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 Post subject: Loctal-8 tube question
PostPosted: Sep Tue 28, 2021 12:52 am 
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Joined: Jan Sun 12, 2020 8:43 pm
Posts: 150
Location: Palm Harbor, Fl 34684
My basic query of the week, using as an example, a 7A8 tube, in which stem is not phenolic, yet under chassis there are connections to it. Is it a negative or does the stem play an actual active part in the scheme of things?


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 Post subject: Re: Loctal-8 tube question
PostPosted: Sep Tue 28, 2021 1:55 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 4100
Location: Austin, Texas
The metal base of the Loctal tubes acts as a shield and a connection for an additional shield if needed. The base is usually connected to the radio chassis.

Jay


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 Post subject: Re: Loctal-8 tube question
PostPosted: Sep Tue 28, 2021 10:28 pm 
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Joined: Dec Tue 23, 2014 6:51 pm
Posts: 2414
Location: N. Palm Bch, Fl.
I noticed this on some of the radios I work on. The ones where B- does not go to the chassis, They tie them together and then to the chassis. Only on the RF/IF tubes. The Detector and Output tubes have no wires connected to that tab. So it must be for shielding as Jay said. Some of the 7 pin fiber sockets have those center tabs and you will find them also all tied together and grounded to the chassis. They look like a little rivet yet the tubes are all glass. Seems like a lot of extra work for the assembly line. The engineers are a lot smarter then I for sure, so there must be a good reason.

Freeman


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