Germanium transistor sub

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

Reply to
klem kedidelhopper
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AF126 and NTE160, appear to have different pinouts ?

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Arfa

Reply to
Arfa Daily

Even if the transistor's output capacitance was far-enough "off" to significantly detune the IF, you'd still get something. *

Are you certain you installed the NTE 160 with the leads in the right positions?

What happens when you put the old transistor back?

You should also check the transistor with a diode-safe ohmeter.

  • I assume the designer would take the base-collector capacitance into account when designing the IF transformers. You'd want the latter to have significantly higher capacitance so that swapping transistors wouldn't cause a big shift in tuning.
Reply to
William Sommerwerck

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.

Isaac

Reply to
isw

There is a 100% chance that you're wrong:

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This link was also posted in the original thread: AM/FM radio troubleshooting

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It's easy to think outside the box, when you have a cutting torch.
Reply to
Michael A. Terrell

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

Reply to
klem kedidelhopper

Inasmuch as the NTE device is spec'd for this sort of application, it seems very strange you don't get something out of it.

It IS possible you have the leads reversed. I'm sure anyone in this group will confirm that one can make the same mistake over and over and over and not catch it. Make sure the E and B leads aren't touching.

The next step is to confirm that the replacement transistor is actually good, regardless of the ohmeter readings. Check the bias. Are the voltages correct? Or is the transistor saturated or cut off?

If the bias is correct, put a 'scope and input and output, and see what's there.

You might also build a simple amplifier using a GE Transistor Handbook circuit, and see whether or not it works.

Barring some weird mistake on your part, I'm going to go with Sherlock and state that, as we've eliminated all the impossible stuff, the only thing logically remaining is that you have a bad transistor.

Reply to
William Sommerwerck

Or the obvious, the transistor wasn't at fault to begin with.

Jeff

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"Everything from Crackers to Coffins"
Reply to
Jeffrey Angus

Which is where I would start :)

Jamie

Reply to
Jamie

e.

I'm having a hard time picturing how one would swap B and C. Is the substitute mounted high above the board?

To see if the AF160 is good or not, and to make sure the NTE is a match: could you call a community college or tech hs to see if they had a curve tracer you could use? Then you could compare to those spec sheets you downloaded.

Reply to
spamtrap1888

Ummm... could you take a 2nd look at the model number? Grundig makes the YB-305, but that's not germanium.

Grundig also makes a 3059, but that's tubes:

Perhaps if you disclosed the correct model number, and possibly which xsistor you're replacing, we can find a schematic, and determine if your NTE substitute is appropriate?

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Reply to
Jeff Liebermann

Once again: Check the Collector voltage. That will show if the transistor is properly biased, and if it is a good transistor. If it isn't in the ballpark of a similar radio, look for the cause. Shorted capacitors in IF cans was a common failure, but well below bad & intermittent transistors.

I serviced hundreds, if not over a thousand transistor radios in the '60s & early '70s. I never saw a radio that needed alignment after replacing a transistor, unless someone had played with it. Some were poorly aligned from the factory, but those were generally the ones that sold for less than $20 new.

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It's easy to think outside the box, when you have a cutting torch.
Reply to
Michael A. Terrell

"klem kedidelhopper" wrote in message news: snipped-for-privacy@j28g2000vbp.googlegroups.com...

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

Reply to
Arfa Daily

A lot of Grundig radios are almost impossible to locate schematics for. One radio with his (Transistor) TR-305 model number was for sale recently on Ebay.

The newest 'TR' series listed in Sams is the TR-17, and date 1965. There are no YB models listed in Sams, BTW.

It uses four AF126 transistors in the AM/FM IF Amplifier stages. Sams shows the collector voltages at 0, because each collector goes to ground through the primary of each pair of IF transformers. A modern meter will still show some voltage at the collector, but a VTVM used by Sams would barely make the needle move. The schematic shows between 4 - 6 ohms to ground from each collector.

He said it was AF126, which does cross to ECG/NTE 160.

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It's easy to think outside the box, when you have a cutting torch.
Reply to
Michael A. Terrell

ams

A lot of good information guys. I'm sorry I didn't include it in this new post but the radio model is "Transistor 305".It was given to me around 1970 and it wasn't new then so I'm guessing a bit here. It is late 60's vintage I think. And I do have a schematic and foil side board layout too.I did buy two of these 160's. (I wasn't going to open the second if I didn't have to as they were 5.50 apiece) but maybe this one is bad. I didn't think I'd have to touch the alignment either Michael. Just figured that it would work even somewhat.Lenny.

Reply to
klem kedidelhopper

When it isn't working, check the signal at the collector of each IF amp with your scope. Any shop scope will display an AM IF. If it disappears at some stage, find out why. If it is missing at the mixer output, check continuity on the first IF transformer.

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It's easy to think outside the box, when you have a cutting torch.
Reply to
Michael A. Terrell

As I said, you should have been getting something, even if the IF alignment wasn't spot-on.

$5.50? Ouch!

Be careful handling the device. Transistors can be damaged by static electricity. When opening the box, after -- uh -- discharging myself, I'd dump the transistor onto a piece of aluminum foil, then roll up the transistor in the foil until I was ready to insert it.

Reply to
William Sommerwerck

I've even got away with replacing transistors in UHF tuners most times I attempted it.

Reply to
Ian Field

In contrast, most of their TVs had a service sheet stowed in a slot inside the cabinet.

Reply to
Ian Field

I did it all the time in CATV converters where the L.O. was at 1.1 GHz. You had to bend the leads exactly like the original.

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It's easy to think outside the box, when you have a cutting torch.
Reply to
Michael A. Terrell

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