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Author Topic: 10 meter AM - From a Johnson Messenger Two?  (Read 10023 times)
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Bow/KD5KZN
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« on: January 23, 2007, 09:26:16 AM »

Hello all.

I am thinking about getting on AM, as soon as I upgrade to General.

I have a Icom IC-718 already, but I would like to get on AM with tubes and I recently picked up a Johnson Messenger Two CB... It was free, how could I say no? It still has the mic attached and I only need to find the power plug for the back.

I was thinking about converting it to 10 meters, if I can still find some crystals, but I was wondering if there are any other modifications I could perform during the clean up to make it sound and operate  better on the air.

I have never worked with tube radios before, but I have built several tube amps and such, so I know how to not get fried.  Shocked

Any Suggestions for a new guy?

Thanks

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KL7OF
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« Reply #1 on: January 23, 2007, 10:34:22 AM »

I have several of these old Johnson 11 meter rigs.  There are two styles....early and late...Black face and chrome face....IIRC, johnson made a 10 meter model as well.  Shouldn't be any problem to raise the freq up to 29000 khz.  a crystal change and some tx and rx tweaking.. I've not looked inside the rigs or the manual...I plan to fix one up for 10 meters, but it won't be this winter..

 Get a schematic  and and have at it......It would seem like a great rig to learn from ....
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Bow/KD5KZN
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« Reply #2 on: January 23, 2007, 11:05:42 AM »

Thanks,

Mine is a Black Face (I should have stated that in the first post). I found a schematic here:
http://www.cbtricks.com/radios/ef_johnson/messenger_2/graphics/messenger_2_sch.jpg

In a tube guitar amp, I can change the frequency responce by altering the values of the bypass caps between the gain stages, or off the bypass caps on the cathodes. I would venture to guess that I can do the same here?

Any suggestion for values to start with?

I was wondering, what type of modulation does this thing use?

The power amp is a a 7091 tube running Class C, according to the service manual. The Schematic says it should run with 360V on the plates for 2.8 watts of output. Is there any way to increase the power out?

Thanks and sorry for the new-guy questions.
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WB3JOK
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« Reply #3 on: January 23, 2007, 11:06:19 AM »

I also have a couple of CB's (including one that does SSB too Grin)
and would like to put them on 10m.

Is there a "channel plan" (fixed frequencies) for crystal-controlled units on 10m?
-Charles
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WBear2GCR
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« Reply #4 on: January 23, 2007, 11:17:18 AM »

Ummm...

 Grin

            _-_-bear
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Pete, WA2CWA
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« Reply #5 on: January 23, 2007, 12:55:20 PM »

Since we are at roughly sunspot minimum, most of the AM activity, if there is any, generally is around 29.01. However, as we climb the cycle, AM activity can spread from 29.0 all the way to 29.2. At this point, 2.8 watts, unless you're using an antenna with some gain, is generally not going to get you very far. With some of these rigs where you have to install crystals, crystal receive does not allow you to be flexible to monitor and work the wide AM 10 meter band range unless you buy several receive crystals, several transmit crystals, etc. A CB with tunable receive, or one that covers all 23 or 40 channels, would at least give you the flexibility to monitor band activity. A modified SSB CB rig would at least give you some db advantage in working stations but not on AM. 73 Magazine had a series of articles back in the 70's on the modification of a variety of CB rigs.
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WD8BIL
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« Reply #6 on: January 23, 2007, 01:10:04 PM »

Find someone in your area that does mods for the CBers. They use 10 meters a lot.

Steve is right, find some crystals or build a vfo and do some tweeking.
My 1st 10 meter AM stuff was done with a Cobra 19XL. Once the crystals were re-arranged the unit tuned up to 29000 with no mods at all.
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KB2WIG
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« Reply #7 on: January 23, 2007, 01:24:09 PM »

" I was wondering, what type of modulation does this thing use. "   Looks like plate modulation...  the screen grid gets tickled with a little audio also.

It looks like you wont get much more PWR out of that tube. But, if ya want to play with it, use the Johnson as a driver.  maybe a 807 or 811 lin yeer  might be fun.. you cud overbuild it with parts for a real maul, and when you get bored with it, the parts go into something like a Tesla 300 (see amwindow link).

Pete is right.....   but, you may be able to rig up a vfo/vxo for it. Something like a "learning experience"....  

FYI, the 7061 is also known as a 12AB5

   gud luck     klc
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WB3JOK
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« Reply #8 on: January 23, 2007, 01:24:39 PM »

Find someone in your area that does mods for the CBers. They use 10 meters a lot.
I wouldn't want to work freebanders if they're not legally licensed... nor encourage more of them by supporting their "techs"...  Roll Eyes

Quote
Steve is right, find some crystals or build a vfo and do some tweeking.
My 1st 10 meter AM stuff was done with a Cobra 19XL. Once the crystals were re-arranged the unit tuned up to 29000 with no mods at all.

