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Old 21st Nov 2021, 8:47 pm   #1
6SN7WGTB
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Default Roberts R300 - replace electrolytics?

I have just acquired one of the above. Initially I thought it was an R200 Mk 3, but it's not - being a R300.

It was reported as 'dead' but the click when turning on showed this not quite the case. Injecting a signal into the wiper of the volume control showed the audio to be fine.

It's an AF117 model, and all measuring the EBC voltages showed that all three were faulty.

When extracted all showed either dead shorts or other than infinite resistance between shield/case and other terminals.

I have got AF124 or OC169s I could use, but for entertainment zapped all three AF117s.

I then did a full alignment and it works well, or at least as well as modern household RF interference will allow. On the strong stations it's clear and clean.

I wouldn't normally turn something on with 60 year old elecs, but with this being 9V I did and seem to have arrived at a working set.

So, a long preamble, but my question is - should I replace the electrolytics?
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Old 21st Nov 2021, 8:56 pm   #2
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Default Re: Roberts R300 - replace electrolytics?

If the electrolytics are the Plessey type with red-and-black plastic ends and a yellow label round the middle - yes, replace: they lose capacitance and/or go leaky.

If they're the Philips-Mullard type with an aluminium can and a light-blue transparent insulating sheath - I'd say not to bother with replacement unless there are obvious issues.
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Old 21st Nov 2021, 9:04 pm   #3
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Default Re: Roberts R300 - replace electrolytics?

Oh

They are 100% red and blacks. ELKOMOLD branded.
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Old 22nd Nov 2021, 7:57 am   #4
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Default Re: Roberts R300 - replace electrolytics?

Looking again, and for perhaps the benefit of all, mine are per the populated photo below.

So, yes, they are black with red ends but not 'red and black ends with yellow label' = per the single pic.

I do believe they are still TCC Plessey though, so the advice remains the same?
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Old 22nd Nov 2021, 8:00 am   #5
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Default Re: Roberts R300 - replace electrolytics?

Change 'em! They're notoriously unreliable.
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Old 22nd Nov 2021, 8:03 am   #6
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Default Re: Roberts R300 - replace electrolytics?

I think it depends what your plans for it are.

If you intend to keep it yourself, then why bother messing around and spoiling its originality if it works? Ultimately, failure of these caps is likely to do nothing more than degrade performance or increase battery consumption. If this happens, you can fix it later.

OTOH, if you're planning to sell it with any kind of guarantee...

You could also argue that changing them is likely to improve reliability and therefore reduce the risk of future custodians writing it off as "broken" and throwing it away.
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Old 22nd Nov 2021, 8:22 am   #7
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Default Re: Roberts R300 - replace electrolytics?

I have several early Roberts sets, all work fine with original caps in place.
None are drawing excess current, I would replace the AF117's though, zapping them usually brings them back to life, but they will fail again once the whiskers regrow.


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Old 22nd Nov 2021, 8:55 am   #8
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Default Re: Roberts R300 - replace electrolytics?

It's a keeper so I'm inclined to leave as is.

I suppose I am a bit curious as to whether it would be better recapped, as I do like everything to work as it should, even at the expense of appearance.

My plans for the AF117s would be to 're-can' them (AC125 inside) when they fail again else eventually I'm risking lifting the PCB tracks with repeated pseudo-repairs - and which I acknowledge are fairly temporary.

Were I to move it on, other than to someone in the know who would like to decide on originality vs. operation, I would indeed 'fix' it all to the best of my ability.
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Old 22nd Nov 2021, 9:30 am   #9
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Default Re: Roberts R300 - replace electrolytics?

I'd keep it as original as possible, so only defective electrolytics get replaced. I'd even experiment on it. Take a note of after which time the whiskers have grown back, and then try another method such as melting them by putting the soldering iron to the case for a short time. See which fix lasts the longest.
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Old 22nd Nov 2021, 12:22 pm   #10
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Default Re: Roberts R300 - replace electrolytics?

I have a TR82 with the original electrolytics still in place. Same type as yours. The ESR readings are awful but replacing them makes no discernible difference to the performance so I have kept the old ones in the set for originality.

I've also zapped the tin whiskers rather than replace the AF117s, again in the name of originality, and who cares if I need to do it again in the future? Its a hobby, I'll get the satisfaction a second time.
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