Mystery Transmitter

[AJ1G]

Going through a bunch of old chassis that followed me home from some Hosstraders of many years ago.  Most are either homebrew or ham modified commercial manufacture medium power level power supplies that I bought for the iron on them.

On of them, however, on close inspection is actually what appears to be a complete and  intact commercial manufacture single channel crystal control high HF or low VHF transmitter.  One large (maybe 24 x24 inches) gray painted flat plate chassis that apparently was mounted vertically in a rack within a cabinet,  BC transmitter low level stages style, with the tubes horizontal facing the front, and the exposed under-chassis facing the rear.

Most tubes are missing, but it has ceramic sockets for  a crystal, a 6L6 oscillator/possible multiplier?, 6L6 multiplier/driver, single 807 final.  The RF coils for the stages look like that its output frequency is probably up in the 30 to 50 Mc region.

Has a few small metal octal tubes that appear to be a speech amp, and a 5U4 rectifier.  I initially thought it might be an FM transmitter, but there are a pair of leads with plate caps next to a single socket labelled RK60 going to what looks like a pretty hefty mod transformer, so maybe its an AM transmitter?

Has a lot of all Kenyon iron, and an open frame relay which appears to be used for antenna T/R switching located near the final tank circuit.  Also has a large multi-pin Jones receptacle apparently for audio input and control circuitry.

Anyone know what this might be?  No nameplates other than those on the Kenyon iron. Appears to be late 40s early 50s vintage.

[Pete, WA2CWA]

A picture might help in the ID.

[AJ1G]

Just realized I misread the RK tube number, it's an RK60, which is a full wave rectifier with two plate caps on the top of the envelope.  So the associated transformer must fbe or the HV of the single 807 final.  Most likely is in fact an FM transmitter, unless there was a separate modulator on another chassis. Will try to add some pictures. An awful lot of iron for something in the 25 to 30 watt output class! 

[AJ1G]

Spent a little more time looking at the mystery beast.  It is AM, found two more 6L6 sockets in line with a hefty mod transformer and the 807 final on the opposite side of the mod iron.  Bringing it up to Nearfest for people to puzzle over.  Would make a nice low power HF rig with the appropriate coils and caps.

[AJ1G]

A picture might help in the ID.

Here it is.  Picture courtesy of KD3HT.

The audio chain is a 6SJ7 apparently driving a pair of 6C5s in PP transformer coupled to a pair of 6L6s in PP

[WA2SQQ]

Maybe an early voice paging transmitter? I recall voice paging just above 10M, identifying as "This is KEA860 Pageboy, New York"

[W2PFY]

I thought it was an early 42-50 mhz exciter for the old FM band but now that I see it has a mod transformer, it was probably early aircraft AM ground based transmitter since cops and fire departments used FM in most of their early stuff? Looks like a coil for the old five meter band.

[AJ1G]

I was also thinking VHF AM aircraft ground station transmitter, but was skeptical because of the 807 final.  However, I came across some 807 specs that stated it is capable of operation up to around 125 Mc with a 55% de-rating factor.  So maybe aircraft band.  The coil does look appropriate for that band.  Maybe Wilcox?  Bendix?

[W2PFY]

Well it looks like there are too many turns on that coil to be very high in freq?

Is there an underside pic available? I am not sure how many clues that will give us but there may be something microscopic that can be discovered?

[W3RSW]

32 MHz out, PI net. C14 plate tune, C15 load a/c the rotor is grounded to chassis.
Last use, 27 MHz, bwaa, ha ha !

[KD6VXI]

Maybe so, maybe not.  The original 11 meter Cb band did include 5 channels which did allow for 25 watts (input I believe)...  And the use of amplifiers. 

The Courier BL-110 is a type accepted linear for class D CB.

Maybe it helps?

--Shane
KD6VXI

[W3RSW]

Interesting .  It does look like all the channels, if selectable, have to be fairly adjacent since final tune and load are 'set and forget.'

[KD6VXI]

There where 5 channels set aside.  The CBers called them A or alphas.

26.995
27.045
27.095
27.145 (iirc)
27.195

Still AM. 

Also, maybe related.  CB DOES allow for one way voice  paging.

So, if it has 5 crystal slots, maybe this helps?

--Shane
KD6VXI

[W2PFY]

Yes I remember the paging signals on that mystery CB frequency.

It sounded like BeeBooBaabooobeeeebaaboobababooie 

[WA2SQQ]

Yes I remember the paging signals on that mystery CB frequency.

