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Old 24th Apr 2013, 9:11 am   #1
sobell1980
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Default Roberts RMB Problems

Hi all.
Finally put the rmb back into its case after having it working on the bench for days out of it's case. Put it altogether last night and it was working beautifully, then it cut out. I found by fiddling with the frame aerial extension socket/connections that it would work again. While it was working i fiddled with the socket again and it stopped working again. The ext socket for the aerial are connections a and e on the data sheet. Surely these just being an extension to the mw aerial they shouldnt stop it receiving? I have unscrewed connector a and e and the lower connection of the actual socket where the wire passes through the wooden frame looks corroded and powdery. Would this be causing the issue ?
Many thanks as always.

Forgot to say this also affects lw operation when this poor frame socket connection happens, not just on mw. When i wiggle socket a and e and it works i regain both lw and mw. When i wiggle it again and it cuts out, both lw and mw are lost . Always appreciate your advice and help.
Dave.
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Old 24th Apr 2013, 9:54 am   #2
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Hi Dave,

Glad you're nearly there.

I think you've hit the nail on the head. Mine's just the same sometimes - I suspect fumes from the batteries cause odd corrosion here and there in these.

You could replace the flexible wiring and hard-wire to avoid those pesky connectors once and for all if you wanted.

I seem to remember the frame aerial forms an integral part of a tuned circuit, which explains why you get no results at all when it's disconnected.

N.
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Old 24th Apr 2013, 9:58 am   #3
G0HFCFrank
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

I'm not familiar with this set but looking at the circuit, if the frame aerial is the physical coils L1 and L2 then they make up a parallel tuned circuit with C34 so any bad connection in this area would affect the signal input. I would clean the whole lot up and treat the connections to a touch of vaseline.
Frank C.
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Old 24th Apr 2013, 10:36 am   #4
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Hi Nick
yes, as i close the back door, the two socket connections from the back door with the two small pieces of wire from socket to frame aerial move. This causes said problem as the door is opened and closed. I think the problem is where the wire passes through the wooden frame aerial from the socket. It does work with the two wires from the back door to the frame aerial disconnected. It is where these two wires from the back door push into the sockets on frame aerial i think is the issue. These just seem to act as an extension piece to the socket on the back door. So you think i should hard wire frame aerial socket to back door and make sure frame aerial is good with a resiatance check?

Hope i made sense?
Dave
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Old 24th Apr 2013, 10:53 am   #5
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Yes, I think I get what you're saying, but I haven't got my RMB to hand to help me.

Resistance checks are the way to go. You should be able to establish what's going open-circuit and where quite easily. If you've got a meter with a bleepy continuity tester and crocodile clips, it would be very simple to do.

N.
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Old 24th Apr 2013, 9:54 pm   #6
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Hi all,

Got round to having a look this evening. Ive repaired the mw frame aerial extension lead connections which are now secure and soldered and check out with a continuity test. All went well for half an hour or so then faded out again! Valve 4 seems to have a poor connection on its base. When removed and tilted on an angle, when re fitted it then all works again so obviously it is the valve base. i have already replaced valve 2 base/ socket for exactly the same problem. I just wish this had reared it's ugly head before putting back into the cabinet. Would valve 4 socket/ base be the same part as i have previously replaced for valve 2 ? One kind member here previously posted my last replacement and was wondering if anyone could kindly help me out again, or advise the part number and where i could purchase one? Do you think while i have the chassis removed for the last time it would be worth replacing all the valve sockets? Look forwards to hearing from you.

Many thanks,
Dave.
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Old 27th Apr 2013, 10:56 pm   #7
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

That sounds like a lot of work though, Dave.

Have you scraped the pins of the valve clean with a sharp blade, and slightly re-tensioned the connections in the valve base by closing them a tiny bit?

N.
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Old 28th Apr 2013, 11:29 am   #8
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Hi Nick

i have scraped valve pins clean and sprayed cleaner into valve socket and worked the valve in and out to help clean. It works a little longer then gives out. Adjustment of the valve in its holder bringsvthe set back to life. How can i retension? It looks very fiddly to do this.is there an easy way to do this? The pins are recessed so look difficult to even get on with the chassis in situe? Many thanks.
Dave.
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Old 28th Apr 2013, 12:02 pm   #9
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Hi Dave,

There's no easy way, I'm afraid. I just use a big needle, but as you say, it may need to be done from the other side of the chassis.

