Old radio, old transistors, old me...

[elmontador]

Hello, i have a old car radio (Blaupunkt FTZ-NR. U 108) AM FM mono, that uses 2 transistors (AD156 pnp, AD157 npn), i need to replace the transistors but its been  a headache try to find a replacement.
I found the following info online

Type Designator: AD157
Material of Transistor: Ge
Polarity: NPN
Maximum Collector Power Dissipation (Pc): 8 W
Maximum Collector-Base Voltage    |Vcb|: 32 V
Maximum Collector-Emitter Voltage |Vce|: 16 V
Maximum Emitter-Base Voltage  |     Veb|: 10 V
Maximum Collector Current         |Ic max|: 2 A

Max. Operating Junction Temperature (Tj): 85 °C
Transition Frequency (ft): 1 MHz
Forward Current Transfer Ratio (hFE), MIN: 50
Package: TO8

the only equivalent (allegedly) i found searching the internet is NTE131 NTE135 that are also obsolete
i know that i can by on eBay old parts, but i don't want to wait a month just to find out that the transistor is a fake or does not work.
I would appreciate some advice from you guys. THANKs

[Cyberdragon]

NTE155:

http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=AD157

AD157:

https://www.donberg.ie/catalogue/semiconductors/semiconductors_a-ay/ad_157.html

(note: min. order 20EUR)

AD157:

https://radio-antigua.com/ad157transistornosnewoldstock1pcc339u24f230514-p-603919.html?language=en

(more expensive)

[elmontador]

Thanks for the info, i wanted a modern replacement (i don't care about the transistor package) so i can buy it locally, if i don't find it i think i will stick with your second link cause i am in Europe.
THANKs.

[oldway]

You could replace them by AD161 and AD162, easier to find than AD156 and AD157.

[exe]

Why not use digikey ([1]) filter to find what parts would a good replacement? Then just look what is available on the local market (or order from digikey, they deliver to EU too, although I never tries this by myself). Or you can buy something from tme.eu, they are in Polland and offer EU delivery. Or any other available distributor like rs-online, farnell or something. Most of them have parametric search (but not many transistors in metal can enclosure, unfortunately). Although, I can't really guarantee that replacement will work the same way as AD156. But I'd try to find parts similar in collector current, power dissipation, Hfe (if possible), and maximum frequency.

[1] https://www.digikey.com/products/en/discrete-semiconductor-products/transistors-bipolar-bjt-single/276?FV=df00070%2Cdf0000d%2Cdf00011%2Cdf000d2%2Cdf00023%2Cdf00031%2Cmu2.2A%7C2101%2Cmu2.4A%7C2101%2Cmu2.5A%7C2101%2Cmu2.6A%7C2101%2Cmu2.7A%7C2101%2Cmu2A%7C2101%2Cmu3A%7C2101%2Cmu10W%7C2109%2Cmu12.5W%7C2109%2Cmu14W%7C2109%2Cmu15W%7C2109%2Cmu20.8W%7C2109%2Cmu20W%7C2109%2Cmu23W%7C2109%2Cmu24W%7C2109%2Cmu25W%7C2109%2Cmu26W%7C2109%2Cmu28W%7C2109%2Cmu29W%7C2109%2Cmu30W%7C2109%2Cmu7W%7C2109%2Cffe00114&quantity=&ColumnSort=0&page=1&pageSize=25

[oldway]

AD161 and AD162 are germanium transistors, not silicium....A germanium transistor can't be replaced by a silicium transistor without modifications of the circuit.

A as first letter means "germanium" and B as first letter means "silicium".

[bd139]

I used to bung Si transistors in Ge circuits when I was a kid and they mostly worked. Worth a try. BC179 was the magic bugger that worked mostly.

Edit: those look like PA transistors. Risky business.

[oldway]

These AD's are germanium power transistors in TO66 case.

1) I doubt a lot that you could replace germanium power transistor by silicon in a classe B audio output stage : You will have serious problems of idle current with high THD because Vbe of a germanium transistor is 0.3V and that of a silicon is 0.6V

2) Even silicon power transistors in TO66 case are not that easy to find.
You find such transistors in Marantz 4240 and in Luxman SQ700X (2SD155 and 2SA616)

[exe]

Right, I completely missed these are germanium.

If you have schematics we could try to modify it to fit modern transistors. Although, it would be interesting how it would work with silicon transistors. I'd say there should be a lot of distortion for low amplitude signal, but I have no experience with amplifiers.

[IanMacdonald]

You could probably use TIP41/42 silicon TO220 replacements so long as you increased the interbase bias voltage to just below where they start to conduct. Generally the best way to do this is to use a 'Vbe multiplier' arrangement.

It will probably work without modification but will have high crossover distortion.

[oldway]

You could probably use TIP41/42 silicon TO220 replacements so long as you increased the interbase bias voltage to just below where they start to conduct. Generally the best way to do this is to use a 'Vbe multiplier' arrangement.

It will probably work without modification but will have high crossover distortion.

Non sense, you find AD161 / AD162 cheap and easy !!!
https://www.ebay.de/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR0.TRC0.H0.Xad161.TRS0&_nkw=ad161&_sacat=0

I don't know if the url will work, if not, look for AD161 on ebay.de (Germany)

[bob225]

you can use silicon but you will need to adjust resistor values to suit you can get away with near spec transistors

You may want to read this page I come across on the search for AD and AF transistors info

https://www.markhennessy.co.uk/articles/vintage_transistors.htm

I have just started working on some Roberts radios my self, its a bit of a learning curve

[oldway]

In repair, we try to simplify life, not to complicate it with doubtful modifications of circuits.
Otherwise, we do not repair anything, we waste time.
The only frequent and justified modifications are to replace some lamps hard to find or expensive by LEDs.

Here there is no reason to change anything.

AD161 and AD162 can be used.

Besides the drivers transistors are probably also to replace .... AC127 / AC128 probably.

Remember that we must take precautions to solder germanium transistors....