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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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1st Oct 2017, 3:26 pm | #1 |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
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Roberts R606 MB
Hello everyone,
I have just returned from the Audio Jumble in Tonbridge and I am now the proud owner of a Roberts R606 MB that cost me a pound! Needlessly to say it has problems, it's dead, and I would like a little help. So far I have most of the major diagrams but none of the PSU stage - can anyone help me with this? When plugged in I can hear a slight mains hum from the transformer but no clicks or other audio from the loud speaker. The set is in nice condition and is only missing trim from the tuning knob and band select buttons which, hint, would also be nice to get hold of. Any help would be most appreciated. |
1st Oct 2017, 3:47 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
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Re: Roberts R606 MB
The first thing you need to do is determine which version of the MB you have. It started off as just a 606 with a mains PSU, but this design was replaced quite quickly with a completely different one. The early models have Ge output transistors like the 606, while the later ones use a BC464/5 Lockfit Si pair.
Check the earphone socket switching before looking elsewhere. These radios suffer a lot of Lockfit transistor problems but these are cheap and easy to substitute. I would use batteries or a bench supply for initial testing. The mains PSU is a separate subsystem on the battery holder. |
1st Oct 2017, 3:49 pm | #3 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,428
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Re: Roberts R606 MB
If there is an earphone socket they can cause no sound. Also worth trying batteries before delving into the PSU.
Edit, crossed with Paul, at least we both have heard of the earphone socket causing problems.
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Frank |
1st Oct 2017, 5:04 pm | #4 | |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
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Re: Roberts R606 MB
Quote:
I had to scratch my head for a moment when you mentioned Lockfit Transistors and then they came back to me!! Fine with the Ge and Si versions and hopefully mine will be the mostly Si version. The diagrams that I have aren't complete but they do show two transistors with a zener diode and a 14V feed - presumably, excluding the rectifier and caps, that is the DC part of the mains regulator? |
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1st Oct 2017, 5:15 pm | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
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Re: Roberts R606 MB
From memory it's a fairly basic 9V stabilised supply. It dates from before mass market linear regulators so uses a zener and a modest power transistor. I've never known one develop an electronic fault, but the switchery on the mains socket can give problems.
For a good summary of the general Lockfit issues, see here: https://www.markhennessy.co.uk/artic...ransistors.htm |
2nd Oct 2017, 6:36 pm | #6 |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
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Re: Roberts R606 MB
To cut a short story even shorter - it was the on/off switch open circuit and I was lucky enough to be able to use the other pair of unused contacts on the same switch.
And it sounds VERY nice indeed. The power supply board has lost the two securing star? washers. The tiny little pieces of plastic at the top of the post have snapped off so they will not lock into place any more - has anyone overcome this situation? I have included a picture of the board for you to look at. Cheers John |
2nd Oct 2017, 7:38 pm | #7 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,193
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Re: Roberts R606 MB
Two blobs of silicone sealant? Not too difficult to take apart if the need arises.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
2nd Oct 2017, 7:45 pm | #8 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,788
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Re: Roberts R606 MB
Hot melt glue?
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2nd Oct 2017, 8:01 pm | #9 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
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Re: Roberts R606 MB
If the excellent advice above does not point to the fault on your particular set the incomplete diagram below may help as it includes the power supply section and audio for the later version.
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2nd Oct 2017, 8:03 pm | #10 |
Hexode
Join Date: Aug 2014
Location: Dartford, Kent, UK.
Posts: 435
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Re: Roberts R606 MB
Yes, both ideas would allow for the washers to be replaced - although I have just used blue tac as a temporary measure.
I am listening to it at the moment while trying to clean years of 'sticky stuff' from it. Now all I have to do is try and find the caps for the wave band buttons and tuning knob. Thanks once again for your help. |