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Hi all.

I'm working on getting this JV2 back to factory. Not a restoration just functioning. And I'm a rookie so its quite the learning curve.

I have a lot of chaos with the voltages on this unit and one item I am stumped on is the R57 shunt > picture + schematic attached.
Why would the voltage be the same on both sides? Unless then repealed Ohms law I should have a lower voltage on one end?

Its a 5.1 Ohm that measures about 6.1 and I get 3mV across it power on. DC Voltage is -67? on both sides with T2 or T1&T2 on.

What am I missing? Can I replace it with a 5 Ohm 2 Watt and be fine ?

Name/Callsign?

see below . . .

On Thu, 23 Feb 2023 11:37:29 -0800, "Iowa59 Ham" <iowa59ham@...> wrote:

I have a lot of chaos with the voltages on this unit and one item I am stumped on is the R57 shunt > picture + schematic attached.
Why would the voltage be the same on both sides? Unless then repealed Ohms law I should have a lower voltage on one end?

Its a 5.1 Ohm that measures about 6.1 and I get 3mV across it power on. DC Voltage is -67 on both sides with T2 or T1&T2 on.

What type of meter are you using?

If it doesn't have a high input impedance, it might be loading the circuit
slightly on the other end of the resistor. The older Radio Shack meters had a
low input impedance compared to most of today's or the old vacuum tube meters.

Or you might not be noticing a decimal value difference on a reading. If you
measure a voltage drop across it, then a meter should see that difference
between the two measurement points to ground, also. One reading should be either
-66.007 or -67.003 volts, but I wonder if your meter will let you see such small
differences. (Unless you mean -67 mV.)

The 3 mV difference means that current is flowing and the resistor isn't shorted
somehow internally. What's the current you measure? Does it agree with the 3 mV
drop and resistor value you measure with one leg disconnected?

That's where I'd start.


Donald KX8K



----------------------------------------------------
Some ham radio groups you may be interested in:
/g/ICOM /g/Ham-Antennas
/g/HamRadioHelp /g/Baofeng
/g/CHIRP

Thanks Don.

Yeah I have a Craftsman dmm and a new Astro AI.? I elected to cut out and measure the shunt and it tested good then using clip leads I inserted a 5ohm resister but got the same results.

Then just out of curiosity I placed the Dim bulb tester in line and brought the unit up on LV and I have the 200 V light bulb on when the variac hits 20 volts. So something is shorting to chassis is my guess. I removed the tubes but no change. The T1 thru T4 transformers ohm out close to spec so no reason to suspect those are causing the issues.
So Im on a hunting expedition.

73
Patrick/ W0KKM

I hate those!!!

I hope you stumble across what's wrong. There's an EF Johnson mailing list. It
isn't very active, much like this list, but it's another place to see if you can
get help. More information here:



Click on directory of lists and find the one for Johnson, and fill in your
information.


Donald KX8K




On Wed, 08 Mar 2023 14:24:07 -0800, "Iowa59 Ham" <iowa59ham@...> wrote:

So Im on a hunting expedition.

----------------------------------------------------
Some ham radio groups you may be interested in:
/g/ICOM /g/Ham-Antennas
/g/HamRadioHelp /g/Baofeng
/g/CHIRP