Unstable RF amp.

Ft is a function of collector current; nominally incerases linearly with collector current. When internal resistances become dominate due to "high" current (Rbb', Re' mainly) then that breaks down. At a given current, measure the gain at a given frequency F and the gain at 2*F and extrapolate; verify that the gain is one near that extrapolated frequency.

Try building a ring oscillator with two or four of them, with low-value collector resistors and small RF chokes.

Or just look them up in an old GE handbook? Quite often available on eBay for cheap.

But they could often be pushed much higer, IIRC the 2N169A was rated only to 7MHz, but it was possible to build regenerative receivers up to

Or tell me the part numbers, I have several old GE handbooks.

Why not give the garbage man his due. I can probably guarantee that a

Tam

Ge=Germanium not GE

That's an NPN isn't it? - might not work too well in a 60's/70's radio, and I'd have to recalculate the bias resistors for a Si transistor!

In particular the Ft is known for the AF11x family of RF transistors, as I have these listed in a Mullard data book. A curious point is both the AF116 & AF117 have Ft listed as 75MHz yet the 116 was sold for use in 10.7MHz FM/IF strips and the 117 is only deemed suitable for AM L/O & 455kHz IF strips - almost all the specifications are identical so what makes the 116 &

There are also non Pro-electron numbered Ge transistors in the bits box with no easy way of distinguishing between RF & AF types especially Newmarket "NKT" types It would be handy to be able to classify these.

One contributor to this thread suggested a ring oscillator, at first glance this didn't look very helpful since I suspect that the oscillator might be limited by the slowest transistor in the ring. On the other hand, if there is no problem mixing Si & Ge transistors in the same ring, I'm sure I can find a few PNP RF Si transistors that far outperform the Ft of the Ge ones I want to test. Hopefully then the Ge transistor in the ring would be the slowest - and limit the maximum frequency the ring can oscillate at. Am I anywhere near on this?

TIA.

In message , dated Sat, 19 Aug 2006, ian field writes

Something not given on the data sheet. It probably has only nominal values for Ccb, for example, but the AF116s are selected for lower values.

Unusually that spec is given and its a short form data book not a proper data sheet! IIRC the values are identical for both devices - but measured at the respective frequencies.