RF bipolars RIP

Why is NXP killing off their RF parts? Why not just bump the price 5x or so?

Or rhinestone lettering :-)

Aren't those with the tantalum issues? I don't mind an ugly unit that works for decades. Also, my 7704A ain't that bad-looking. Now the power supply goes zzzt at times but it's around 30 years old.

Probably related to the Nexperia spinoff. I guess neither the Chinese nor NXP wanted their RF jellybeans.

NXP started killing off the BFG series parts some years ago--I used to really like the BFG25A, which was a BFT25A but twice as fast. I did order a reel of BFG403W (the 17 GHz version), but I expect its Early voltage is fairly putrid by comparison. Still, they were on sale for 9 cents, so it was worth a roll of the dice since there won't be another chance.

Next reel will be BFT92s.

Cheers

Phil Hobbs

The SPICE model in the BFG403W datasheet has VAF=36V, vs. 50V for the BFT25A. So not as putrid as all that.

Cheers

Phil Hobbs

What was so special about the actual trannie you were speaking about? I mean your emphasis on it being a 600mW device? Why is that such a big deal? There are plenty of RF trannies that can dissipate that sort of power.

It's a SOT89 5 GHz PNP. Output capacitance is 2 pF. I work wideband, time domain, so I can't tune out capacitance.

Thing is, I can't find an equivalent anywhere. There is some 600 MHz Ft stuff, but that's too slow. The SOT23 types would fry at 600 mW.

I wonder how much power a SOT23 or SC70 transistor could dissipate with radical top-and-bottom heat sinking. Gotta try that.

Some day, I'm going to try to build a proton triode. Just to see how truly awful its performance is.

Should be, if one can arrange a comparable density of space charge, at low energy, into the space of what's otherwise a normal e.g. 12AX7 cathode, it'll be a paltry ~1umho transconductance.

Would be fun to see the transit time on a nearly human scale (well, us instead of ns), though.

Tim

Tsk...

Truly, the art of the peaking coil has been long lost...

(Not that you necessarily want to do it in a production setting, but hey, you're the one conflating "can't" with "won't". ;-) )

Tim

Peaking coils only get you a factor of 1.4 (series peaking) to 2.8 (constant resistance T-coil). Not chopped liver, but not a factor of 8 either.

Cheers

Phil Hobbs

I am so glad I gave up discrete design for asic design over 20 years ago...

-- Kevin Aylward

What is nowadays considered full-blown voodoo is when you break off a piece of ferrite, dip into into a drop of liquid nails construction glue because that's what they had around, stick it next to a trace and suddenly everything miraculously quiets down.

"What's that pill you glued in there?" ... "Oh, that? Soylent Green".

Re-designs triggered by component obsolescence are part of the revenue stream for circuit design engineers. As long as it was not the caused by them or at least it's been a few decades.

You could add a grid to an alpha or beta battery. It would need a lot of grid control voltage.

Oh, I'm doing that already. 2 pF is a heap of capacitance, and every picosecond counts.

I enjoy discrete design. I can hack a breadboard myself in an afternoon, or get a board in a week. And an iteration doesn't cost megabucks.

The thing that I'm designing could maybe be done in an IC, but nobody does. Well, I think ADI does but it's not public.

I soldered a flap of copper tape across the top of a power opamp with a heat pad.. soic-8, it helped some.

George H.

Where you getting the protons? Hydrogen plasma? (I'd love to find a cheap way to make protons... Diode laser-Lamb shift- somewhere near 650 nm.

I've always wanted to make an ionic resistor (in water) and measure the Johnson noise...

About equally useful.

George h.

Oh sorry, I thought I was responding to Phil H. Do you know what the Lamb shift is?

George H.

All resistors of a given value must have the same Johnson noise. Unless there's something electro-chemical or photoelectric or something extra going on.

They don't all have to have the same shot noise.

Or bubble noise.

I wonder if the mass of ions changes the frequency response.