EE-8-B Telephone Supply Voltage ?

Edwards Finance > Phones

Q. this is an odd one. I've just finished repairing an old EE-8-B field telephone (WWII) that I purchased recently. I want to hook it up to the telephone line and use it as an answer only extension. The question: the EE-8-B was designed for 3V operation, but modern telephone equipment is 5V. Thus, when I speak into the receiver of the EE-8-B, the other party hears a very soft voice. IS IT OK to run the EE-8-B at 4.5 to 5 VDC, beyond its rated voltage? Ckt diagrams for the (essentially identical) EE-8-A are linked below.

A. I would believe that the problem is not the voltage. It would be the impedance, providing the earpiece in your unit is in good working order. I don't know your particular unit, but I would think the problem is the impedance match. There were many communications equipment from that era that were using 200 to 300 ohms instead of 600 to 900 ohms as per modern day telephone equipment. This would lower the sound you hear by about 6 Db. That to the ear would be a significant loss. The schematic is typical of the many magneto field phones used around the world irrespective of the maker. I assume that you want to connect it to your current POTS line and use it to answer incoming calls, is this correct? I would recommend against doing this since the line loading factor of such a telephone may drastically affect the operation of other normal auto telephones. It is intended mainly for use on long private lines not associated with the automatic network. The automatic network runs at a nominal 48V but due to the impedance distribution of the line, the instrument and the line interface circuit in the exchange, only around 6V appears across the telephone when the line is looped. The characteristics of the field phone will not be ideal for a modern POTS line and the transmitted level to line may well be quite low and hardly audible at the other end. Your field phone may work in some fashion however you must still use a 3V dry battery to power the transmitter. The transmitter inserts in these phones are generally of the carbon granule type and if you push too much current through the transmitter by upping the voltage then you run the risk of "frying". This is the term used to describe to hash or noise generated in the carbon microphone due to excessive current which produces arcing between granules and the subsequent production a fine grit of carbon powder which generates scratchiness on the line. Modern (and old) telephone equipment is current limited with an open circuit voltage of 48V. If you draw less than the usual 20 to 40 mA, then the voltage will climb, all the way up to 48v, or more like 54V when the CO has light load during off hours. Great info...thanks, folks. The off-hook impedance of the EE-8-B is about 100 ohm, a bit less than is typical for today. That said, installing 2 brand new D cells (providing 3.22 VDC total) and doing the tapping trick with the old carbon mic, I can speak into my equipment and be heard sufficiently on the other end of the line. At some future point I may rig up an external 4.5 or 6 V or so supply so that I don't eat up batteries. I suspect that with less then brand new batteries the volume at the other end will fall off drastically.

Ask Edwards a Finance Question

Other Questions:

Alternative to Bellsouth for business phone service?

Does anybody know if there is a company that provides local business phone service in Atlanta aside from Bellsouth? Did business phone service get deregulated and opened up to competition as well as residential?Media One (now called AT&T Br...

Is the 11c classified as a hybrid? Lucent sales says that it is but I cannot substantiate the claim. The line between digital PBX and hybrid PBX is a bit of a blur to me. Any comments would be appreciated.Lucent Sales has the Nortel product line ...

Im hoping that someone could help me with a little question I have. I'm looking to set up IP phones at 12 sites that are already connected to a fibre network. The phones shall only be use internally to call from one station to another and there...

I am writing to you out of necessity because of a situation that has become frustrating in the hiring process in your system. I truly feel I am being overlooked for an employment opportunity because of a conviction that was over seven years ago...

Do you use Tracfone or any other prepay cell phone service as your primary telephone? Do you not have a regular landline phone in your home? I am considering disconnecting my landline, I currently have a prepay phone service as well in which I...

Edwards Finance Menu

Ask a Question
About Us / Me
Contact Me
Privacy Policy

Sitemap

My Favorite Sites

PFBlog
Google Finance
Yahoo Finance
Motley Fool
Nveille's Financial Blog
AllFinanceMatters
Free Money Finance
2MillionBlog
The Terror Finance blog

Q&A Subjects