Maker Pro
Maker Pro

Unstable RF amp.

I

ian field

Jan 1, 1970
0
Is there a quick'n'dirty way to estimate the useful frequency limit of old
Ge RF transistors? - I was thinking of maybe an inherently unstable untuned
RF amp that would tend to oscillate at the highest frequency that the
transistor gave useable gain!
 
R

Robert Baer

Jan 1, 1970
0
ian said:
Is there a quick'n'dirty way to estimate the useful frequency limit of old
Ge RF transistors? - I was thinking of maybe an inherently unstable untuned
RF amp that would tend to oscillate at the highest frequency that the
transistor gave useable gain!
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.
 
A

Ancient_Hacker

Jan 1, 1970
0
ian said:
Is there a quick'n'dirty way to estimate the useful frequency limit of old
Ge RF transistors? - I was thinking of maybe an inherently unstable untuned
RF amp that would tend to oscillate at the highest frequency that the
transistor gave useable gain!

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
21MHz with them.


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

Tam/WB2TT

Jan 1, 1970
0
ian field said:
Is there a quick'n'dirty way to estimate the useful frequency limit of old
Ge RF transistors? - I was thinking of maybe an inherently unstable
untuned RF amp that would tend to oscillate at the highest frequency that
the transistor gave useable gain!
Why not give the garbage man his due. I can probably guarantee that a
2N2369A switching transistor will run circles around the GEs.

Tam
 
I

ian field

Jan 1, 1970
0
Ancient_Hacker said:
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
21MHz with them.


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

Ge=Germanium not GE
 
I

ian field

Jan 1, 1970
0
Tam/WB2TT said:
Why not give the garbage man his due. I can probably guarantee that a
2N2369A switching transistor will run circles around the GEs.

Tam

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!
 
I

ian field

Jan 1, 1970
0
Robert Baer said:
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.

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 &
117 different?!

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.
 
J

John Woodgate

Jan 1, 1970
0
dated Sat said:
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 & 117 different?!

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.
 
I

ian field

Jan 1, 1970
0
John Woodgate said:
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.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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.
 
Top