Johnson messenger 223 help

[KC4RAF]

gewecke, your signature

line says it all! lol
"Whatever doesn't kill you...will make you stronger"!

Also in my post, I wrongly stated "cathode screen grid". It should be Control Grid.

 

[KC4RAF]

Darticus, here's info on diodes.

The diodes are: Silicon 75V, 50ma type.
I think you can get a couple of 1N4148 diodes to take their place.
Also, I have come across the manual, (it has the parts list in it). PM me if you want a copy.
Also gewecke, if you need a copy let me know.

 

[darticus]

The two diodes are together right on the center wire of the antenna. Shown
on the far right of the schematic. Disconnected each, one test good and one
test bad. What do you think? I have some 100N1 diodes here but I don't know
if I can replace them with these. I went to Radio and picked up some 276-1620 diodes the seem to cove the 25v 75ma needed as they are 75v 75ma. have my fingers crossed. Thanks Ron
I tested V1= 253V, V2= 254V, V3= 253V, V4= 248V, V10A= 58.7V, 12BW4=
255-281V
Could that little diode cause all the problem? Thanks Ron

If so, it'll give you the type of diodes needed. If not, you'll have to "google" it.
Also check the: the relay working and does it have continuity in both positions?
R50 resistor, good or within tolerance?
Contact points where soldered good?
Cap C1 good?
Coil L1 good?
RF amp tube V1. Can you inject a signal into the cathode screen grid?

HTH.

edit:
be aware that you have some high voltages in that radio. The plate terminal, (number 5 on the RF amp tube) some times run up to 250. Haven't looked at your schematic to see what voltages it carries. Just be forewarned!

350 VAC that'll make you hurt yourself!

 

[KC4RAF]

Ron, yes one diode could, but I think you may

have a cap that could be bad. If you change out the diode, you'r best bet would be to change both, 'cause the good one could be very weak. The voltage listed is 75 volts at 50mA, so you got to be carefull. What you can do is shield your face and eyes when testing, (yes, they can go POP and shapnel flying. But I doubt it at the diffentences in v). Speaking of eyes, believe it or not, you should use eye protection when working of these things. Use a pair of dikes and the litter bitty end you cut off could hit your eye. No big deal, but it does hurt. Also, capacitors, resistors, ICs, etc. can and do explode when too high a voltage or direct shorts occure.
But looking further into that circuit, I would see how that R/T relay acts. (also C1 naturally). Good luck and hope you get it working.

 

[KC4RAF]

Ron, where did you read the voltage

for the rectifier tube, (12BW4). That voltage you posted seems quiet low. At the cathode pin 9, you should be roughly 330 volts.

 

[bigskyradio]

Johnson Messenger 223 help (S meter goes negative)

Unlike your radio Darticus, I have a 223 that does receive fairly well but the S Meter has a problem. I wonder if yours has done this?
With no signal, the S Meter is negative reading after tube warmup. With a strong signal, the meter will read and acts normally. With weaker signals or no signal, it goes fairly hard negative. When powered off, it returns to correct zero position. When powered on, the electrical zero potentimeter on the chassis underside (R9) can be adjusted to affect the level of signal the meter registers but in no case will the meter rest gracefully at zero; it will always peg-negative with little or no received signal. Any ideas? The only schematic I have is so small and blurry, it is hard to follow along.

All 6BJ6 and 12BE7 tubes in receiver chain have been replaced with no difference.
Transmit is excellent with about 4 watts indicated, depending on channel and antenna-SWR curve.
Received signals sound excellent but not quite as sensitive as another Cb (Messenger 4230) on the same antenna.

Anyone with any ideas?

 

[John599nj]

I can't help you with tech advice but that radio was my first cb back in the day. That had synthesize crystals and a great little receiver. I know someone who works on the old tube ham or cb radios in the south jersey area.

 

[KC4RAF]

check your cathode biasing resistor.

I sounds like it may have changed resistance from what it should be. There could be something else at fault, but that'd be the first thing to check.

 

[bigskyradio]

Cathode biasing resistor [ Messenger 223 s meter ]

Sir, you were SPOT on with your recommendation to check the cathode resistor.

I measured the value of the existing resistor on the 12BE6 tube and it indicated just over 3k ohms. Funny because I had already checked the R9 pot which checked out fine but I replaced it anyway since I had a spare of the exact same type and value. I should have checked that fixed resistor even if just to see if the reading matched the color code.

I am kind of working in the dark from a low resolution JPEG copy of a schematic I found online. Under a very good magnifier with added lighting, it looked like the value of the resistor is supposed to be 1.5k ohms which is a match to the color code on this resistor. AH HAH! Obviously schematic and resistor agree and the VTVM disagrees. I clipped that resistor out, rummaged through my resistor drawers and came up with a new 1.5k resistor. Dropped that in place, fired up the radio and bingo! A little adjustment to R9 meter zero, connected an antenna and this old JOHNSON is working perfectly.

High five and thank you so much. Do you know if find the right SAMS Photofact I can buy, if it will have a decent size, clear schematic, suitable for slightly older eyes?

Gene / K7TXO

 

[KC4RAF]

Happy that the info helped you out.

It has been many years since I worked with tube radios/transmitters. But the one thing I remembered most was the biasing resistors caused a lot of problems once they change values.
Yeah, if you can find a Sam's photofact, it will have very readable schematics with all the info needed for that Johnson Messenger. I use to have their website, will try to locate it for you.
Just found it:
http://www.servicesoftware.com/sams.asp
Just click on it and it'll take you to their site! They'll have it for you. (just reinstalled it and it can be a little confusing. you don't need the update download. Photofact # CB-23 is the one you need to ask them for.

 

[bigskyradio]

Roger -
I fine-tuned the S-Meter pot using a signal generator where I could control the input signal level. I have a copy of the JOHNSON Service Guide and I followed that. The result after I connected to an antenna and then compared with two other radios indicated that the indicated db level closely matched the other two rigs. Granted, each one has different sensitivity, selectivity, etc. but the readings were so close between the three, I would say it's just fine. With my wife on the Messenger 223 and I with a handheld out in our forested acreage, the quality of audio and strength of signal was excellent. Early in the day, the long distance signals were strong and heard them very well via a Hex Beam up about 35 feet I had the 223 connected too. No problem communicating to the hand held over the heavy but distant radio traffic while the hand held was set to 1/2 watt transmit mode. So the operation is definitely a success. This and some new panel lights, the old 223 looks and operates great. Thanks again.

Gene

 

[KC4RAF]

Your welcome Gene,

glad I could help. I had to work from memory since I've not been involved with repairs in many, many years. The 223 was a really great radio back in it's days. They had good audio on tx, and receives with beams was out of sight! lol Hope you work a little skip with that piece from the past.

 

[pg11175]

messenger 223

Hi, anyone have a copy of the service manual in pdf form? thanks!!