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Old 25th Dec 2019, 10:24 am   #12
cathoderay57
Octode
 
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 1,206
Default Re: Marconiphone 538

The screening arrangement inside the KTW63 and 6K7G might well be different. The KTW63 certainly creates a squeal like a stuck pig if I remove the external metal shielding can. The can is supposed to be earthed by contact as it slides over 2 pips on the valveholder metal skirt, then twists and locks. Even though there was good electrical contact between the metal shield can and the base skirt the problem remained. The issue appeared to be that the while the metal skirt is earthed to chassis via the rivets that hold the skirt, the paxolin valveholder and the chassis together, there is probably some corrosion between the rivets and the chassis holes creating an intermittent joint. I suppose I could have drilled out the rivets, cleaned it up and fitted screws but it was simpler just to solder on an earth bonding lead. Anyhow, it's fixed! Happy Christmas to all. Cheers, Jerry
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