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.
I'm here to add more value to the world than I'm using up.
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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.
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
Thanks for the support. Will give them a try.
On 20 January 2013 19:13, Ashhar Farhan <email@example.com> wrote:
> 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.
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