|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
67.189.207.135
In Reply to: RE: multimeter is reading very high plate current posted by banpuku on February 20, 2017 at 11:44:50
There is no way you can pass 100ma though a 22K resistor so there is either something wrong with your meter or your hookup procedure. (were you bypassing the 22K resistor when you did this test?)
all you need to do to meadure the plate current is measure the DC voltage across the 22K resistor at idle then use ohms law. In your schematic you have 322V B+ and 106V on the plate so that is 216V across the 22K resistor. Ohms law tells us that 212V / 22,000 = 0.0096A or 9.6ma.
dave
Follow Ups:
Dave, My mistake. I did not put the multimeter test lead into the AMP plug-in instead of the V/Ohm plug-in. My bad. Pat
Hi Pat,
I'm curious whether you are now getting the expected reading?
I strongly suggest you perform the measurement exactly how Dave suggested.
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Dave's method is what I am using going forward. It gives the appropriate current reading.
I think there is something wrong with my multimeter. After reviewing all of the plug-ins on the multimeter, there are actually 2 spots where "current" can be measured. 1) 10A and 2) 200mA. I was using the 200mA plug-in and was getting the bad readings. I think its time to get a fluke.
Pat
Just when you say "appropriate current reading", do you 1) the current expected form the circuit (per Dave's post) or 2) the very high mA you were initially reading? I assumed the former, but some might be assuming the latter...
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
By "appropriate", I am expecting around 9 mA just like dave and others have stated which is supported by the math.
At 100ma,that would mean one triode section dissipates 10 watts and we know it can't do that. If you have any stability issues,I would can the LEDs and go to a high quality cathode resistor.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I would test the meter with an external 9V battery and a 1K resistor to confirm its function.
dave
I must have something amiss with my meter or measurement hookup process. Regarding my process, I disconnect the 22k resistor from the tube pin. Then, I clip one lead of my multimeter to the tube pin and the other lead to the bottom of the 22k resistor. Turn on the power and measure mA. I think this is correct, but let me know otherwise. I still get a very high 100+ mA reading.
Pat, that is not how I would do it. I would perform the measurement precisely as Dave suggested.
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: