Roberts R200 capacitors

[Carole Jarvis]

Hi, First post on this sight so please be gentle
I have a Roberts R200 serial number 74741 which I'm trying to bring back to life.
I have tinkered with DAB radios in the past but found this and just had to have a go at saving it from the scrap heap.
I gave done the usual put some power through and got nothing so tested a few point and power was getting in. Tapped the transistors and di get a scratchy noise at one end bot nothing else so have ordered some transistors which are on the way.
I then moved on to the capacitors as they are bound to be as good as dead at there age.
This is when I came upon a few problems so I did some research and found quite a few good youtube videos but the one ting I could not find out is where to get hold of replacement (I understand that they would have to be modern replacements) but I just can't find some of them with the correct Voltage/uf ratings? Can anyone help me with identifying the correct replacements? So far the only one I have found is a 10v 100uf replacement but the 6v 10uf just aren't out there as far as I can see?

Can anyone help me please?

Carole

[VT FUSE]

You don’t say if axial or radial leads but you should find plenty rated at 16V, 25V, 35V & 50V.
I try to get as close as per original with low Voltage applications such as your radio as there is a need for a certain Voltage to maintain the forming of the foil insulation layer and some dim memory says not to fit a much higher Volt rating as the foil might never properly form its insulating layer.
You may need to get inventive in fitting replacements as you will find many radial leaded whereas you might be replacing an axial type.

And welcome to the forum! You will find everyone to be friendly and will try to help- even the night
Owls that inhabit it.

Mike.

[Graham G3ZVT]

Hi Carol,
As your instinct was to give the transistors a good tap, I presume you already know about the tin-whisker phenomenon, but be aware it's age rather than usage related, so if you've ordered more old-stock AF117s, they are just as likley to be bad too, not to mention being very "rare" & expensive.

[Nuvistor]

Doesn’t the R200 use the OC range of transistors that don’t have the tin whisker problem?
A circuit and some voltage readings would be better that just replacing components adhoc.

[Graham G3ZVT]

I think after S/N 70,000 they changed to AFs, and Carole helpfully gave us the serial number.
There's a sporting chance the set would spring back to life by snipping the screen lead of the transistor that makes a noise in the speaker when tapped.

[Carole Jarvis]

Thank you all for your replies.
I have managed to get some transistors from China that should fit the bill however it's the capacitors that are a problem, I have found some 10v 100uf ones that should be UK but it's the 6v 10uf that are the problem.
Anything at 10uf seems to be around the 100v range?
There are five capacitors in the set and they are the red plastic type with a yellow film around them.
I have seen someone open them up and scrape out the contents so that can fit over the new capacitors keeping the original look the the radio.
Another problem I have is that the control knos screws just will not budge to get them off any tips on that as well?

[Graham G3ZVT]

I'm surprised you haven't found 10uF 16v capacitors they are very common, and ideal to replace 10v ones.

Yes, some of us would re-stuff the original Plessey caps with new components, but as Shakespeare wrote "That way madness lies"

[VT FUSE]

I am intrigued to hear more about transistors from China for this radio? My experience is that the R200 is firmly of Germanium technology and have only seen Silicon types advertised by Chinese sellers.
Mike.

[Carole Jarvis]

I'm not sure they will be the best choice or that they will even work but they are worth a try at the price?
I have put the link bellow (I hope that is OK and withing the rules?)

https://www.aliexpress.com/item/1005007183443343.html?spm=a2....order_detail_item.4.7896f19c0aJrIw

[Carole Jarvis]

Originally Posted by Graham G3ZVT

I'm surprised you haven't found 10uF 16v capacitors they are very common, & ideal to replace 10v ones.

Yes, some of us would re-stuff the original Plessey caps with new components,
but as Shakespeare wrote "That way madness lies"

Will the extra 6 volts be OK?

[Uncle Bulgaria]

It's always a good idea to track down the fault before changing components willy nilly. If AF117s then there is a wealth of information on this forum about their known issues. Once you have some sound then you can go through the service manual and check what might need changing. You can find a manual here.

[David G4EBT]

Originally Posted by Graham G3ZVT

I'm surprised you haven't found 10uF 16v capacitors they are very common, & ideal to replace 10v ones.

Yes, some of us would re-stuff the original Plessey caps with new components,
but as Shakespeare wrote "That way madness lies"

Switch Electronics (a top notch family firm run by three triplets!) can supply all the radial lead electrolytic capacitors that you need.

IE:
C11 10uF
C20 100uF
C21 2.2uF
C22 100uF
C24 47uF

The minimum order quantity is five of each value, which, at 7p each including VAT, won't break the bank.

https://www.switchelectronics.co.uk/collections/electrolytic...AxlsOHUJgO4FhrdIj8LB_3SKeySaQfQKuWA

Homepage: https://www.switchelectronics.co.uk

As to the excessive current consumption, as has been said, the decoupling electrolytics will almost certainly be the culprit. With any transistor radio of this era (1960) - Roberts, Bush, etc, whether working or not, the first thing to do is the check the current consumption. In this case - the Roberts R200 - C24 for example in basically in parallel with the battery, and if leaky (it will be after 65 years), can near enough put a dead short across it.

