EMRFD Message Archive 7550

Message Date From Subject
7550 2012-06-24 10:32:29 ka3j12 BD139-6 versus BD139-16
Which version is best for use as an HF xmtr power amplifier? The -16 version has higher HFE but that's a DC figure and there's no specs directly related to HF use since this is really a switching transistor. Anyone have actual experience or can take a good guess? Thanks!

Ron (KA3J)
7551 2012-06-24 11:53:47 Ashhar Farhan Re: BD139-6 versus BD139-16
use what you have.
- farhan

7552 2012-06-26 16:25:39 RW Mail List A YouTube video using voltage drops to show how a Op-Amp circuit wor
Hi all,

I’ve made a small YouTube video that uses voltage drops to show the gain and how a Op-Amp circuit works.


Using voltage drops to understand how operational amplifiers (op-amp) work. That is to use the voltage drops across Rin and Rf (R feedback) to see the gain of the amplifier. If the current through two series connected resistors are the same, then the voltage drop across the 6k ohm resistor will be twice the voltage drop across the 3k ohm resistor. Note: the (-) and (+) inputs will be at the same voltage if the amplifier is working ok. That is, virtual ground for the inverting op-amp circuit, and the input voltage for the non-inverting op-amp circuit.


Roderick Wall, vk3yc.

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