CM30-50 Transmitter Progress

[Steve - WB3HUZ]

Only if the 125% modulation causes the PEP to exceed 1500 watts.  ;-)

So, those of us that can muster up 125% pos peaks are in whyolation???
oh My Gawd......will the FECES catch me??/
Fred

[Opcom]

oops - -I did not see the posys where you decided to keep it. Good!!

Well at that rate, I'll never get on 160 from my current QTH.

A 60x120 lot doesn't lend itself to anything decent for a 160M antenna, the 75 Meter is about all I can get I guess...


And if 50 watts isn't enough to do it, well.. I'll guess I'll look at moving it on.. it was free.. free is usually "You get what you pay for".

Thanks for the replies

well, if you don't want it... I think it's pretty interesting.

[W5EFR]

Thanks for the offer...

I am going to try and put it on 75 meters... I have enough room in teh lot, and I already have a 75 meter dipole up.. the Apex is at about 25'... better than nothing...


If i decide to sell it, I will sell it to Mr. Martin, he would really like it as a working example of Mr Cunningham's work, and they would be built for Missionary service.

[W9RAN]

Hey Bow,

Welcome to the Cunningham Owners Club!  I'm betting you and I may be the only members but at least you're not alone ;-)

I have one just like that, or at least very similar with the solid state modulator.  It actually works pretty well, considering the fact that I would never hook it up to my 160 meter dipole and run full power and go driving around in my car just to see how far it transmits, or anything like that!

Drop me a PM and I'll get you a copy of the manual.    I had heard that Mr. Cunningham passed away, as you can see from his website I'm sure he's modulating from a better place now ;-)

73 Bob W9RAN

[W5EFR]

Thanks for the reply Bob!

You have a PM.

Is your unit as scary looking as mine underneath? 

[W5EFR]

UPDATE!

Thanks to Bob's (W9RAN) Hard work and efforts of scanning, I now have a Manual for this thing!

THANKS BOB!

Reading the Manual, it is actually rated for 36 watts, but can push 50 watts with out 100% modulation.

Here is the Schematic:

http://riley-music.com/BowsStuff/CM3050/14CunninghamSchematic.jpg

Tuning information for the AMBX Band:

http://riley-music.com/BowsStuff/CM3050/18CunninghamTuneUpChart.jpg

And Bottom Layout Drawing:

http://riley-music.com/BowsStuff/CM3050/20CunninghamWiringDiagram.jpg

Any suggestion to get this thing on 75 meters, or possibly 40 meters... or both?

[WD5JKO]

Looking at that LPB Antenna tuner in the first post shows that this was a carrier current setup that injected RF into the 3 phase power of a large building. This type of AM broadcast was common in the 1970's, and would fill a building of RF, mixed with multiples of TV horizontal oscillators. The reception usually was poor. The balanced system usually could barely be heard 100 yards away from the building.

I used to work at WFRS in Michigan where I maintained 17 Carrier current transmitters located in college dormitory boiler rooms. The LPB (low Power Broadcast) company was well represented at this college along with some home brew transmitters.

Jim
WD5JKO

[W5EFR]

Actually, this was pulled from a transmitter shack where it was a backup for a Broadcast station in Brookshire, TX, when they upgraded.

I saw a date on a drawing in the manual for 1992, so it isn't that old...

[w4bfs]

printed and looked over schizmatic ... looks like L2 is not too critical and may work as is ...L3 looks to be resonated with cap in 6DQ5 grid and will need to be reduced roughly to 1/4 for 80 mtr ....could look at most any working low power xmtr and get an idee ... reduce L5,6 about the same ....put in variables for C12,13 ... the grid dip osc is your friend here ...BEFORE changing anything verify resonance for buffer and final plate at assigned freq and then ease them on up ....mucho fun ...73...John

[KD6VXI]

Actually, this was pulled from a transmitter shack where it was a backup for a Broadcast station in Brookshire, TX, when they upgraded.

I saw a date on a drawing in the manual for 1992, so it isn't that old...

MAN,

I used to live in the Waller area...  Bought a car from someone in Brookshire.

Wish I coulda landed that TX... Looks to be somethin cool.

--Shane

[k4kyv]

There used to be a lot of little broadcast transmitters like that in Canada.  The stations were unmanned using a phone line audio feed to relay CBC to small isolated communities.  I remember seeing several of the antennas in Nova Scotia years ago.  Typically a 150' or so (total length) inverted L held up with 40' or so wooden utility poles, with the call letters of the station printed on a sign attached to the building.

I talked to a ham in NS last winter on AM and this topic came up.  He said that those little relay transmitters have about all been taken out of service now.  He told me he had one of the transmitters he was considering putting it on 160m.  It uses a single 6146 in the final.  About the same power output as a Ranger.

[W5EFR]

Well.... I have finally got some time to look at this thing with the schematic... and this critter ain't right.

My first clue was the 540V on the plates.. when it is supposed to be 450V (as per the schematic after the half wave rectifier) out of the transformer.

It seems the power transformer was changed out from the original. The schematic calls out a 300ma transformer, this is a 750V 175ma transformer.

hmmm...

Then I see the extra diodes and resisters that were not in the schematic, so it has been hacked pretty good... so I need to find a 450V 300ma power transformer for starters...

Any suggestions?

[w4bfs]

450 V @ .3A ....maybe an old TV .... they are still heading to the landfills ... my wife sez I can not adopt any more orphans or recycles .... the 6dq5 is probably ok at the higher voltage just remember the rated plate dissipation ( uh 18 W as I recollect) probably good for a bit more ...73 ...John

[K1JJ]

peak envelope power (of a radio transmitter) [PEP, pX, PX]: The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle at the crest of the modulation envelope taken under normal operating conditions.
-- Federal Standard 1037
Pretty simple stuff.

"Under normal operating conditions"

Interpretation:   If operating conditions AIN'T normal - like when Cooter and Bubba try to take over the channel - then you can you run whatever PEP (munky swing) you want.

T

[W5EFR]

450 V @ .3A ....maybe an old TV .... they are still heading to the landfills ... my wife sez I can not adopt any more orphans or recycles .... the 6dq5 is probably ok at the higher voltage just remember the rated plate dissipation ( uh 18 W as I recollect) probably good for a bit more ...73 ...John

Thanks John...

I'm a looking for a Transformer better rated for this thing...

Hell, a 12BY7, 6V6GT and a 6DQ5... I wonder what I can get away with for ma rating...

[W5EFR]

I have a major update on my transmitter restoration project.

I ended up rebuilding the power supply circuit on the Transmitter back to stock, and only used 1/2 of the installed power transformer secondary windings. The put my B+ Voltage level down to a more manageable level, and reinstate the previously bypassed Neg Voltage Bias supply. this allowed the power level control to actually control the carrier from 0-50 watts,  and I was actually able to modulate it using the "internal" modulation circuit (TIP100).

It got about 60-70% modulated before the circuit started to clip, squaring off the positive peak of the envelope,  but I am a lot further than I have been with it in the few years I've had it.

Now once I get the modulation circuit figured out, I'll have to find a empty frequency, locate a crystal for that freq, and build a leaky Coax.... 

[W5EFR]

I am happy to report:

I have Carrier:


I have Modulation:


This was done with an 8 watt mono amplifier feeding the External modulation connection (through the modulation transformer) with a 1kHz sine wave, into a dummy load.

Now that I know it will modulated properly, I can work on the internal modulation circuit more.

I'm not sure how it sounds "On-Air", but it looks pretty good...