Automatic Electric Type 80 Desk Sets

[MMikeJBenN27]

What is that screw that can be clocked to 0, 1, 2, 3, or 4 in the base plate of Automatic Electric Type 80 desk phones for?

[tubaman]

From this thread - http://www.classicrotaryphones.com/forum/index.php?topic=10292.0
"The potentiometer/rheostat on the bottom is for the adjustment for side-tone and transmitter current. It won't hurt for you to adjust it. Remember it is not desirable to adjust it to hear your own voice loudly."

[Jack Ryan]

What is that screw that can be clocked to 0, 1, 2, 3, or 4 in the base plate of Automatic Electric Type 80 desk phones for?

It is a manual adjustment for line length compensation. In later models, automatic line length compensation was used.

Without line length compensation, subscribers close to the exchange create a very strong transmitted signal. This not only creates a loud sidetone, it is loud for the other subscriber. The other subscriber then speaks more softly and the first can't hear him so he speaks more loudly. And so it goes on.

Manual compensation was cheaper and generally only had to be adjusted once. There was a problem though with some PABXs - if the phone was adjusted for communication between extensions, there was often a problem when speaking on an outside line. The PABX was close, the CO was far.

Early WE 500s and all GPO 700 series telephones used a positive temperature coefficient thermistor (a lamp) in their auto compensation circuits. Subscribers using these early phones were afraid the phone was going to burst into flames because the lamp glowed. This was particularly eerie with a red phone.

Regards
Jack

[TelePlay]

As an FYI, glad I posted this fix some time ago for reference, I took that circuit out to improve the frequency ringer strength. This "removal" was done without damage so it can be reversed.

If your phone has a straight line ringer, this might not do anything with respect to the ringer strength.

http://www.classicrotaryphones.com/forum/index.php?topic=23704.0

[Jack Ryan]

As an FYI, glad I posted this fix some time ago for reference, I took that circuit out to improve the frequency ringer strength. This "removal" was done without damage so it can be reversed.

If your phone has a straight line ringer, this might not do anything with respect to the ringer strength.

http://www.classicrotaryphones.com/forum/index.php?topic=23704.0

I don't see how it does anything with a frequency ringer. The compensation circuit is disconnected when the phone is on hook.

Circuit attached - AE 80 on hook. (sorry it's a but grubby)

Jack

[TelePlay]

I don't see how it does anything with a frequency ringer. The compensation circuit is disconnected when the phone is on hook.

Don't know. Had a phone with a faint ring. Trial and error thinking. With the circuit as shown in my topic, with how the rheostat was removed, the ringer improved to the volume of a C4A ringer set to low volume.

Removal of the circuit did not affect the talk circuit volumes on either phone.

Can't guarantee that will work with any other similar phone. I was glad to get that frequency ringer to work on a 20 Hz ring voltage.

Surprised me it worked but gave me a working phone without finding a straight line ringer. It was a unique make-do non-destructive hobbyist's solution to a specific problem.

[MMikeJBenN27]

Thanks folks.  Now one of life's great mysteries has been solved!

[TelePlay]

I don't see how it does anything with a frequency ringer. The compensation circuit is disconnected when the phone is on hook.

Having a few hours trying to remember "why" I thought it made a difference was this. From the wiring and circuit diagrams that was inside the phone,



and the left side annotated with balancing circuit in yellow and ring circuit in red is attached below.

This circuit shows that while, yes, the talk circuit is not completed when on hook, L2 (yellow) feeds through the rheostat and is split by the rheostat with some of L2 connected to terminal 2 and some to terminal 14. Terminal 2 leads to a resistor (R) and terminal 14 leads to a resistor/capacitor (RC) in parallel.

The red circuit is the ringer on hook. The yellow circuit (while not completed) is hanging on one side of the ringer circuit.

By taking the rheostat out (putting in the blue bypass straps), that feeds L2 directly to Terminal 2 and Terminal 14 (equal input to the R and RC components?), I guessed that the R and RC components had an affect on the ring "frequency" to move it from 20 Hz downward a bit toward 16.6 Hz, the one third harmonic of the 50 Hz ringer. Those R and RC components may have had an effect that decreased the ring frequency seen by the ringer a bit to make the 50Hz ringer work better.

It was reproducible. Take the straps off and wire the rheostat back in and it didn't ring. Disconnect the rheostat and put in the straps and it rang like a 500 on low volume.

I don't know. Maybe one of the long time, 30 year experienced members who have restored phones forever or any member who has an electrical background and understands "frequency" and what affects it can provide a "sounds good" or "you're crazy" reply to my experimentation and guesses.