N.
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Old 28th Apr 2013, 3:07 pm   #10
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Hi Nick,

had a go tensioning with a strong needle, pushing the valve in and out several times and tensioning again without removing chassis. Been playing 3 hours now, no problems so far. maybe also the sharp needle scratched the pins internally to aid a good connection as well as the tensioning.
Many thanks for your help throughout this project and following my journey on this rmb that was totally dead when i bought it.

Regards
Dave.
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Old 28th Apr 2013, 3:27 pm   #11
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

That's great, Dave, hope it lasts(!).

Nick.
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Old 29th Apr 2013, 6:52 am   #12
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

It lasted 5 hrs. Another fiddle with valve 4 in it's socket made it work again and then kept cutting out. It looks like the pins of the socket only hold their tension briefly and are obviously worn out. Looks like it will be coming apart again!
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Old 21st Feb 2014, 9:44 pm   #13
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Finally got this set back on the bench after completing a Hacker herald inbetween (i needed the break from it). Found myself starting lots of different sets and not completing them. So it's time to face the RMB again with the dreaded valve socket issue. I have decided to get the chassis back out and replace all the valve sockets as i really do not want to be replacing another socket to find anothe one fail later. If it suffered with corrosion from battery fumes then i fear they may all have suffered the same fate. They have outlasted their life expectancy anyway and are the cheap paxolin type i believe. I also do not want to damage the valves by handling them and tipping them in their sockets to get it to work. Anyway this is the update with this set and the chassis will be coming out over the weekend. I will keep you posted with progress. Any ideas of a good b7g socket supplier?
Regards
Dave.
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Old 21st Feb 2014, 9:59 pm   #14
60 oldjohn
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Just a thought have you changed the valve? some of the early valves are prone to the wire breaking inside the valve pins, giving intermittent results.

John.
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Old 21st Feb 2014, 10:13 pm   #15
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

The set is now totally dead with no amount of valve 4 wiggling bringing the set back to life.Valve socket 2 suffered the same fate too. It did appear to make an improvement briefly with the pin tensioning and cleaning but now nothing at all. The valve also feels a very vague fit in the socket, not a positive feel and with the valves mounted horizontally in the chassis,valve 4 could almost tip over under its own weight. Some of the other valve sockets feel the same but not as bad. I do feel this is the common denominator but is there anyway to test the valve as i do not have a replacement to hand or a valve tester.

Last edited by sobell1980; 21st Feb 2014 at 10:16 pm. Reason: spelling
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Old 22nd Feb 2014, 2:12 pm   #16
60 oldjohn
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

I don't think there is a simple way, other than swapping out valves from a known good set. I hope you are able to find someone in your area with a valve tester willing to help.

John.
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Old 22nd Feb 2014, 5:32 pm   #17
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Default Re: Roberts rmb finally finished but poor intermittant aerial connection.

Any one local to me kind enough to test this out for me? The sockets feel awful and loose, but to test the valve as well would put my mind at rest. I am certain pushing the valve in it should feel firmer than it does. Many thanks as always

Dave.
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Old 22nd Mar 2014, 5:40 pm   #18
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Default Re: Roberts RMB finally finished but poor intermittent aerial connection.

Hi all,

Finally got the chassis out this afternoon to find the B7G sockets i had ordered from ebay to be totally the wrong size! The socket falls through the hole in the chassis and the metal mounting ring holes are too close together. The mounting holes for the socket should be 28mm ish apart, centre to centre. Would anyone know where i can purchase these that are the correct size? The original one was a brown flat layered socket with the name CINCH stamped on it. It is totally flat and does not "recess" into the chassis hole. There seems to be many B7G sockets available but only with 22 mm mounting holes.
Many thanks as always,
Dave.
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Old 22nd Mar 2014, 6:21 pm   #19
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Default Re: Roberts RMB finally finished but poor intermittent aerial connection.

Hi Dave some pictures would be helpful ! Mick.
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Old 22nd Mar 2014, 6:46 pm   #20
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Default Re: Roberts RMB finally finished but poor intermittent aerial connection.

Dave,

I've got at least a couple of good used non screening can type valveholders that measure 28mm. You're welcome to call and collect them and did I read you need some valves tested. I'll do those for you too.

PM me if I can help.

Jim
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