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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 26th Nov 2023, 7:41 pm   #1
kestrelmusic's Avatar
Join Date: Feb 2008
Location: Wrexham, North Wales, UK.
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Default Roberts R200

This is my first attempt at a transistor set, so please be gentle with me!

Basically, there's nothing from the speaker but slight hiss, presumably from the o/p stage.

The first three transistors are AF117's, and from what I read here and elsewhere they are likely to have failed.

Even if I could find NOS replacements they are pretty likely to be duds by now, from what I hear.

However, there seems to be some consensus that AF12x are good replacements. Does anyone have experience of these? There seem to be quite a few around, but they're not cheap and I want to be sure that they are suitable before buying any!
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Old 26th Nov 2023, 8:09 pm   #2
Simon Gittins
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Default Re: Roberts R200

There's nothing to lose by cutting the screen leads as a test as per Post 2:

Yes, the AF12x are known good replacements.
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Old 26th Nov 2023, 8:58 pm   #3
David G4EBT
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Location: Cottingham, East Yorkshire, UK.
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Default Re: Roberts R200

Firstly, there are two version of the data - one for sets with serial numbers up to 7000, then one from 7001 onwards, so it's worth checking your serial No. (Both datasheets are available from top RH of the page if you don't have them). There were modifications from serial numbers 85,690, and 90,000, mentioned in the data.

Before you do anything, I'd suggest you first check the current consumption, (meter on mA range in series with battery), which should be approx 12 mA with no sigs tuned in, and 20mA with a station tuned in. If it's much more than that referring to the post 7001 ERT Sheet 1412, the likely cause will be either C29 (100uF) and/or C24 (100uF) which, if leaky, will pass current from the -ve line to ground. The R200 dates from 1963, so the electrolytics are now 60 years old and way past their 'mean time before failure'.

Then check the voltages around the radio as compared to thee circuit to see if any anomalies are apparent.

Don't assume that the fault lies with the AF117s in the earlier stages. It's worth snipping the screens anyway, but often in a dead R200/R300 (etc), it's the detector diode which has failed. Ideally you need a signal tracer/injector to see if that is so. (Velleman K7000 or whatever). If you inject a signal at the slider of the volume control, (or even scratch it with a screwdriver), and hear a loud tone from the speaker (or scratching noise), that suggests the audio stage is working.

The detector diode (X2 - OA90), is hidden in the case of IFT3. If you apply the probe if a signal tracer to the volume control and hear no tuneable signals, put the injector probe on the collector of TR3. If you hear signals there, that points to a dead X2. (A suitable replacement is the 1N34A - widely and cheaply available on eBay etc).

If no sigs at the collector of TR3, try at the base, then do likewise at TR2, and TR1 to narrow down which stage is faulty.

Just a few off the top suggestions which I hope might help.

Good luck with it.
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Old 26th Nov 2023, 11:19 pm   #4
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Location: Thetford, Norfolk, UK.
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Default Re: Roberts R200

Excellent advice from David, but in answer to your question, I do have experience of replacing the AF117's with AF12x transistors, usually AF124's. I used to 'blast' the whiskers away on AF117's with good success, but have taken to replacing them now, mainly due to finding AF117's inside difficult to access cans on some other models.

Regarding AF12x's....

Pros - fixes the problem that is caused by AF117s while still using a germanium device. No re-biasing required. Super close match spec wise, indeed I believe the devices were actually the same just in different packages. Still has that 'germanium sound' that some people including me believe sounds nicer.

Cons - can be awkward to fit as the lead out is different and AF12x devices have much shorter leads. Expensive.
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Old 27th Nov 2023, 12:20 am   #5
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Location: Fakenham, Norfolk, UK.
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Default Re: Roberts R200

Originally Posted by David G4EBT View Post
Firstly, there are two version of the data - one for sets with serial numbers up to 7000, then one from 7001 onwards, so it's worth checking your serial No.
If I remember rightly the main change to the board at serial 70001 introduced the AF117s, so this set (almost) has to be of the later version. Seemed worth mentioning as occasionally the serial number plate is missing.

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