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. http://www.youtube.com/watch?v=YdgeMNTA-7Y 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. Regards, Roderick Wall, vk3yc. ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.1913 / Virus Database: 2437/5095 - Release Date: 06/26/12 [Non-text portions of this message have been removed]

Hi all,

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

http://www.youtube.com/watch?v=YdgeMNTA-7Y

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.

Regards,

Roderick Wall, vk3yc.

-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.1913 / Virus Database: 2437/5095 - Release Date: 06/26/12

[Non-text portions of this message have been removed]