Roberts R300 transistor replacement

[Krolroger]

Hello all,

This is a most useful site. My main area of interest has been B&O up to about 1978, but I am currently trying to sort out a Roberts R300 with the usual AF117 problems.

I replaced the first AF117 at the front end with an AF127 but was rewarded with silence. I tried another one with the same result.

So I am wondering if I got the pin out correct. I presume the data sheet is read as if looking at it from underneath.

I normally use a Peak DCA55 tester to determine pinout, but in this case it just identified the AF127 as a "3 terminal bi-coloured LED" which also is how it identified the intermittently faulty AF117. I would expect it to identify a germanium pnp transistor.

I'm just wondering whether the both of the replacement AF127 are faulty.

Anyway, I put back in the AF117 and left the shield leg disconnected, and the set works at least for now.

Any thoughts about pinouts, Peak testers on germanium semiconductors etc will be gratefully received.

Regards,

[Station X]

Hello and welcome to the forums.

I just tested an AF127 using a DCA55. It was correctly identified as a PNP germanium transistor with an hFE of 50.

That is so long as you connect the DCA55 to the C, B and E. Make a connection to the screen and it tests as LED or doide junction(s).

I've also have known the DCA55 to identify faulty transistors and other three legged devices as "3 terminal bi-coloured LED".

[paulsherwin]

It's easy to miswire the AF12x series.

[Herald1360]

Pinouts for AF12x and Russian GT322B devices referenced here:

https://www.vintage-radio.net/forum/...5&postcount=36

HTH

[Krolroger]

Hi, thanks for your replies.

I suspect faulty replacements, as I made connections to BCE. Annoying, as they're not cheap.

I should have trusted the Peak before I got soldering.

I think I will try the zapping trick.

Regards,

[Station X]

Where did you get your AF127's from?

[Steve_P]

Do you get the hiss or not?

If no go for the IF transistors. If yes check the voltages and also the coils.

Cheers,

Steve P,

[Krolroger]

Hi, thanks for all your replies.

I guess if the Peak identified all three new AF127's as "3 terminal bi-coloured led", and the faulty, though semi-functional AF117 likewise, the probability is that they are duff. Connections were made to BCE, not screen.

Annoying as they weren't cheap.

Hmm, might try the zap method.

Regards,

[Krolroger]

SWLE2000 on ebay. Speedy service.

[mhennessy]

Originally Posted by Station X

I've also have known the DCA55 to identify faulty transistors and other three legged devices as "3 terminal bi-coloured LED".

I've also experienced this one many times... Had one earlier today. Out of interest I put it on a breadboard with a simple LED+resistor in the collector circuit, and the leakage was so bad that the LED lit up (about 3mA). But connecting the base to emitter caused the LED to go out. Connecting the base to -6V via a 100k resistor caused the LED to get slightly brighter.

The transistor works perfectly now that it's back in the circuit.

Peak Atlas themselves explain how even the best transistors can get caught out by leaky germanium transistors.

[Krolroger]

Just to clarify, does that mean that the "3 terminal bi-coloured led" message on the Peak is always indicative of a faulty transistor?

Reagrds,

[ronbryan]

I have just bought some AF127 transistors from a UK vendor on Ebay for a Roberts R200. Although marked as AF127, I found that the base and emitter connections were reversed. The only other markings are PH above the part number and m0532 below the part number.

I cannot tell who manufactured them, but they are distinctive, as although the TO-72 case is the normal size, they have a slightly domed top rather than flat as I would have expected from previous experience of many of this type. Another difference is that the part number is printed on the top of the transistor in very small characters, rather than in larger characters around the side of the case as is normal for AF127 in my experience.

Ron

[Station X]

Originally Posted by Krolroger

Just to clarify, does that mean that the "3 terminal bi-coloured led" message on the Peak is always indicative of a faulty transistor?

Reagrds,

I can only relate my own experiences. An AF127 purchased from RS Components tested good on a DCA55. I didn't bother identifying specific leads, as the DCA55 does that for me.

On another occasion a faulty transistor (not working in a circuit) was identified as a "3 terminal bi-coloured led" as related in post #22 in this thread:-

http://www.vintage-radio.net/forum/s...d.php?t=136568

[mhennessy]

Originally Posted by Krolroger

Just to clarify, does that mean that the "3 terminal bi-coloured led" message on the Peak is always indicative of a faulty transistor?

Reagrds,

No. Not at all. Please see post #10.

With a typical germanium transistor - which is rather less "ideal" than a silicon transistor - there are all sorts of ways for a tester to get confused. It can only test so much, after all. The acid test is how the transistor behaves in a real circuit.

As there seems to be some doubt about identifying the lead-out of your samples, and given that a tester isn't able to reliably do this for us, I'd get a bread-board and test the transistor in a simple circuit (just a couple of resistors would do).

[Krolroger]

These slightly dome-top TO-72 are the same as mine, then.

I will swap base and emitter connections and see where I get.

Thanks for all your help.

[ronbryan]

Of the six AF127 transistors that I recently bought from the UK vendor that Krolroger detailed in post #9, five had base and emitter reversed (as I said in post #13), but the last one was base-emitter open circuit and consequently useless. I used an Avo 8 on the ohms x1 range for junction testing.

Ron

['LIVEWIRE?']

For at least a couple of years now I've replaced AF11x transistors with Russian GT322 devices. The long (about 25mm) leads on these make them easier to fit than the AF12x transistors, besides which they are, or were the last time I checked, about £1 each in quantitties of 10 or more, much cheaper than the AF12x types.

[paulsherwin]

Originally Posted by Krolroger

These slightly dome-top TO-72 are the same as mine, then.

I will swap base and emitter connections and see where I get.

Thanks for all your help.

There are indeed different leadouts around, and beginners often get caught out. You can usually determine the correct leadout using the hfe test function found on most cheap DMMs - just swap them around until you get a plausible reading.

[Station X]

Some posts moved to a new thread here:-

http://www.vintage-radio.net/forum/s...d.php?t=141122

[Herald1360]

E B reversed on AF12x corresponds to the Russian device pinout. Enterprising labelling to command higher price, perhaps?