welcometo the forum. Be warned, "phonitis" is a progressive, incurable disease
Get out now!
Kidding aside, I  have no idea about building your own networks but subsets are fairly plentiful and usually fairly cheap. I have used a bellbox, adding coil and condensor from a 302. Also a 302 base will make a good subset and one of our members makes a nice cover for it. Broken 302's are not hard to find. I have also installed a 425 network from a 500 into a wood wall phone. Mini networks installed in a candlestick are a popular way to do it. They come up on eBay a lot.

[davidbholcomb]

I've run across candlesticks and other old phones from time to time, but much less frequently run into ones with subsets (or subsets by themselves). 

See http://www.classicrotaryphones.com/forum/index.php?topic=7848.msg86320#msg86320
for why that is. Welcome to the forum, this place is full of great material.

[michael_recchione]

I've found schematics for passive hybrid networks, both sidetone and sidetone-suppressing, but none of the ones I've run into give values for the inductors or capacitors used. 

I'd like to take a crack at building the hybrid, even maybe winding the coils myself.  Does anyone know where I could find the actual specs, i.e. not just parts numbers or wiring diagrams?  If I can get this to work, I will post the solution here. 

Thanks again,
- Mike

[dsk]

Hi & welcome.

Yes you can!
Winding an induction coil is not an accurate hobby, and the result may wary a bit.
To really make it from the bottom, you will need some steal wires to make the core, the wires used in flower-shops to make the flowers keep their right position is perfect. Cut them in suitable equal  length. 4 inch? Make to wooden blocks to make ends 1.5x1 inch and drilling a hole Ø=3/8" in each.
Fill up with core material. Wrap the core with 1 layer of thin paper.

Reading for windings: Use some painted copper wire, as thin as you may handle with ease.
3 sets of windings 1400, 700, 1400 turns. This will make approx windings like the coil in a WE 302.
You will get a usable, but considerable less effective transformer than the one used in the 302. The impedance's will be a little random, but not to bad. Follow the wiring diagram for a 302, or a subset using the same induction coil. The value of the capacitor is not critical but should be at least 1 microfarad rated 200V or more, about 5 would be good. I'm not 100 % sure of the winding directions, But I believe you start at terminal L1 (Named as the coil in 302) next is R Next coil starts at GN and ends at R, the last one starts at GN and ends at C.  The mid winding (700 turns) may need a resistor in series to reach an ohmic value at at least 40 ohms. (Actually testing various resistors to make you hear yourselves as weak as possible will tune the anti sidetone to an optimum.)

I have done this just once, when I was a teenager, and don't remember well all the details. I baked the coil into gypsum?

dsk

[michael_recchione]

Hi & welcome.

Yes you can!
Winding an induction coil is not an accurate hobby, and the result may wary a bit.
To really make it from the bottom, you will need some steal wires to make the core, the wires used in flower-shops to make the flowers keep their right position is perfect. Cut them in suitable equal  length. 4 inch? Make to wooden blocks to make ends 1.5x1 inch and drilling a hole Ø=3/8" in each.
Fill up with core material. Wrap the core with 1 layer of thin paper.

Reading for windings: Use some painted copper wire, as thin as you may handle with ease.
3 sets of windings 1400, 700, 1400 turns. This will make approx windings like the coil in a WE 302.
You will get a usable, but considerable less effective transformer than the one used in the 302. The impedance's will be a little random, but not to bad. Follow the wiring diagram for a 302, or a subset using the same induction coil. The value of the capacitor is not critical but should be at least 1 microfarad rated 200V or more, about 5 would be good. I'm not 100 % sure of the winding directions, But I believe you start at terminal L1 (Named as the coil in 302) next is R Next coil starts at GN and ends at R, the last one starts at GN and ends at C.  The mid winding (700 turns) may need a resistor in series to reach an ohmic value at at least 40 ohms.

I have done this just once, when I was a teenager, and don't remember well all the details. I baked the coil into gypsum?

dsk

Thanks!  That's exactly the information I was looking for.  Is the impedance on the 4-wire side at all critical? 

[dsk]

Not very critical, at list not at this level. If you want high quality sound, you have to do lots of fine tuning depending on the impedance of your receiver, transmitter, and line.  You will get a 1920ies quality, but still usable.

It is funny to make it once, but you are saving lots of work, and costs, and getting better quality by stealing components from professionally made telephones.

I just made my coil to a LB telephone, and it worked to the neighbors, just 2-300 yds away.

dsk

[michael_recchione]

It is funny to make it once, but you are saving lots of work, and costs, and getting better quality by stealing components from professionally made telephones.

I get that.  But I hate to cannibalize something that's working.  And, based on some limited poking around, dedicated subsets run over $100.  Maybe I just haven't been looking in the right places...

I'm pretty sure I've got some old phone parts in a box somewhere - maybe I'll find what I want there. 

Thanks for the help!
- Mike

[dsk]

I love experimenting, a simple subset could be a ringer and capacitor + a capacitor 1-5 uF and a coil with some high resistance for voice signals, but still not more than 100 ohms dc. A relay will due.


This will be a sidetone circuit, but it is the simplest well working subset ever made. (Kellogg)

dsk

[dsk]

Some more research, and I located this diagram.
This is an Antwerp telephone.
Winding ratios are  added on the diagram.
If you ignore the hookswitch and the way of using the capacitor for both ringer and voice circuit, it is identical to the W.E. 302.
The induction coil terminal 1= L1, 2=R, 4=GN and 3=C
The direction on the turns are reverse at the coil 4-3
Winding 1-2 starts at 1, 2-3 at 2 and 4-3 at 3!

For Western electric coil no: 101A The winding ratios will be:
1-2 1 (at 22 ohms)
2-3 0.38 (at 75 ohms)
4-3 0.7 (at 19ohms)

The winding 2 3 could be made with higher resistance wire than copper, or just put in series with a resistor.
(Using a resistor will make it more easy to match the impedance)

dsk