Antbody know the correct method of measuring CB off hook loop current?

[RB]

Yes, I agree.
I like to keep things original too...
However...I seldom have that chance.
as with this project, I do not have a schematic, or even a list of components
used it the original installation. So I am making this up as I go lol!
Please excuse my ignorance, but I have trouble seeing circuits in motion.
Could you explain the function of this extra cap in the circuit?
I know it will block the DC, so that should help with the 2 lines interacting
with each other, and maybe stop the current changes, or maybe smooth the transaction?
While allowing the voice to pass...Is there anything else I am missing?
Thanks for your wisdom here!!! I feel I learn something from everything you comment on!

[dsk]

No, that is it, it separates the 2 DC paths, but lets the sound pass.  That amy reduce the high differences in current, It will still be differences, but hopefully within the limit of what the phone maker did designe the phone for.

When I look in alder catloques some phones are made for up to 60 mA, even when we know that most phones should have 18-30 mA for their best transmitting whitout frying the carbon transmitter.

[RB]

Ok, I am with you.
I have seen from 50+mA, down to about 5mA depending on how I connect each piece together.
If I can cut about 20mA, "and keep it out", It may be good enough to move forward.
I will try to install the cap tonight, or tomorrow nite.
Gettin kind of excited about having this thing working!
Wil post more when I have some more results to talk about.

[RB]

Update # 2
I am happy to add...
The Result of the 2 cap mod applied to the circuit,
brought the overall current down from the Low 40's, to the low 30's. "Happy Dance!".
The Facts:
The caps are 2.5uf, that's what I had.
The inline resistor, "present in Ext 1 only",  had to be 620 ohms. This did not seem to change from Ext 1 to Ext 2...
This puzzles me. Seeing the Relays used to supply 48v, are either 670 ohms, Ext 1. Or 700 ohms, Ext 2... But, I am not complainin!
Question:
If the Resistance of the supply coils has little effect on the overall Current of the circuit,
What effect would increasing/decreasing the coils value have on the overall circuit?
Ooh, This is gettin fun!!!

[dsk]

Nice to hear that my idea helped. 2.5 uF will probably work fine, 2 in series gives 1.25 and that will still let reasonable voice signal go trough the circuit.

The DC resistance of the coil has some effect, (ohms law) but the impedance or resistance for voice signal is of great importance together with a reasonable sensitivity for off hook identification.  Probably will how it is affected by ringing frequency also be of some importance.
This is a little out of my comfort zone to act as one who knows....

[RB]

It has good voice between the 2 phones.
I realized that the coil resistance difference is only 30 ohms, may be too small to see on the meter.
it took around 100 ohms to make the needle move much. "about 2mA".
This setup has no ring voltage. the extensions cannot dial out, "no dial tone supplied yet. only signal the desire to the switchboard.
The board has to be coupled to my big switchboard. That one can dial out.
I lost power to the Op set by doing this mod. "Op power came in through the extensions". Will need to restore that somehow.
Then it is on to the Coupling of the two switchboards!
The big board has an isolation transformer to couple my LB phones with my omi.
I may be able to use the input for the CB phones also???
Gettin closer!!!

[RB]

Update 2 or 3...whatever. This is good!
Well, I could say I am happy,
But that is an understatement!
I installed the 620 ohm Resistors tonite, one on each extension. and I am happy to say
I am hovering right at 31mA on both extensions. "Big $#it eatin grin"
My 2 extensions are solid now! TYJ!
On to Ext 3.
It will connect this board to my big Switchboard, via an isolation transformer.
I guess, I will need to replicate the power input from Ext 1 and 2, to make this one Hot.
That should restore my Op transmitter, and get me to the isolation transformer.
Runnin out of room in the Relay cabinet, lol.
Hope I don't need to enlarge it...AGAIN! lol.
The extra parts mounted nicely on the dual rj11 socket.
It would be great if I could find parts small enough to hide inside the dual box!
Movin forward.

[AT2796]

I came across this table today. You're probably past this already but it can't hurt to share.

[RB]

The next update.
We are cruising rite along.
I got me a set of three phones willin to play nice together.
Ext 1, 2, n 3 play nice together at 30ma.
My third ext went to 30mA after I swapped the 220 ohm for a 125 ohm.
It was workin fine.
Then, I installed the iso transformer, and the current went to 40mA.
Probably shuda left the 220 will see.
The phone on ext 3 can hear, but not speak..yet.
I suspect the circuit will ultimately satisfy the  input  of the 616.
I have all 3 Red lites working, and 1 & 2 of the White.
Beer