"Michael A. Terrell" wrote in message
m...

Arfa Daily wrote:

"klem kedidelhopper" wrote in message
...
On Jun 8, 10:51 am, spamtrap1888 wrote:
On Jun 7, 4:40 pm, Archon wrote:



On 6/7/2011 5:47 PM, klem kedidelhopper wrote:

On Jun 6, 9:37 pm, wrote:
If the radio is intermitent it does not mean that necessarily the
transistor, i think of one probable cause is the variable
capacitor
besides if the transistor you mentioned is part of the if
section
then you may check with another radio tuning a frequency so
produces
an harmonics in the good radio so you know the mixer stage is
working
then you can inyect a signal with your finger in the base of the
first
if transistor and a radio station should be heard. Have you tried
to
resolder all points and verify all paths are in god condition.
Hope
it
can help.
rgds

On Jun 4, 2:39 am, klem

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?
Thanks,
Lenny

Hi...
I can send You a AF126. You pay the postage, the transistor You
can
have for free.

Bo-Lennart Karlsson
Falun, SWEDEN

Hi, What do you think the postage to the US will be? Thanks,
Lenny-
Hide quoted text -

- Show quoted text -

Well the odd thing is that the radio always starts out working
perfectly. It will run consistently for anywhere from ten minutes
to
sometimes two hours. It seemed that at first operating it at low
volume settings may have precipitated the problem but now I'm not
so
sure about that. However once the intermittent condition begins it
continues until the unit is shut off for a period of time. After
that
the period of time it takes for the intermittent condition to
start
again after a subsequent power on is directly proportional to the
time
the radio has been off. I managed to measure all transistor
voltages
during an "OK" period. I then took similar voltage readings during
failure. As expected all voltages on all transistors were
affected,
however the voltages measured at the terminals of this particular
transistor in question are all the same, (about 3.0volts) when the
failure condition occurs. It was for this reason i suspected this
transistor, (as improbable as this may seem), of developing what
looks
like a "dynamic" b e c short. Lenny

Cracked volume control pot

In that case he could temporarily replace the pot with two resistors,
right? And see if the circuit goes intermittent.

Because it always starts out working, and this is definitely
consistent. I really feel that this is an active component problem.
Lenny

If you have the schematics for the radio, then it should be no problem
figuring out what is going wrong. There really can't be very much that
could
cause all three terminals of the transistor to assume the same voltage.
Something amiss with the emitter return maybe ? If the base is biased
with
respect to ground, and the emitter is returned to ground, then you must
measure a difference between the base and emitter, equivalent to a
germanium
P-N junction drop. If the emitter return goes open, then you might well
read
(almost) the same voltage at the emitter and base, and possibly the
collector too.


It's a PNP transistor. The emitter has the highest voltage, so it is
something opening in the collector path to ground. When it opens, the
base voltage rises because the transistor is no longer biased properly.


I haven't got a copy of the circuit to hand, but I'm not sure that I
understand what you're saying. A PNP circuit is just the same as an NPN
circuit, but with the battery upside down. Ground is ground and bias is
bias, applied between the base and emitter. Doesn't matter whether it's a
PNP or an NPN transistor, the ground reference is just the opposite pole of
the battery. The emitter having the "highest voltage" is basically an
arbitrary term as that voltage could be 'higher' in a positive or negative
direction, depending on where you are taking to be your measurement
reference. Things get a little more complicated to get your head around,
where the circuit is powered the 'conventional' way up, but the transistors
are in upside down. Maybe that's what you're saying here ?

Arfa