Re: Ft overhead: Keep in mind that you need more gain than the
minimum that sustains oscillation in the absence of a load -- you
need enough to support the power delivered to a load. On top of
that, you don't want the frequency of oscillation to be affected too
much by the transistor's own phase shift -- you want the resonator
to control it. All those considerations argue for a healthy ft
margin. I'm sure you could sub a somewhat slower transistor and
still get output, but you will sacrifice some of the famous (and
hard-fought) stability for which the HP8640B is prized.
-- Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 4/13/2022 16:44, Flannel Tuba wrote:
toggle quoted message
Show quoted text
Thank you, Arie for finding a link to the actual scanned?
article! Having the pictures along with he text is quite a nice
addition.
Meanwhile, I have ordered a smattering of VHF and UHF
transistors from Mouser with marginally similar ratings to those
Tom provided. I do wonder about the fT of 5GHz though. The
oscillator's range is from 230-550MHz, so I wonder why the
extreme frequency overhead margin. I went ahead and ordered a
dozen or so potential replacements having at least the Vcbo of
30v, Vceo of 20v, Vebo of 4v and fT of over 600MHz with several
in the 1-5GHz range. A couple are TO92 packages, which I
envision just folding the base lead across the top to make
contact with the grounding hex cap nut/cover, but most are
SOT-23, which I'll have to come up with an adapter of some sort
for. Any ideas on this are more than welcome.?
Well, if I'm lucky I'll have some time in the next few weekends
to experiment with possible replacements for the rare and
venerable HP 5086-7082.
I'll let you know what I find.
-Scott?
