Re: 577 AC collector supply not reading zero on display

 

Hi DW,
If the 577 is showing 2 horizontal divisions at 50mV/Div that implies there should be 100mV p-p between emitter and collector banana jacks. If that voltage is a really there then we can measure a current using a 100 ohm resistor.

Put the resistor between the emitter and collector in the left set of banana jacks and flip the left / right switch to the left. Set the series resistor to its smallest value of 0.12 ohms. You should get 1ma of current from 100mV through a 100 ohm resistor. If you set the vertical knob to 0.2ma/ Div you should get a DIAGONAL LINE that goes from 0V and 0ma (the lower left corner) to 2 divisions (100mV) horizontal and 5 divisions (1mA) vertical. If you switch the collector supply from NPN to PNP the diagonal line will move to the upper right corner.

Dennis Tillman W7PF

-----Original Message-----
From: DW
Sent: Sunday, December 01, 2019 6:17 PM
Subject: Re: [TekScopes] 577 AC collector supply not reading zero on display

<SNIP>
With the collector in AC on 6.5V with 2k series resistor, horizontal devision set to 50mV...
A flickering line appears 2 divisions in length I find if I increase the D1 brightness (Turn the D1 brightness fully clockwise) the flickering pattern goes away into a solid green light which is interesting to note I plugged a voltmeter into the Emitter and collector terminals and observe 38mV of AC voltage I short the emitter and collector terminals and find the 2 division line shrinks to a dot and the voltmeter reads about 0mV AC Obviously some small amount of AC power is getting through and measured on the display and voltmeter




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Dennis Tillman W7PF
TekScopes Moderator

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