It sounded like BeeBooBaabooobeeeebaaboobababooie 

Paging? Really? So you just answered a question I've had for probably 40 years. I live in Bergen County (NJ) and in this area CH 23, 27.255 had a constant S9+20 signal belching out those tones. We were told that it was used to control the traffic signals. Never knew where it came from, but it was there 24 x7 x 365. Turned on my Lafayette HB-444/25A, but today CH23 is rather quiet.

[KD6VXI]

The tones should have been on one of the alpha channels.

Standard Cb, as I (mis) interpreted the rules only allowed for voice.

Radio shack sold voice pagers based on Cb radio tech.  Each one had a sel call style tone burst, but the actual information was speech.

Traffic lights.....  :-)  oh gosh, some of the 'theories' us kids came up with in San Diego about what we heard....

--Shane
KD6VXI

[Pete, WA2CWA]

Back in the late 50's through the 60's, diathermy machines used frequencies around 27.255 MHz. If you were within range, you heard tones and occasional howls.

[W2PFY]

Paging? Really? So you just answered a question I've had for probably 40 years.

I remember asking someone what the tones were and the answer I received that is was a paging system from hospitals to page doctors? Even though that was the answer, I didn't know till very much later what a paging system was? I was just a dumb plow boy farmer in those days at age 15. I wish I could go back to being 15 again

Pete, I never heard the diathermy on the CB band around 1957. I think they were outlawed for home use not too long before the fifties? My grandfather had one for his wife and he gave it to me at some point. I tore it apart to make a CB amp with it. The FCC dictated that your crystals had to be .005 within the channel and one of my friend got a citation from the FCC for being off frequency on channel 11. In the late sixties a doctor treated me for shoulder problem with an identical machine that I received from my grandfather.They are still used in medicine but they must be a better machine now with shielding and filtering? The reason I was given for them being outlawed was that they were wiping out TV sets since, most people received TV over the air. 

[KA0HCP]

Ultrasound devices have been used for muscular treatment since at least the late 1970's. Also trans-dermal electrical stimulation devices.  No annoying RF!

[AJ1G]

When I get a chance I am going to see where the 3 apparent 6L6>6L6>807 plate tuning circuits resonate at with either a GDO or by injecting manually swept RF into them with my URM-25D and observing the output on my recently acquired at NEARFEST Tek 422 scope.  By the  number of turns on the  coils for the three stages they obviously  are multiplying up to some where in the vicinity of 30  MHz plus. 

If you take a look at the upper left corner of the chassis the large 5 pin socket is the crystal socket.  Kind of an odd socket for a crystal.  Doesn't seem like there was more than one crystal there.  Been looking around at old Wilcox and Bendix AM aircraft radio links and have not come across  anything like this chassis.

Is there a way you can do an Internet search where you can post an image and do a search on it for matches similar to a word search?

[W2PFY]

If you take a look at the upper left corner of the chassis the large 5 pin socket is the crystal socket.  Kind of an odd socket for a crystal.

I have seen those tube sockets quite often in old commercial transmitters. It must have been a way to cut costs for a 2 pin special crystal socket? Just punch another hole for a tube and wala, a crystal socket

[KD6VXI]

Is there a way you can do an Internet search where you can post an image and do a search on it for matches similar to a word search?

http://HTTPS://images.google.com/

--Shane
KD6VXI

(edited to correct a ; to a : in the URL)

[AJ1G]

Thanks for that link Shane.  Had to replace the semi-colon with a colon to get it to work.  Very useful search method!  Just had to select the camera icon, and then paste in the url for the image posted here on this thread.  Didn't find any thing close yet, but returned all sorts of cool radio and electronics images though . Great way to get lost for several hours or more exploring!

Going down that paging transmitter search path, found out that the original paging transmitter was invented by none other than Irving Gross, a pretty well known ham inventor who also developed the Joan/Eleanor communications system used in WWII.  His original VHF paging system was built in 1939 by Reevesound in NYC, and used at NY Jewish Hospital.  1939 seems to be a good match to the apparent vintage of Mystery Transmitter based on its appearance.  No luck on searching on Reevesound though for anything further on paging systems.  They were apparently a very well known recording studio company supporting the record and film industry in the 30s through 50s.

[WA2SQQ]

Back in the late 50's through the 60's, diathermy machines used frequencies around 27.255 MHz. If you were within range, you heard tones and occasional howls.

OK, so all those "good buddies" may not have been crazy! Thanks for sharing.

[KD6VXI]

Bah!  Sorry for mangling the link.

One of the benefits of touch typing on a keyboard a third the size of your fingers with zero tactile feedback!

I'll go back and edit my original for people coming after the fact.

--Shane
KD6VXI