All I know about frequency is that it can't be measured easily in a complex circuit. The searching I've done on trying to do that all said one needs an oscilloscope, decade resistance box and a variable frequency sine wave generator. Maybe I'm wrong with that too and if someone knows how to measure frequency in a complex circuit easily, please post the component set up and measuring method.

[Jack Ryan]

Having a few hours trying to remember "why" I thought it made a difference was this. From the wiring and circuit diagrams that was inside the phone,

Yes, my response contained an edited version of the same circuit.

and the left side annotated with balancing circuit in yellow and ring circuit in red is attached below.

This circuit shows that while, yes, the talk circuit is not completed when on hook, L2 (yellow) feeds through the rheostat and is split by the rheostat with some of L2 connected to terminal 2 and some to terminal 14. Terminal 2 leads to a resistor (R) and terminal 14 leads to a resistor/capacitor (RC) in parallel.

The red circuit is the ringer on hook. The yellow circuit (while not completed) is hanging on one side of the ringer circuit.

Unless a section of circuit is completed, no current will flow and no voltage will drop irrespective of the frequency. The compensation circuit is attached at one end but has no effect.

By taking the rheostat out (putting in the blue bypass straps), that feeds L2 directly to Terminal 2 and Terminal 14 (equal input to the R and RC components?), I guessed that the R and RC components had an affect on the ring "frequency" to move it from 20 Hz downward a bit toward 16.6 Hz, the one third harmonic of the 50 Hz ringer. Those R and RC components may have had an effect that decreased the ring frequency seen by the ringer a bit to make the 50Hz ringer work better.

It was reproducible. Take the straps off and wire the rheostat back in and it didn't ring. Disconnect the rheostat and put in the straps and it rang like a 500 on low volume.

If there was a reproducible effect, I would guess that there was some other, unnoticed problem with that particular telephone. Perhaps an unseen short or perhaps the hook switch failed to disconnect part or all of the compensation circuit.

I don't know. Maybe one of the long time, 30 year experienced members who have restored phones forever or any member who has an electrical background and understands "frequency" and what affects it can provide a "sounds good" or "you're crazy" reply to my experimentation and guesses.

All I know about frequency is that it can't be measured easily in a complex circuit. The searching I've done on trying to do that all said one needs an oscilloscope, decade resistance box and a variable frequency sine wave generator. Maybe I'm wrong with that too and if someone knows how to measure frequency in a complex circuit easily, please post the component set up and measuring method.

I've never had a job fixing phones but I have been an electrical (electronics) engineer for a long time. Of course, I am not infallible, but I do have some understanding. I am sure that the effect you observed was real, I just don't think it was caused by the compensation circuit as designed.

Regards
Jack

[TelePlay]

I've never had a job fixing phones but I have been an electrical (electronics) engineer for a long time. Of course, I am not infallible, but I do have some understanding. I am sure that the effect you observed was real, I just don't think it was caused by the compensation circuit as designed.

Thanks. And, yes, a completed circuit should a have no affect. I didn't trace out or check out all connections and contacts in the phone because once the straps were in place and the phone rang, I thought I was done. I suppose there are several possible circuit completing pathways after the R and RC components, as you said, a dial or hook switch short of sorts.

I have no idea why a 50 Hz ringer would work on a 20Hz ring voltage. I guess I just posted that "fix" in case anyone else ever had a 50 Hz ringer in a phone with a balancing rheostat and wanted to sell if a few connection changes would make the ringer stronger.

I don't have the phone anymore, it went to a knew home for a bargain price thru eBay. Leich phones made by AE don't hold the value of WE stuff.

Thanks for the knowledgeable conversation.

[Jack Ryan]

Thanks. And, yes, a completed circuit should a have no affect. I didn't trace out or check out all connections and contacts in the phone because once the straps were in place and the phone rang, I thought I was done. I suppose there are several possible circuit completing pathways after the R and RC components, as you said, a dial or hook switch short of sorts.

I have no idea why a 50 Hz ringer would work on a 20Hz ring voltage. I guess I just posted that "fix" in case anyone else ever had a 50 Hz ringer in a phone with a balancing rheostat and wanted to sell if a few connection changes would make the ringer stronger.

I don't have the phone anymore, it went to a knew home for a bargain price thru eBay. Leich phones made by AE don't hold the value of WE stuff.

Thanks for the knowledgeable conversation.

You're welcome.

Regards
Jack