That's what I'm planning (crystals) - it'd almost be easier to start from scratch if I were going to build a 10m AM transmitter with a VFO! Besides, with a tunable receiver, if my transmitter is still fixed-frequency, then I can hear them but not work them anyway...
That is why I asked... what frequencies are commonly used?

The recommendation for 29.010 MHz sounds like a good starting point. Maybe I could relocate Ch.1 to 28.500 or 29.000 and go up by the original increments (10/20 KHz steps). One of the junkbox CB's is a synthesized Lafayetter "Telsat SSB--75", IIRC. I agree 2.8W isn't much!

Unfortunately I got rid of my 73 Magazine collection back in the late 80's  Cry

-Charles

ps 'BIL, love the .sig quote. Who said it?
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KA7WOC
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« Reply #9 on: January 23, 2007, 01:54:32 PM »

I picked up such a modified rig several years ago.  Got it from Al (IEY) at a swap.  It came with matching cb footwarmer.  Xtals too.  I pretty much worked where ever the band was open to.  Cross continent no problem when the band was in. 
Overall tho it was awkward to use.  I sold it off a couple years back.  No regrets. 
Go for it.
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Bob (aka Boatyard)
Bow/KD5KZN
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« Reply #10 on: January 23, 2007, 02:37:19 PM »

" I was wondering, what type of modulation does this thing use. "   Looks like plate modulation...  the screen grid gets tickled with a little audio also.

It looks like you wont get much more PWR out of that tube. But, if ya want to play with it, use the Johnson as a driver.  maybe a 807 or 811 lin yeer  might be fun.. you cud overbuild it with parts for a real maul, and when you get bored with it, the parts go into something like a Tesla 300 (see amwindow link).

Pete is right.....   but, you may be able to rig up a vfo/vxo for it. Something like a "learning experience".... 

FYI, the 7061 is also known as a 12AB5

   gud luck     klc

Thanks KLC.

Yup, I'm not looking for a monster, mainly a learning experence.

Like Charles(WD8BIL), I just want to give it a shot and see how it does.

There isn't a CB "tech" around here that I would throw money at. I do all my own stuff, because I can't learn if I'm paying somebody to hack up my equipment.

I just figure that this Messenger would be a little more entertaining to get up and running than the Knight T-60 I have...
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WD8BIL
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« Reply #11 on: January 24, 2007, 09:33:42 AM »

It was a joke guyz  ! Roll Eyes
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w5rkl
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« Reply #12 on: January 24, 2007, 09:20:21 PM »

The original Johnson "White Face" (Chrome face) was a 12 watt crystal control radio on 28.5Mhz. This was before
11 meters became the "Citizen Band".
 
These radios can be made to operate on 10 meters by substituting the crystals on both receive and transmit. Each
oscillators will have to adjusted to oscillate on the new 10 meter frequency. The final output will have to be
adjusted to resonate on the 10 meter frequency you are considering putting it on.

For 11 meter CB operation, the power output was reduced to 5 watts input by using a dropping resistor to the final
amplifier plate supply. Wiring around this resistor will increase the power output to 10 watts. Also, replacing the rectifier
tube with solid state diodes will give an additional 2 watts. I ran one of these back in my CB days. The final tube will
run much hotter when bypassing the resistor.

I would look into finding a better radio that is already set up for AM mode. You don't have to spend a fortune to
get on AM. Listen around on 75 meters, 3875 to 3890, to hear what the variety of gear people are using on AM
these days.

73's
Mike
W5RKL


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Bow/KD5KZN
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« Reply #13 on: January 25, 2007, 12:38:15 PM »

Thanks Mike,

I just wanted to play with this radio, since it is already in my inventory.

See what I can make it do and how good I can make it sound.

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Ed KB1HVS
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« Reply #14 on: January 25, 2007, 03:37:10 PM »

I have one also. Messenger 1) It was my dads. I use to get on it when I was a kid. I too would like to put it on ten.
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KB1HVS. Your Hi Value Station
K9FH
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« Reply #15 on: January 25, 2007, 11:01:05 PM »

Some of the early tube type CBs were single conversion receivers with a 1650 kc I.F. frequency. If they injected on the high side, the receive xtals were in the 10 meter band. With this arrangement, the receive crystals could often be placed in the transmit positions and then get the transmitter circuits tuned up in the ten meter band.  Surprisingly, quite often the receiver would work with low side injection by using the CB transmit xtals in the receive positions. Whether it works depends how much adjustment you have with tuned circuits of the receiver and transmitter. Quite a few models would tune right up on 10 meters with just a swapping of xtals positions.

