"isw" wrote in message
]...
In article
,
klem kedidelhopper wrote:

I think I've found the transistor that is intermittently failing in my
Grundig 305 transistor radio.It is an AF126. I obtained an NTE 160
which is supposed to replace the AF126. however I installed it and the
radio does not work at all. I wouldn't think that I would have to do
a complete IF alignment after simply replacing a transistor, that is I
would think that even if the new part detuned the circuit slightly, I
would expect to get something through. Any opinions on this?

From the subject, you say the original transistor is a Ge device.

There's a very good chance that the "replacement" is actually a Si one.
You can check this by measuring the forward conduction drop of the B-E
junction -- a Ge one will be about half that of Si.

If the replacement is, in fact, a Si device, you still might be able to
get good performance from it by adjusting the bias point.


There seems to be a consensus of opinion that the OP has indeed selected a
suitable Ge replacement, however I suspect that even if a Si part had been
fitted the consequenses wouldn't be as serious as it not working at all.

Any sort of decent quality radio would have automatic bias common emitter
stages, the base bias is set by a voltage divider - that and the value of
the emitter resistor determine the collector current.

The self compensating nature of the circuit would tend to ensure a
relatively small reduction in collector current, the main problem I can
think of is that AGC is often fed at the bottom of the base bias divider, so
using a transistor with a higher Vbe may have a similar effect to a large
AGC control voltage - very low gain maybe, but totally inoperative;
doubtful.