EMRFD Message Archive 8132

Message	Date	From	Subject
8132	2013-01-20 08:21:46	Ravi Miranda	BFR91 equivalent
Hello I'm trying to find an equivalent for the BFR91 but since my junkbox is limited can I use PN2222A or 2N3904 if I don't exceed the fT? Say I limit the Frequency to 50Mhz or so? Just want to build a buffer between stages, over the weekend :-) Thanks in advance. 73 Ravi -- I'm here to add more value to the world than I'm using up. [Non-text portions of this message have been removed]
8138	2013-01-20 11:13:25	Ashhar Farhan	Re: BFR91 equivalent
ravi, BFR91 may be even contraindicated if you are using the transistor below 50 MHz. Given the high beta, it can break-out into oscillations unless you bypass it well at microwave frequencies as well! It is better to stick to 2N3904/2N2222 etc for HF to lower VHF work. - farhan
8140	2013-01-20 12:56:58	Ravi Miranda	Re: BFR91 equivalent
Farhan Thanks for the tip. The original circuit was meant for VHF work hence the BFR91, but I am trying to experiment with what I have currently lying around, and that was the 2N3904 and 2N2222A. I will use a lower frequency VCO and the MC145190 controlled by the AMICUS to learn how to use the SPI bus. Thanks for the support. Will give them a try. 73 Ravi On 20 January 2013 19:13, Ashhar Farhan <farhanbox@gmail.com> wrote: > ravi, > BFR91 may be even contraindicated if you are using the transistor below 50 > MHz. Given the high beta, it can break-out into oscillations unless you > bypass it well at microwave frequencies as well! > It is better to stick to 2N3904/2N2222 etc for HF to lower VHF work. > - farhan > >
8141	2013-01-20 12:57:13	Jim	Re: BFR91 equivalent
fT = the frequency at which gain =  unity. So ... you'd not want to use a transistor with unity gain as a buffer, since the normal circuit losses would make it an attenuator when everything was said and done. If you have genuine 2222s or 3904s they should work fine. If they are Chinese, Malaysian, or Indian counterfeits?  Maybe not so much. Conveniently, pulls from 30-year-old junk are almost always premium parts.  So sometimes it's better if some of your junkbox actually came from junk. 73 Jim N6OTQ >________________________________ >
8142	2013-01-20 16:26:11	kb1gmx	Re: BFR91 equivalent
8144	2013-01-20 22:00:12	victor	Re: BFR91 equivalent
There are a few transistors with Ft from 600MHz to 1GHz that are better for sub-100MHz circuits: 2N918, MPSH11, 2N5179. Its interesting to find whether there are more types that are easier to buy (ebay?). Victor - 4Z4ME