Example: 27.255 mHz + 1.650 mHz=28.905 mHz

Early Phase Locked Loop CB's had a generic PLL chip where you could change the frequency divider ratio by grounding or pulling up to Vcc a couple of pins on the PLL chip and then do a re-alignment. 
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W2JBL
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« Reply #16 on: January 26, 2007, 12:19:56 AM »

     those early Johnson Messenger rigs work OKfine on 10. you obviously need to realalign the whole thing to work there, but i did quite a few of them, and they worked well. hifi audio was not part of the program though. the commercial versions came in a few different bandsplits, like 25-28, 30-35, etc. back when i first started in the biz the guy i worked for was an EFJ two way dealer. he sold a lot of those things, and they held up very well. i had two fleets of Checker taxis running them on 35.040 (AM). one day my boss handed me a 25-28 radio to put on that freq. it didn't make it! i had to order various caps and coils to change it over, and eventually i got it going. 10 watts out going down hill with a tail wind. a local highway department ran a fleet of them on (yes they were licensed) 27.430 up into the 80's.
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Bow/KD5KZN
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« Reply #17 on: January 26, 2007, 03:36:29 PM »

  hifi audio was not part of the program though.

But do you think one could be modified for it?
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W2JBL
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« Reply #18 on: January 28, 2007, 09:19:29 PM »

i never tried to modify one for HIFI audio. i did a few Lafayette tube CB's for it and got them sound OK though. all the Johnson stuff i worked on was in Checker Taxis.
Amos and the Fresh Air Taxi compnay were not worried about fidelity. with a bit of work most any tube transmitter can be made to sound pretty good.
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Bow/KD5KZN
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« Reply #19 on: February 02, 2007, 04:05:22 PM »

Well, I got it fired up today.. and it works...

The only downside so far is that the modulation is only about 70%, judging from eyeball measurment on an O'scope...

I guess I'll start by tweaking that...
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N8LGU
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« Reply #20 on: February 13, 2007, 03:22:57 PM »

    Welcome to the AM Frat, Bow! You are inspired the same way most of us were we we got started. Learn by asking and tinkering. That is what distinguishes us ( a very unique group) from the appliance operators. Before you know it, you'll be on the air with your own scrotus maximus homebrew maul. Life is too short for plastic radios.
    Congrats on the General, also!
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"Rock Cave Dave"
Bow/KD5KZN
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« Reply #21 on: March 14, 2007, 02:10:34 PM »

Thanks Dave!

I am still looking for crystals for my Messenger 2...

And I need to get rid of the banana mic that is hardwired so I can install something with a bit more audio bandwidth... Smiley
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AF4K
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« Reply #22 on: April 19, 2012, 08:41:39 AM »

I have those Johnson Messenger crystals available at:
http://af4k.com/crystals.htm

Regards - Bry, AF4K


W5EFR writes:

"I am still looking for crystals for my Messenger 2..."
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gerry_w1id
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« Reply #23 on: April 19, 2012, 10:57:46 AM »

The Johnson Messenger I, II & 223 all use transformer coupled plate modulation. Most tube-type rigs in those days used Heising plate modulation. One thing to consider is they are all 455kHz single conversion so you will have to choose your receive crystals so that you minimize images. Those rigs also use industrial tubes intended for mobile service with so-called dark heaters so if you should try and replace some of them it could turn out to be an expensive proposition. However, you can get away with just plain equivalent receiving type tubes without any noticable degradation in performance. Johnson also had a line of low band VHF rigs which were virtually identical to the CB models so outside of crystal selection, you should have no problem whatsoever putting your Johnson rig on 10 meters. I mentioned the 223 because it was a repackaging of the II. It used the same chassis with the same holes punched out but mounted sideways in a case. It used a mixer type synthesizer using germanium transistors to cover 23 channels which worked quite well.
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w5rkl
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« Reply #24 on: April 19, 2012, 07:48:14 PM »

I mentioned the 223 because it was a repackaging of the II. It used the same chassis with the same holes punched out but mounted sideways in a case. It used a mixer type synthesizer using germanium transistors to cover 23 channels which worked quite well.

I have a Messenger 223 operating VFO control on the AM segment of 10 meters, 29.0Mhz and above.

http://www.qrz.com/db/w5rkl

The small cabinet (HD-1410 keyer) holds the VFO, digital display, universal amplifier, and 8VDC regulated supply (amplifier operates from 8VDC). Main power is provided by a regulated 12VDC color camera brick that plugs into the rear of the VFO. VFO signal and VFO control sockets (2 female RCA) provide connections to the 223. The rear chassis has 2 RCA sockets, one labeled VFO C (control) and one labeled VFO S (signal). I added a DPDT relay that performs 3 functions

1. Routes the VFO signal between the receive mixer transformer L3 and transmit driver transformer L5
2. Controls the VFO signal shift up 455Khz in transmit and down 455Khz in receive
3. Control speaker audio, on in receive and off in transmit (microphone is not required to be plugged into the mic socket)

Relay power is rectified 12VAC through a half wave rectifier then controlled by pin 5 on the microphone socket and wiring in the D-104 microphone base. Power output is 5 watts. I've worked into Washington state with good audio report.

I also have 2 Messenger One's on 29.0Mhz crystal control operating at 7 watts output.

Operating low power on 10 meters is a challenge but also a lot of fun.

73s
Mike
W5RKL
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