"klem kedidelhopper" wrote in message
...
On Jun 4, 5:59 am, "Michael A. Terrell"
wrote:
isw wrote:
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.
There is a 100% chance that you're wrong:
http://www.nteinc.com/specs/100to199/pdf/nte160.pdf
This link was also posted in the original thread: AM/FM radio
troubleshooting
--
It's easy to think outside the box, when you have a cutting torch.
Yes I am aware of the reversal of emitter and base leads between the
two types. I was very careful with that. I triple checked the
connections each time I removed the 160 and then re installed it. The
radio does in fact work intermittently as it did before each time the
old transistor is installed back in the radio so at this point I can
still get back to square one, thankfully, (as long as the foil doesn't
start lifting from the phenolic board). The ohmmeter confirms the
original as well as the 160 as being a PNP Ge transistor too.There is
somewhat of a difference in reverse ohmmeter readings between the 160
and the AF126 but I would have suspected that from germaniums,
especially one old one and one new one anyway. Although it really
shouldn't be necessary I did a search for an AF126 but the only thing
that came up were some old spec sheets. I think that this one sadly is
long gone. I did initially try the 160 in the circuit with the metal
can lead disconnected. I didn't think that this would make any
difference because when troubleshooting the chassis originally I was
looking for "whiskers" as suggested to me before as possibly being the
case. So I had lifted all the can shields from all the transistors
and that didn't make any difference. The radio still worked
intermittently. So I did finally solder the can lead on the 160 on but
it still did not work, I don't want to touch the alignment because I'm
just not convinced that this is where the problem is. I know that
NTE's don't always work in the particular application but I wonder if
perhaps this is whats going on here. I just can't help wondering if
I'm missing something else though. If anyone has any further thoughts
on this I would be most sincerely grateful. Lenny
OK. Let's apply a little genuine fault-finding here. When the radio goes
off, does it stay off, or does it come back on as soon as you bring any test
gear near it ? If it stays off, then you need to split the circuit down at
the mixer. When it's working, use a 'scope to check the level of the local
oscillator. Look at its frequency, and watch it move as you tune from the
top to the bottom of the band. When it goes off, recheck. If the LO signal
is still there, and of the same amplitude and frequency as it was before,
then the problem is south of that point in the IF or detector stages. If
anything has changed with the LO signal, then the problem is north of there.
The LO / mixer might well be all the same stage. It was very common to use
self oscillating mixers back in the days of Ge transistors. It was also
common to use a winding on the ferrite rod as part of the L for the
oscillator. Been a long time now, but I seem to recall them being called
Reinartz (sp?) oscillators ?? As a slight aside, when a radio 'dies' like
this, the AM IF stages can often be checked as being basically functional,
with a screwdriver and a finger. Touching the base legs of the IF
transistors will often result in some local AM station being picked up
'thinly'. Again, it's been a long time, but I seem to recall that
intermittent faults like this often came down to those polyester silver foil
and clear plastic cylindrical caps (they used to be made by a company called
Suflex) and intermittent high value resistors. If the radio uses any of that
type of cap in the LO / mixer/ RF stages, then when it goes off, just give
each one that you can get at, a gentle squeeze with a pair of long-nosed
pliers.
Arfa