Good day,

Working on a repair of an Adventurer for a fellow ham. The TX works however, there is no grid current reading. The meter switch is fine. Measurements of the meter are surprising as well the schematic he forwarded with the Tx. Apparently Johnson went through several updates for the meter movement as well meter multiplication R's.

This meter is NOT a 10 mA FS reading, but 200 mA. The meter Rs is 1 ohm. The meter grid multiplier R is 1k in the unit and per the schematic. However, other schematics show it as 200 ohm. That would be the case for 10 mA FS. And, the plate I multiplier R is 50 ohms per the schematic as well what is in the unit. Again, other schematics indicate 10 ohms. The meter appears original and has the Johnson logo and name. The meter rear plate reads EMICO made in Perkasie, PA. I suspect it is a wind vane meter with the classic boning-boning movement!

So... Did Johnson ever issue a 200 mA FS meter for the Adventurer? And an associated schematic? Looks like I need to change the grid multiplier R to 10 ohms and the plate from 10 to 1 ohm. Otherwise, yes no grid Ig reading and the plate Ip reading is going to be quite wrong.

The line fuse was 5 A, I changed to 2 A fast blow. As well I need to re wire the line and neutral plug in order to help the safety issue! Any information appreciated. Tnx, Alan

Impossible. The basic meter movement cannot be 200 mA. That is the meter FS reading with the external shunt resistor across it. The meter's FS current would have to equal to, or less than, the maximum grid current, which is likely only a few mA.

Hi Peter, thanks for your reply.

Sorry, but this is what was measured. I was surprised. There most likely is an internal shunt.
In any case, with the meter under test ONLY, a series 100 ohm with 20 V source is required to obtain FS reading. Shunting the meter with 1 ohm reduced the FS reading to 1/2. I should add, there are 2-scales on the meter, 0-200 mA and 0-20 mA. I suspect nominal 807 plate Ip is 100 mA while Ig is about 10 mA.

I suspect now that someone has placed an internal shunt in this meter. Although it will read plate current ok, it certainly will not register proper grid current.

Ok, mystery solved and sorry for the occupied bandwidth.

Apparently the owner bought a 200 mA meter and glued the original Johnson decal overlay. Did a nice job, but confused the heck out of me. Now I will chase down getting the proper meter back into the unit.

That makes sense. Glad you got a handle on it.

Shurite made a meter that will drop in perfectly. I'll see if I can dig out the model number.

73, Dean

Great! Thanks.

Alan

Greetings to Alan and the Forum:

If you do not have a copy of the Johnson service bulletin concerning a change to the meter and associated circuitry, I have attached it below.



Regards,

Alan, try to find a Shurite Model 950, stock number 9303, 0-10ma dc. I seem to recall that this meter needed a 1k ohms resistor in the grid position and 50 ohms in the plate position. 73, Dean

The correct meter movement is a 20mA Shurite. Most of the Shurite movements are identical and can be swapped from one style case to another.

The reason so many of these transmitter(as well as Johnson Navigators) have bad meters is because of poor design. Move the plate metering to the cathode circuit and you’ll never have the problem again.

Darrell

Thanks Dean.

The owner is sending me the "original" meter. Which I need to check. The current meter shunts in the Adventurer are in fact 1k and 50 ohms for grid and plate current monitoring. My guess and I may be wrong, is the original meter had a meter R value of 1k. When Johnson upgraded the meter, they went to a 10 mA FS and the multiplier R values went to 200 ohm and 10 ohm. I suspect the original meter therefore was a 1 mA FS. All this guess work is based on getting a half scale meter deflection in monitoring grid and plate currents. I think those current values were 10 mA and 110 mA for a single 807.

It would be nice to see a clear picture of the 2- versions of the original meter(s), what were the scales in use? Anyway, thanks again.

Our posts must have crossed the wires. The 20 mA FS for the original meter makes sense. Yes on the cathode connection vs. in the plate and thank you Darrell!

The Shurite 950/9303 meter that I installed in an Adventurer measured 975 ohms. The printed scale on the meter face is 0-10ma DC. 73, Dean

Great! Thanks again Dean. When I receive the original meter, I will take measurements and tie up any loose ends.

Greetings to Alan and the Forum:

At least you have access to an original meter or its equivalent.... (hopefully). I once resurrected an Adventurer out of another ham's junk box. It was missing both the meter and the band switch. The only schematic I had was in a Johnson catalog. The entire schematic was about 2 inches squared. I had to use an incredibly powerful magnifying lens to read it. Not having the money to replace the meter, I rummaged around in my junk box and came up with a nice D'Arsonval meter that was 0 to 1 mA. I of course had to juggle the shunt values. The only problem (aside from the fact that the meter was way oversize) was that it was labeled "Depth In Feet". As I recall, it went to 250 feet, but it has been a long time. Anyway, my brother used it for his novice transmitter. We worked out that the grid should be 20 feet as I recall and the plate current dip should be at around 110 feet.

If you ever run into an Adventurer equipped with such a meter, let me know... I'd like to buy it back for old times sake.

Have fun!

This may have some interest to you: https://forums.qrz.com/index.php?thread ... ge.637508/
Also the slide switch for the meter has silver contacts and it may get dirty or oxidized and give flaky function, I would put some cleaner or alcohol in the switch and work it to flush out the crud in that instance. Alcohol or contact cleaner that evaporates might be best as there is HV at the switch I think, and any greasy oily stuff in there might create an arc path?

Thanks for the added threads and information!

I received the original meter and the FS deflection is indeed 20 mA. The measured R meter with reasonable accuracy is 400 ohms. This may be a shade low and 1/2 the value quoted for the Shure meter would place it at 480 ohms. Close. Note, the Johnson meter scale is NOT in the meter. It was placed into the new incorrect meter... ugh!

So this old meter would align itself reasonably well with the old meter multipliers of 1 k and 50 ohms. Although those values really are not ideal for getting accurate current readings. I can see why Johnson revised the meter to 10 mA FS.

Now off to see if I can get the RIGHT meter.

Tnx, Alan

Tnx, Alan

Just in case it's useful, here is some information from Shurite c.1955. 73, Dean

Thanks for the Shurite meter info.

I located a nice exact meter and for completeness the 2 meters are now known as follows:

0-20 mA p/n Johnson 484522, the Rmeter ~ 400 ohms

0-10 mA p/n Johnson 484447, the Rmeter ~ 920 ohms

I'll place the meter in the cathode and I think when it
comes time to do work on the Ranger, I'll do the same!
Locating meters that are original is no easy task.

73' Alan