Telephone Switching > Intercom & Interphone Systems

"FONADEK" for the busy executive in your life...

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gpo706:
Its a handset amplifier, I can only find nice bakelite examples on the net, this is a later plastic one, probably the last of the series before phones came with all the bells and whistles like speakers and hand free operation.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=260750184772&autorefresh=true

Nice wee gadget to play with, though who knows what kind of handset its meant for, I guess a standard 700 series.

Will let you know when I connect a PP9 battery and it doesn't work!

Note also the Royal warrants on it, don't get me started on those frauds, they couldn't even find any reference to my Dictographs in their so-called "archives".

GG:


These types of "telephone amplifiers" were very common through the 1970s, as an affordable alternative to the speakerphones of that era. 

The general principle is that it uses an induction coil next to the receiver to pick up the incoming signal and amplify it via an ordinary transistor amplifier to the loudspeaker.  The handset's transmitter is positioned into an acoustical cavity that attempts to gather up more audio from the person sitting at their desk.  With careful positioning of the main unit and the speaker, you can avoid the feedback from the speaker to the transmitter.  In a quiet room and with you speaking from a couple feet away from the unit, it can be viable as a speakerphone-substitute. 

These units were typically made in Japan and there are variations in the cradle design for different types of handsets depending on the country for which they were intended.  In some cases they don't quite fit.  For example the standard NTT handset from Japan is a bit "wider" than an American G-type handset, and the GPO handset is definitely "longer" than the G-type in the dimension between receiver and transmitter. 

There was also a Dutch version in bakelite, wherein the handset sat atop the unit on a cradle that caused the transmitter and receiver both to face forward toward the person speaking, rather than depending on an acoustical "scoop."  Placing the handset into the cradle depressed a plunger that turned on the unit, and helpfully turned it off when finished, so a forgetful user wouldn't run down their batteries. 

gpo706:
GG - I will have to get back to you when it arrives, I assume the "Royal warrants" applied would infer a UK item suitable for a 700 series handset.

If not I'll have to buy another bloody phone to fit it. LOL!

I reckon the silver knob at the RX end is the on/off button on this unit, when you place the handset on it.

PS those two things at the top end are they "induction coils" they look like the stuff you get when you slide off the diaphragm from a 300 series RX.

GG:


Yes, that thing at the top with the two coils, is an induction coil pickup.  One more thing: it will pick up hum from nearby fluorescent lights and other things that emit AC hum. 

The on-off switch is probably built into the volume control similarly to a transistor radio. 

The "Royal warrants" may or may not indicate that the device was designed to be suitable for a 700 series handset.  Try various handsets until you find one that fist best in the cradle and produces the best audio in both directions, you never know which might work best.   

gpo706:
Came yesterday, didn't have time but to unpack it, weekend off so got to it tonight, it has an "old" style PP9 clip - ie larger than modern PP9 batteries, so off it came and wired through an electrical block terminal to a spare modern PP9 clip-on.

Next a test - held the loudspeaker to the induction coil and voila - audio feedback, so thems both working.

Howlback gets worse as you adjust the volume knob obviously, didn't put it max in case I blew the speaker.

Next I connected my newest bairn, the 8746 ivory to an extension lead to the other side of the room and tried a call, and it works fine, the design has the acoustic scoop for a 700 series handset so it has the lip of the TX resting on the bottom edge of the  scoop.

The volume resistor is a bit crackly when being adjusted at the lower end of the volume but I've found most old mechanical variable resistors are so affected after many a year.

The chrome bit at the top is the on/off button I suspected when you put the RX end of the handset on it.

There is an internal adjuster accessed through a hole below the volume knob, which I have no idea as yet as to what it does, I haven't tweaked with it as yet, I guess another variable resistor for the induction coils?

(DUHHHH - it's wired to the induction coils Scot)!

So works fine, if rather tinny, next I will remove it to another room so I can do a decent test without echo.

The original battery clips are taped into the cavernous battery cavern, so no harm done for a reconvertion to original and they won't get lost.

Anyone have a suggestion for the crackle on the volume resistor, air-spray or maybe a lubricant could make the contacts run better?

Oh yes and the Royal warrants are there, but rather scratched over the years, the left one is HRH the Queen, but right one I can't see the legend under it so will need to decifer the logo.

The superbly grand "FONADEK" logo's are encasuled in clear plastic and subsequently haven't suffered as much as the warrant transfers.

Later...







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