Google+ Antique Telephones & Retro Telephones

Tuesday, July 31, 2012

21A Microphone Replacements

The British 1960's 706 and 1970's/80's 746 telephones were made to last. I believe they were the last UK telephones that were designed so that they could be serviced and maintained for many years, not just replaced and thrown away.

The only weakness of these vintage telephones was the carbon granule microphone (transmitter inset No 16) used inside the telephone mouthpiece. These old carbon granule microphones degraded over time, resulting in crackling and noise that usually gets worse as the telephone conversation goes on. Looking at the photograph below the carbon granule microphone is on the left with a silver top and black base.


BT realised this weakness and started fitting electronic (electret) microphones in the early 1980's. These modern microphones were called "Microphone Insets No 21A". They significantly improved the sound quality experienced by the person at the far end of the telephone call as well as being far more reliable. The red microphone on the right in the picture above is a 21A microphone.

Collectors of old telephones will often pay a premium for these "Transmitter Inset No 21A" so that they can replace the old carbon granule microphones in their vintage 746 telephones, in turn bringing the speech quality up to modern standards, and improving reliability.

Original 21A microphones are hard to find in good condition. Of the few available spare 21A microphones in circulation many have suffered from moisture seeping into the circuitry, which results in a faint hum or buzz during the call which can be very annoying on a long telephone call.

To overcome this shortage of good quality 21A microphones several enterprising British telephone restorers have introduced a brand new equivalent electret microphone.

These new electret microphones were originally designed and made outside of the UK as replacements for the carbon granule microphones used in old American 500 series telephones. These 500 series antique telephones were the American cousins of our British 700 series telephones. However because the American microphones were physically smaller than the UK counterparts these new microphones have been augmented with a British designed and manufactured front/top so that they now fit snugly into 700 series telephones.

The photograph below show the front/top of these new microphones (on the right) as compared with the original 21A microphone on the left.


As you can see from the rear photographs below the new microphone (on the right) has a smaller diameter, however the British manufactured front/top prevents the microphone from rattling around.


The procedure below explains how to fit these replacement microphones using only a small flat bladed screwdriver (takes about 5 mins).


Step 1: Unscrew the mouthpiece cover.


Step 2: Remove the old carbon granule microphone.


Step 3: Unscrew the two microphone terminals and gently remove the two spade connectors.


Step 4: Pull out the metal retaining ring (be careful these are sometimes sharp).


Step 5: Attach the two wire to the modern electret replacement microphone. It does not matter which way round you attach them as they are not polarity sensitive.


Step 6: Fit the new microphone into the mouthpiece as shown in the two photographs below.


Step 7: replace the screw on mouthpiece. Sometimes it is necessary to be firm with the last screw turn as the microphones have a crimp up area to make them a snug fit.





Your vintage/retro telephone should now have as good if not better speech quality than a modern land line telephone.

Tuesday, March 20, 2012

Changing the Microphone in a Bakelite Telephone

Old British Bakelite Telephones such as the 200 series and 300 series telephones used the same handset. This Bakelite handset was known as a model no 164 handset, and was used for over 30 years. It was the standard telephone handset in 1929 and was manufactured all the way through to the early 1960's.



Compared to today’s modern telephone handsets it has a very good ear piece (or receiver). Its only weakness is that the microphone (or transmitter) in the mouthpiece does not live up to today’s expectations of sound quality. This lack of sound quality is only noticeable to the people at the other end of the telephone call. When you are using one of these antique telephones the person at the far end will think you are calling them from the bottom of a well :-) This can be rectified by swapping the old carbon granule microphone out with a modern electronic (electret) microphone. Several makes of replacement electret microphones are available however they must be designed for use in old telephones.

The instructions below show you how this microphone change can be performed.

1) First remove the Bakelite mouthpiece from the handset. If you are unsure how to remove it safely, please see the details on our web page removal of a bakelite mouthpiece.

2) The old Carbon Granule Microphone should just lift out (it is not hard wired).


3) Use a small flat bladed screwdriver to remove the old microphones spring clips (see photographs below).



4 ) Attach two wires to the new electronic microphone ideally red and white wire should be used to make life easier when you fit it (see photograph below). Thankfully new electret microphones used in these vintage telephones are not polarity sensitive, so it does not matter which way round you connect the wires.



5) Connect the new red wire from the microphone to the old red wire inside the mouthpiece, and the new white wire to the old white wire inside the telephone mouthpiece.


6) Modern electronic microphones are smaller than the old carbon granule ones, so you will usually need to cut a small piece of foam to fill the gap to stop the new microphone from rattling around inside the old telephone handset.



7) Finally refit the Bakelite mouthpiece on your handset and test the Bakelite telephone.



Providing the rest of your antique telephone is in good order, the sound quality and usability of your old Bakelite Telephone should be significantly improved.

Tuesday, January 24, 2012

Fitting a 1960's or 1970's Wall Telephone

This is an explanation of how to physically fit, or safely remove British 1960's (model No 711) or 1970's-1980's (model 741) retro wall telephones to a wall.



1) The fist step is to locate and unscrew (half way out) the telephone case retaining screw on the bottom of the telephone. See the pictures below.




2) Next carefully lift the case starting from the bottom of the telephone, as it hinges at the top. This can be tricky if you have not done it before.

