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In Reply to: RE: Installing a current meter.. posted by DAK on June 18, 2017 at 16:38:53
I don't think that's an amp meter at all.
I think it's a volt meter being used to calculate amps by ohms law.
voltage divided by resistance is current.
A true amp meter would be connected in series.
Connecting your meter inline, from the bottom of the cathode resistor to ground, should work just fine it what you have is a true amp meter.
Tre'
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Follow Ups:
I would think placing a measuring device in the loop might be a bad idea. Just thinking about it's potential for adding color.. but a calc off a know voltage drop would be less intrusive. ..might be over stating the influence of the added device...
Stuben
"but a calc off a know voltage drop would be less intrusive. ."
That's all a current meter is. A volt meter connected across a known, small value resistor. Something like 1 ohm.
That shouldn't change much of anything as far as the circuit is concerned.
Tre'
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In my case, i am using a 10 0hm resistor to calculate the bias voltage on the power tube of my fixed bias amp. I would then dispense with the resistor and have the meter take its place? Also i have 2 tubes to measure so i can put a switch before the meter to be able to measure both tubes. Dak
Edits: 06/19/17 06/19/17
Make the switching so the meter is out of circuit when not in use.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
So, at first i was thinking of using a dpdt switch with the meter on the center terminal to ground. So, to make the meter offline, i would have to install another switch or what other way can you think of? thanks for the help.
The only thing I can think of right now is 2 SPDT switches. (cathode going straight ground or through the meter to ground)
If both are switches are engaged at the same time the meter would show the total current for both tubes.
Otherwise, just remember to only engage the meter switches one at a time.
I keep thinking there's a way to do this with one switch but I haven't thought of it yet.
Tre'
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Is it possible to configure a rotary switch so that
Off to ground and bypasses the meter
1 to tube 1 current measurement
2 to tube 2 " "
I don't know how rotary switches are configured but i have some.
Yes, it's just a matter of being able to make and break what needs to be.
Break the cathode from ground and connect it to the top of the grounded meter while doing nothing to the other side.
Then re-make that connection from that cathode to ground while breaking the other cathode from ground and connect it to the top of the grounded meter.
Then back to neither cathode being connected to the meter but both are connected to ground.
Doable with the right switch.
I'm liking the 2 switch option but only because it's easy.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
First things first, there's a good chance the meter will have no impact on sonics. Measure it's resistance before going to the trouble of adding a switch. It might be only a few ohms. If it turns out that's not the case, there's no reason to switch it out of circuit when it's not needed. Just leave it in series with the cathode and add a switch in parallel to bypass it to ground. Nothing more is needed.
--------------------------
Buy Chinese. Bury freedom.
power tube current without at least 2 switches, 1 switch for bypass?
For that you'll need a two pole, three position rotary ("L - Off - R"). Contacts should be non-shorting, make-before-break.
--------------------------
Buy Chinese. Bury freedom.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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