Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
A noninvasive SR-series Direct Reading Plate Current Meter
¿ªÔÆÌåÓýSorry in advance if this has already been done.? I know people will often connect up a VOM to measure the voltage drop across the 10 ohm resistor in the PS-120 or PS-500 power supplies to monitor the Plate idle current.? As most know 0.7V for an equivalent 70mA current.I was contemplating a noninvasive method to provide a better ¡®almost¡¯ direct plate current measurement.? By noninvasive, I mean using the same 10 ohm resistor in the power supplies via their Tip Jack connections.?? Then it dawned on me, I have a decent assortment of meters, so why not use a 0-500uA meter and simply divert 1/1000th of the current going through that 10 ohm resistor.? Robbing 1/1000th your plate current will go without notice under normal operation.? For 200mA of plate current I¡¯d be diverting 0.2mA of current, barely noticeable. Found a nice vintage Triplett 500uA FS DC meter in my junk box.? It was actually NIB!??? The schematic couldn¡¯t be simpler.? I have essentially around 10K of adjustable resistance in series with the meter and it gets connected to the same power supply TIP jacks that everyone uses to monitor the idle & plate current (via voltage).? Even though the schematic shows a 5K fixed resistor and a 5K pot, I naturally used a 4.7K resistor and a 10K series connected (recommended) pot.? Ain't much current going through these components so high wattage is not of concern. Calibration is supper easy.? Either using a DC power supply or even a low voltage, one to three volt, battery connect the meter circuits leads to the DC source.? Then adjust the pot to correspond to which you measure with either your VOM or better yet with a decently accurate DMM.?? So for a battery that measures 1.5VDC you would set the meter to read 150.?? Once adjusted it will never need adjustment again! I installed the meter in a case, I also had lying around, and painted it in a similar two tone Hallicrafters gray, or the best I could get using off-the-shelf spray paint.? Notice, I just added a decal to the front of the meter face that indicates the reading is X1000.? So 70 on the meter is 70mA, 200 is 200mA, etc. No more old VOM¡¯s needed and I have a continuous noninvasive method for monitoring the plate current on my personal SR-150 transceiver. 73 Don N9OO |
to navigate to use esc to dismiss