TIP: It helps if you hold the switch hooks down and press gently down on the telephone dial while lifting the case from the bottom. See the position of my hands in the diagram below.


3) The wall phone case should now lift completely off. See diagrams of the telephone below.




4) The retaining screw for the separate metal T shaped wall fitting is a single bolt/screw at the bottom, however it is hidden behind where the curly handset cord enters the telephone. So you need to slide the telephone handset cable grommet to the right, as shown below.


5) You should now be able to unscrew the single bolt that holds the T shaped bar to the telephone. As shown below.


6) The telephone is hinged a the top, so simply lift from the bottom as shown above.

7) With the T shaped bar separate fit this to your wall with the appropriate screws for the type of wall it needs to fix onto.


8) Slide the curly handset cable grommet back into its original position.

9) The Telephone can then be hung onto the T bracket at the top, and the retaining bolt tightened at the bottom.


10) Refit the wall telephone case, making sure the cut out in the plastic dial surround ring is in line with the metal finger stop, see below.



Tip: Holding the switch hooks down and pressing on the dial usually makes fitting the case easier.


11) Finally tighten the case retaining screw at the bottom.


12) These instruction should help, either remove these old telephones from the wall or fit them to a new position.

Wednesday, December 24, 2008

Fix for Slow Chrome dials on a Bakelite Telephones

Chrome "type 12" dials used on 200 series and 300 series bakelite telephones can run slow over time. The instructions below explain how to safely take the dial apart to clean/lubricate the governor and gears to fix this problem. You can do this without removing the dial from the bakelite case of the telephone (we have only removed it for clarity of the photographs).


1) Firstly NEVER EVER Spray WD40 or other oil directly into these old dials. The backing to the dial number plate (seen on photographs below) is similar to emulsion paint and is VERY porous. WD40 or other lubricants will soak into this, badly discolouring it and most likely destroying part of the numbers. We see more dials badly damaged by people doing this than any other cause.

2) Using a very small flat bladed screwdriver carefully prise out the metal circlip that holds the paper dial label insert in place (usually covered with a plastic clear label cover).


3) Remove the clear cover and dial lable to expose the centre screw.



4) Next remove the CENTRE screw (and only the centre screw) with a flat bladed screwdriver, and lift it off the chrome finger dial.

5) Carefully remove the larger circlip holding the number plate in position (looks like piano wire). I do this with a compass point, and I think this is the fiddliest part of the procedure.

6) At this point the dial number plate can be lifted out exposing the inner workings of the chrome dial.


7) Notice in the next photograph (below) the back of the dial number plate, which is the porous backing that WD40 or other lubricants will absorb into, and permanently decolour and damage. Be VERY careful not to get any oil near this part.




8) Use a cotton bud to apply (very sparingly) a small amount of watch makers lubricating oil or graphite to the inside of the governor cap (see below).



9) Next use a cotton bud to apply (very sparingly) a small amount of watch makers lubricating oil or graphite to the gear teeth (see picture below).


10) Reassemble the dial in the reverse order.

11) If you have been successful you should be able to dial a “0” and in the time it takes to say (at a steady pace) “one thousand one hundred and one” the dial should return to its rest position.

Thursday, October 09, 2008

Fix for 332 earpiece quite problem




An old GPO engineers maintenance trick for fixing the problem of the earpiece being quite on an early Bakelite 332 telephone is as follows:

1) Unscrew the bakelite earpiece (anticlockwise)









2) Slide the metal diaphragm (thin metal disk) sideways off the earpiece magnets (make a note of which way round it is)





3) Make sure the two screws either side of the magnet are tight.




4) Spray the metal diaphragm (both sides) with a small amount of WD40 and wipe off with a piece of paper kitchen towel.
5) Replace the metal diaphragm (the opposite side up to the way it was removed) by sliding it sideways back onto the magnetic coils.
6) Screw the bakelite earpiece back on.

Then try the telephone again and see if this improves the sound (works about 50% of the time).

Saturday, September 06, 2008

Fix for Slow dial on 746 Telephones

Old 746 telephone dials and 706 telephone dials can run slow over time. The instructions below explain how to clean/lubricate the govener to fix this problem.


1) Place a piece of sticky tape over the clear centre dial cover, and pull if off quickly to remove the clear plastic centre dial cover as in the picture below:



2) Remove the paper label and then unscrew the screw in the centre, to remove the clear plastic (with a flat blade screwdriver).



3) Remove the small wire retaining clip, this is easily removed with your fingers (see below)


4) Lift out the number plate backing (using a piece of sticky tape).


5) The inside of the dial will look very similar to the phograph below. However although the inside parts will be the same shape they will be different colours. Some parts may be plastic others brass.

6) Apply a small amount of watchmaker’s oil onto a cotton bud and use the cotton bud to clean out the governor cap.



7) Move the cotton bud from side to side to get to the complete insides of the cup (see above and below).



8) Replace the Number dial backing (see below).



9) Replace the small wire retaining clip (see below).






10) Replace the clear plastic finger dial and centre screw and tighten the screw (see below).



11) Test the dial rotates OK (to make sure the procedure has worked) and then finally replace the paper label and push fit the plastic centre cover. Then test the dial again.




All should now be OK and you should now repaired on of the UK's nostalgic 746 Telephones.