Roberts RT22 - Capacitors - UK Vintage Radio Repair and Restoration Discussion Forum

simonbt · 8th Sep 2019, 9:11 pm

Hi

I'm really a beginner here. I have quite a few vintage radios mostly working so it's time to embark on some repairs.

I have a Roberts RT22 which I dismantled to clean but some of the Mullard (?) capacitors (C20 and C39) ends were in the case, looks like they have started to split/ crack.

I have the service manual and these state 100nF for both. RadioCruncher (Graham) said these would now be 0.1uF / 104?

I have had a look on Ebay and was just wondering what voltage these should be as there are differing voltages for these, anything from 100V to 630V (it doesn't state in the service manual) The radio is 9v / PP9 - no mains.

thanks

Simon

nutteronthebus · 9th Sep 2019, 9:24 am

This is a late 70's early 80's radio and 25v caps is all it needs try RS for spares and if you have problems I only live in Glossop and am willing to help

Dave

simonbt · 10th Sep 2019, 8:49 pm

Thanks Dave. I've been to Glossop quite a lot recently. You don't offer lessons do you...

I would love to start fault finding and repairing as buying 'repair only' would be so much cheaper and I'm keen to start this as a hobby plus I have loads of stuff here that just doesn't work and really needs to be working, both radios and old computers etc.

I've had a look on RS and closest I can find is KEMET 100nF MLCC 50V dc which I am hoping is close enough.

Thanks for your help - I really appreciate it.

paulsherwin · 10th Sep 2019, 9:34 pm

As a general rule, with transistor gear you only need capacitors rated at the supply voltage plus a bit of headroom, so 12V will be fine in this case. Higher voltage ratings will do no harm. You often can't find low value caps rated below 50V because it costs just as much to make them for lower max voltages.

simonbt · 11th Sep 2019, 7:56 am

Ahh I see Paul, Makes sense. You're right though - I can't find any low voltage caps at all...well not as low as the 12V you mentioned.

David G4EBT · 11th Sep 2019, 8:41 am

Quote:

Originally Posted by simonbt

Hi

I'm really a beginner here. I have quite a few vintage radios mostly working so it's time to embark on some repairs.

I have a Roberts RT22 which I dismantled to clean but some of the Mullard (?) capacitors (C20 and C39) ends were in the case, looks like they have started to split/ crack.

I have the service manual and these state 100nF for both. RadioCruncher (Graham) said these would now be 0.1uF / 104?

Simon

Firstly, 100nF, 0.1uF and 104 are all the same capacitance value expressed in different ways, just as one foot can be expressed as twelve inches. You'll see all of those terms used on capacitors, on websites and in service data. As the capacitors on your radio are fitted to a printed circuit board, ideally, the 'pitch' of the leads (the space between each wire end) should be the same - probably 10mm, but it doesn't matter if the pitch of the capacitors is 5mm - you can bend the wire ends so that they match the position of the holes. (Almost all modern capacitors including electrolytic ones, and resistors too, are physically smaller than those of yesteryear due to improvements in materials and manufacturing techniques).

There is a variety of materials used - ceramic disc, mylar etc, some of which I've given listings for below. Looking at the position of C20 and C39 on the diagram of the PCB, I'd have thought that the mylar ones would probably be a good choice, but any would suffice. Capacitors are so cheap that whether you buy them from eBay of say RS, Farnell, Crickelwood ESR electronics or whoever, you'll probably find that they have a minimum order level - maybe five, ten or twenty. 100nF is a useful value to have - they're used extensively.

I'm not suggesting that you use any of the suppliers below in preference to the likes of RS, but they're all UK based suppliers with good feedback and the prices shown are post free:

Ten Ceramic disc: 50V:

https://www.ebay.co.uk/itm/100nF-0-1...U2h8ezmzAPW6gQ

25 Ceramic monolithic: 50V:

https://www.ebay.co.uk/itm/Ceramic-C....c100005.m1851

20 Mylar polyester 100V:

https://www.ebay.co.uk/itm/100nF-Aud....c100005.m1851

Ten Axial multilayer ceramic 50V:

https://www.ebay.co.uk/itm/AVX-50V-0....c100005.m1851

Hope that helps a bit Simon.

Best wishes on your endeavours.

simonbt · 13th Sep 2019, 9:58 pm

That's great David, that's really helpful. Call me daft but I thought I would have to buy something similar to the size/shape that are in now but seems not!

I'll go along with your recommendation and start to get a selection of components together will will save me in the long run.

Many thanks

8th Sep 2019, 9:11 pm	#1
simonbt Triode Join Date: Feb 2016 Location: Manchester, UK. Posts: 24	Roberts RT22 - Capacitors Hi I'm really a beginner here. I have quite a few vintage radios mostly working so it's time to embark on some repairs. I have a Roberts RT22 which I dismantled to clean but some of the Mullard (?) capacitors (C20 and C39) ends were in the case, looks like they have started to split/ crack. I have the service manual and these state 100nF for both. RadioCruncher (Graham) said these would now be 0.1uF / 104? I have had a look on Ebay and was just wondering what voltage these should be as there are differing voltages for these, anything from 100V to 630V (it doesn't state in the service manual) The radio is 9v / PP9 - no mains. thanks Simon

9th Sep 2019, 9:24 am	#2
nutteronthebus Hexode Join Date: Jun 2011 Location: Glossop, Derbyshire, UK. Posts: 487	Re: Roberts RT22 - Capacitors This is a late 70's early 80's radio and 25v caps is all it needs try RS for spares and if you have problems I only live in Glossop and am willing to help Dave __________________ Any tool can be used as a hammer but a screwdriver makes the best chisel

10th Sep 2019, 8:49 pm	#3
simonbt Triode Join Date: Feb 2016 Location: Manchester, UK. Posts: 24	Re: Roberts RT22 - Capacitors Thanks Dave. I've been to Glossop quite a lot recently. You don't offer lessons do you... I would love to start fault finding and repairing as buying 'repair only' would be so much cheaper and I'm keen to start this as a hobby plus I have loads of stuff here that just doesn't work and really needs to be working, both radios and old computers etc. I've had a look on RS and closest I can find is KEMET 100nF MLCC 50V dc which I am hoping is close enough. Thanks for your help - I really appreciate it.

10th Sep 2019, 9:34 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Roberts RT22 - Capacitors As a general rule, with transistor gear you only need capacitors rated at the supply voltage plus a bit of headroom, so 12V will be fine in this case. Higher voltage ratings will do no harm. You often can't find low value caps rated below 50V because it costs just as much to make them for lower max voltages.

11th Sep 2019, 7:56 am	#5
simonbt Triode Join Date: Feb 2016 Location: Manchester, UK. Posts: 24	Re: Roberts RT22 - Capacitors Ahh I see Paul, Makes sense. You're right though - I can't find any low voltage caps at all...well not as low as the 12V you mentioned.

13th Sep 2019, 9:58 pm	#7
simonbt Triode Join Date: Feb 2016 Location: Manchester, UK. Posts: 24	Re: Roberts RT22 - Capacitors That's great David, that's really helpful. Call me daft but I thought I would have to buy something similar to the size/shape that are in now but seems not! I'll go along with your recommendation and start to get a selection of components together will will save me in the long run. Many thanks