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Blake Transmitter Information

Started by TelePlay, November 07, 2023, 08:30:56 PM

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The following is what I found about Blake Transmitters in my search for some technical information about the parts of the transmitter. Didn't find that but did find a lot of interesting information that is posted here.

Anyone having additional information can add it to this topic in a reply.

Some of the information in this topic came from Bob's Old Phones which has several pages about the development of the Blake Transmitter from its start in the late 1870's. All quoted text below is from Bob's site.

One of the things I found interesting was the help he got from a Bell employee to make the original transmitter design better: "One problem was a tendency of the diaphragm to resonate harmonically, generating strong overtones causing speech over early models to sound so distinctly strange that it was nicknamed "telephone talk". Edmond Wilson, a Bell employee working with Blake, suggested (and patented) the rubber ring around the diaphragm edge (present on all Blakes we see, although often hardened and broken away with time). Berliner set to , and eventually made two significant improvements. He straightened and strengthened the contact leaf springs (previously curved) and altered the two damping springs to the configuration we know today. He also changed the soft carbon button for "a hard, dense carbon (as) formed in city gas retorts" at very high temperature, because the platinum point of the other contact was eating the button out and ruining the adjustment. Berliner went to great lengths to produce these glass hard carbon buttons, and personally supervised their manufacture, to his specifications, in the Boston Gas Works."

Hence the use or purpose of the rubber washer (O-ring) found on candlestick transmitters manufactured by WE, Kellogg, AE, SC and other companies. The cross section of a Blake Transmitter


shows placement of the "India Rubber Ring" covering the front and back edge of the metal transmitter diaphragm. The above cross section is from Sam Hallas' site, which also has more textual information about the Blake Transmitter.

However, the outside diameter of the Blake Transmitter metal diaphragm is 2.75" which is 0.25" larger than the WE, Kellogg, AE, SC, etc. transmitters diaphragms. As such, the 2.75" Blake diaphragm would use a 2.75" Outside Diameter O-ring having a ring width of 3/8" and a 2.0" Inside Diameter.

The "Blake had a single-contact, variable resistance, carbon microphone. Why it worked better than some over short lines (no single contact could carry much current before pitting or fusing) was due to the (arguably unique) arrangement of the contact points on springs that "floated". The platinum side was always against the Diaphragm - but not attached to it, (as with Edison and others) being on a separate leaf spring, attached to the (moving) cast arm, or bar, as part of an insulated spring pile. The carbon side bore against it, on its own flat spring. The pressure put on the contact itself to keep the points together was supplied by the heavy, short, flat spring joining the cast metal upper arm or bar to the frame. An adjusting screw with a tapered point bearing on the angle of that bar meant the pressure on the contact-pair, pressing against the diaphragm, could be fine tuned infinitely.

This was seen as new and novel by Allsop (1891) because if properly adjusted the system would eliminate the "crashing" of contact-breaking, which spoiled other designs, including carbon pencil types. Lockwood (1882) sums it up: The Blake was a "legitimate offspring of the (Hughes) microphone... the same idea seems to have occurred about the same time to many other minds ...but Blake assisted by several other experts of the Bell Tel. Co. ... was the one to make it work."

To adjust ". . . the Blake transmitter, first, if the instrument is a new one, see that the paper padding is removed from between the carbon block and the frame.

Next slack-back the adjusting screw till the platinum point is just clear of the diaphragm, then turn upwards two full turns. This will usually bring the instrument to the right adjustment. Place the telephone [ie: receiver] to your ear, however, and tap the diaphragm... if all is connected up properly, a sound will be heard in the telephone.

If the sound is dull and short , slack back the screw, but if it is inclined to be prolonged or make a humming noise, the screw must be tightened up a bit.

When properly adjusted a clear musical sound should be heard, but leaving off sharp.

Never at any time turn the screw more than a quarter of a turn at a time, as the best position is easily passed.

If the carbon button should be pulled back, the platinum point should follow it nearly one half inch. In a well-adjusted Blake transmitter, breathing against the diaphragm should be distinctly heard, and in a quiet place, speaking in a whisper or the cawing of rooks (birds) on trees outside should be heard at the other end of the line."

More info can be found on Bob's site.

Also attached are images of the Blake transmitter found in other topics on the forum.


With help from someone who has a Blake, it's been determined that the Blake Transmitter has a 2.75" metal diaphragm.

The width of the rubber ring is 3/8" (same as used in carbon capsule transmitters) which means "India Rubber Ring" has a 2.0" inside diameter.

With these selling for several thousands of dollars (the wood box including the actual transmitter) and being a unique transmitter manufactured in the late 1800s (until replaced by the carbon capsule transmitters), these are rare and knowing someone who has one is just as rare.

This is the original patent drawing for the Blake, which shows the design before it was "improved" by Blake working with WE engineers.