The easiest way to check the current consumption is to leave the radio switched off, then with a multi-meter on the mA range, put the two probes across the switch contacts, which will allow the current to flow through the meter and turn the radio on. (See Pic).

Good luck with the restoration.

[Maarten]

Originally Posted by VT FUSE

You don’t say if axial or radial leads but you should find plenty rated at 16V, 25V, 35V & 50V.
I try to get as close as per original with low Voltage applications such as your radio as there is a need for a certain Voltage to maintain the forming of the foil insulation layer and some dim memory says not to fit a much higher Volt rating as the foil might never properly form its insulating layer.

The oxide layer is already formed, but in order for it to stay in shape optimally, it needs to see a DC bias between 20% and 80% of its nominal working voltage. 10% to 90% is still acceptable, but may already cause increased wear.

In practice, using a 50V miniature capacitor (as most low values aren't easily available in lower working voltages) in a 9V battery set is acceptable. It will last for years even if used at almost no bias voltage, anyway. Life below 10% bias voltage would be comparable to the normal shelf life of an unused capacitor.

[VT FUSE]

Thanks Maarten
Always happy to be corrected, I have used plenty of 63V rated electrolytics at very low Voltages Round 6-12V which confirms what you say.
Mike.

[paulsherwin]

Originally Posted by Carole Jarvis

I'm not sure they will be the best choice or that they will even work but they are worth a try at the price?
I have put the link bellow (I hope that is OK and withing the rules?)

https://www.aliexpress.com/item/1005007183443343.html?spm=a2....order_detail_item.4.7896f19c0aJrIw

If all is as it appears then they should be OK. These are early 60s transistors which won't have been manufactured by mainstream manufacturers for decades. I'd be astonished if they've ever been made in China let alone in the last few years. I use AliExpress myself, but their sellers are notorious for dishonest or misleading descriptions and indeed downright fraud. You have to be very wary.

However, now you've placed the order it will be interesting to see what turns up. Please let us know the outcome, whether good or bad.

The good news is that the R200 is extremely tolerant of transistor types, and a huge range will work as AF11x replacements, even dirt cheap jellybean silicon types.

You can fit capacitors with higher voltage ratings than the originals, but not lower. The rating is just the voltage above which they're likely to go bang (but see post #13).

[Carole Jarvis]

Originally Posted by David G4EBT

Switch Electronics (a top notch family firm run by three triplets!) can supply all the radial lead electrolytic capacitors that you need.

IE:
C11 10uF
C20 100uF
C21 2.2uF
C22 100uF
C24 47uF

The minimum order quantity is five of each value, which, at 7p each including VAT, won't break the bank.

https://www.switchelectronics.co.uk/collections/electrolytic...AxlsOHUJgO4FhrdIj8LB_3SKeySaQfQKuWA

Homepage: https://www.switchelectronics.co.uk

As to the excessive current consumption, as has been said, the decoupling electrolytics will almost certainly be the culprit. With any transistor radio of this era (1960) - Roberts, Bush, etc, whether working or not, the first thing to do is the check the current consumption. In this case - the Roberts R200 - C24 for example in basically in parallel with the battery, and if leaky (it will be after 65 years), can near enough put a dead short across it.

The easiest way to check the current consumption is to leave the radio switched off, then with a multi-meter on the mA range, put the two probes across the switch contacts, which will allow the current to flow through the meter and turn the radio on. (See Pic).

Good luck with the restoration.

Thank you David I have already put them on my list (I have a dream shopping list already - Christmas is coming )

Originally Posted by paulsherwin

If all is as it appears then they should be OK. These are early 60s transistors which won't have been manufactured by mainstream manufacturers for decades. I'd be astonished if they've ever been made in China let alone in the last few years. I use AliExpress myself, but their sellers are notorious for dishonest or misleading descriptions and indeed downright fraud. You have to be very wary.

However, now you've placed the order it will be interesting to see what turns up. Please let us know the outcome, whether good or bad.

The good news is that the R200 is extremely tolerant of transistor types, and a huge range will work as AF11x replacements, even dirt cheap jellybean silicon types.

You can fit capacitors with higher voltage ratings than the originals, but not lower. The rating is just the voltage above which they're likely to go bang (but see post #13).

Keeping my fingers crossed but they won't break the bank either way

Originally Posted by paulsherwin

If all is as it appears then they should be OK. These are early 60s transistors which won't have been manufactured by mainstream manufacturers for decades. I'd be astonished if they've ever been made in China let alone in the last few years. I use AliExpress myself, but their sellers are notorious for dishonest or misleading descriptions and indeed downright fraud. You have to be very wary.

However, now you've placed the order it will be interesting to see what turns up. Please let us know the outcome, whether good or bad.

