Octal No 1 pin soldered to shield base rivet
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Location: NSW
Member since 10 June 2010
Member #: 681
Postcount: 1307
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The original hollow rivets I think depend on the rivet being crushed a little when set to provide positive contact between the chassis and the shield base.
I wasn't sure that a washer over the paxolin would allow that with a pop rivet. I have already put in 3mm brass screws and nuts and got good results so will leave any further changes to these fixings until the oscillation problem is fixed. Will start a new thread soon, but the site has been too flaky to try a big post.
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Administrator
Location: Naremburn, NSW
Member since 15 November 2005
Member #: 1
Postcount: 7451
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There is an issue with the site today and I am not sure what is causing it. Write comments to Notepad then copy/paste until things settle. That way there is a backup.
To add to the woes, one of my switches played up at the weekend and needed a right kicking to return to service.
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A valve a day keeps the transistor away...
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Location: Hill Top, NSW
Member since 18 September 2015
Member #: 1801
Postcount: 2116
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There is an issue with the site today and I am not sure what is causing it.
Yeah, not able to connect yesterday, nor today until now. Thanks for keeping it going even though it's a bit sick.
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Location: NSW
Member since 10 June 2010
Member #: 681
Postcount: 1307
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Location: NSW
Member since 10 June 2010
Member #: 681
Postcount: 1307
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I wouldn't mind pop rivets since they would be hidden below the shields, and would provide a vital service - poor shielding can be a killer.
Have steered clear of them because I wasn't sure the paxolin valve bases would take the pressure in the rivet hole, but Ian's experience with a back-up washer is encouraging.
Have used neutral cure silicon to repair speaker cones, and would use anything to ensure safety if there was no alternative. But generally take care with originality, or at least make sure that changes are reversible.
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Location: Wangaratta, VIC
Member since 21 February 2009
Member #: 438
Postcount: 5472
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Pop rivets aka blind aircraft rivets were a product of the 2nd World War. Shrink tubing replaces the rubber that fails on TC fly leads and is good for stopping cloth lead from fraying (ass is circuit board lacquer.
Textile fishing line makes a good sub for tying & binding cable.
Bluetac on the end of a chopstick is good.
Microphonics suggests bad jointing. Rarely the tube. A Viton "O" ring can dampen microphonics in a tube. Lead dress is important wires running parallel and parts away from the chassis all help induction & radiation, which can also manifest as oscillation. Probing with the chopstick and finding a change in oscillation frequency, is a big clue to the problem area.
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Location: NSW
Member since 10 June 2010
Member #: 681
Postcount: 1307
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I have a reel of old fly fishing line which is fabric and as you say is good for tying off. Also can be pressed into service as dial cord, but can need an extra turn around the tuning knob shaft to improve the grip eg AWA 429MA.
The 6A8 is only microphonic while oscillating, as is the rest of the radio. But seems to be centred on the 6A8.
When oscillating just about any wire touched anywhere will change the tone of the whistle. But just poking a plastic knitting needle into the gaps between the wiring at the 6A8 valve base changes the tone so problem appears to show itself worse there. The tube has been checked by swapping out - still oscillation so not to blame.
Joints haven't yet been remade because of the magnitude of the task and inaccesibility. But will attempt soon.
Leads go everywhere on this radio and I have eliminated some associated with the voltage divider, but have otherwise left them untouched except for some safety related renewals especially where problems have occurred (shorts in dial light wires), or deteriorated HT wiring. But as you say still worth a look.
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