The good news is that the R200 is extremely tolerant of transistor types, and a huge range will work as AF11x replacements, even dirt cheap jellybean silicon types.

You can fit capacitors with higher voltage ratings than the originals, but not lower. The rating is just the voltage above which they're likely to go bang (but see post #13).

I will let you know how I get on when they arrive fingers crossed

Once again guys load of help and advice, I will go away now and do some more research before I jump in with two feet.
I have to say though that my first experience with Vintage-radio has bean far better than with other 'interest' sites that have used.
Just a warning though.... After I get this radio finished I have loads of more modern radios under my desk mostly DAB but some Hi-Fi one too

[David G4EBT]

You explained at the outset that your R200 was serial number 74741, and as Graham said in posts #3 & 5 said, from serial No 70000 the updated circuit use AF117 transistors for Tr1,2, and 3. It differs in other respects too. Though it's tempting to assume that the AF117 transistors have developed 'tin whiskers' leading to a dead set, while that often turns out to be correct, it's better to ascertain that through diagnosis - not just by replacing them.

Ideally, if you want to get into restoring transistor radios, to help speedy diagnosis, a signal tracer/injector helps greatly.

If you apply a signal injector probe to the volume control and hear a tone, that shows the audio stage is working. If you then apply the injector probe to the collector of TR3 and hear nothing, that points to a defective detector diode, which is a common fault often overlooked on Roberts and Bush radios of this era. Rather inconveniently in this version of the R200 with square rather than round oscillator and IFTs cans, the diode ('X2' - OA90) is hidden inside the IFT3. If it fails, while the frequency changer, and IF stages may be fine, and so might the AF stage, the radio will appear dead. A commonplace 1N34 germanium diode will be fine as a replacement. (There are two other diodes in this version or the R200 - 'X1', an OA79, and X3, which is actually an OC78 transistor connected as a diode).

With a signal tracer with the probe on TR3 collector and hear tuneable signals, that would show that the frequency changer and IF stages are working. If you hear nothing, you can listen for signals with the signal tracer probe at the collector and base of TR3, TR2 and TR1. That will help pinpoint where the fault lies without (perhaps needlessly), de-soldering transistors and risking damage to the PCB.

There have been lots of threads on the forum, and countless YouTube videos on signal injecting and tracing, with the Velleman K7000 injector tracer kit being popular:

https://www.vintage-radio.net/forum/showthread.php?t=138951

The kit is widely available from many suppliers such as ESR Electronics, where it presently costs £10.80.

https://www.esr.co.uk/velleman/products/frame_kits.htm

Building that or any other such tracer/injector might seem like a distraction from restoring your R200, as indeed it is, but simply chasing elusive faults by subjective guesswork rather than methodical diagnosis, hoping to get lucky can be very dispiriting, and it's a well trodden path along which many of us have ventured.

The AF stage can at least be checked without a signal injector just by scratching the slider of the volume control which should produce a loud scratching noise in the speaker.

Before you do anything, a good idea would be to check the voltages as compared with the circuit. With a fresh battery, you should see 8.75V at the collector of TR5. If it's less than that, it would confirm that C29 (across the battery on the circuit) is passing DC current and pulling the voltage down. In any event, the electrolytics will need replacing. Do use a solder sucker or de-soldering braid and don't allow the iron to 'loiter' on the joints as the tracks on the Paxolin printed circuit board lift so easily and get damaged.

The numbering I gave for the electrolytic capacitors was for the earlier version.

The numbering for this later version is:
C16: 10uF
C24: 100uF
C26: 2 uF (2.2uF nowadays).
C27: 100uF
C29: 100uF

The attached pic shows the location of the detector diode, hidden away.

Hope these additional comments might be of help.

Good luck.

[Carole Jarvis]

Thank you David this is going to be a great help and looking forward to building my signal injector.
I'm getting to be a bit of a dab hand at soldering a steady hand helps. I do a bit of watch cleaning and small repairs, I find it somehow relaxing and so satisfying when works It does have it's downs as well but the successes make up fer them.
Anyway load to look into and work to be done so thank you again

Carole

[Uncle Bulgaria]

As ever David has covered everything comprehensively. I'll just put in another vote for a solder sucker and some solder braid (or 'wick') in a couple of different sizes. A pot of flux really helps the braid to remove the last vestiges of old solder, and spreads the heat. When removing known broken components it can be helpful to snip the leads close to the board, grip the lead remnant with pliers then apply the iron to the board/lead junction. The lead is quickly removed as soon as the solder melts sufficiently, minimising damage. A sucker can then clean the hole, especially if it can be applied from one side and the iron from the other (a 'helping hand' clamp is handy - ha! - here). Some suckers and braid are here. I like using a tin of hard flux paste which can be melted into solder braid easily for added efficacy. This sort of thing.

Indeed it is very easy to damage the tracks on the board. One of the many reasons a lot of members here are keen to minimise component changing before comprehensive non-destructive measurements have been taken.