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 Post subject: 7058 tube
PostPosted: Jun Wed 12, 2019 12:02 am 
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Joined: May Mon 14, 2018 6:14 pm
Posts: 212
I was at my favorite antique dealer today, and I found some GE NOS 7058 tubes for $1.50 each. The RCA data sheet says pin 9 is not center tapped. So it would seem I cannot use these on parallel heaters. Is there a way to test to see if pin 9 is actually center tapped? There is continuity between 4, 5, and 9.


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 Post subject: Re: 7058 tube
PostPosted: Jun Wed 12, 2019 1:26 am 
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Joined: Aug Sun 23, 2015 6:01 pm
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Location: South Jersey East of Philly
Measure ohms from 4-5 pins....Then measure from pins 9 to 4, and 9 to 5. Each should be half the ohmage of pins 4-5, if center tapped.


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 Post subject: Re: 7058 tube
PostPosted: Jun Wed 12, 2019 2:07 am 
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Joined: May Mon 14, 2018 6:14 pm
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Thank you!


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 Post subject: Re: 7058 tube
PostPosted: Jun Wed 12, 2019 3:09 am 
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Joined: Sep Tue 15, 2015 1:16 am
Posts: 639
Location: 18424 PA
Apparently, not all 7058 have the center tap.


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 Post subject: Re: 7058 tube
PostPosted: Jun Wed 12, 2019 12:52 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Fernandina Beach, FL
n3uvt wrote:
Apparently, not all 7058 have the center tap.

I looked them up and saw the same results! Only one did show the center tap in the brief research that I did.

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Don


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 Post subject: Re: 7058 tube
PostPosted: Jun Thu 13, 2019 3:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Orlando, FL, USA
7058 tubes are not supposed to have the center tap. A 7058 is, essentially , an un-center-tapped 12AX7.


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 Post subject: Re: 7058 tube
PostPosted: Jun Thu 13, 2019 5:03 pm 
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DCW wrote:
I was at my favorite antique dealer today, and I found some GE NOS 7058 tubes for $1.50 each. The RCA data sheet says pin 9 is not center tapped. So it would seem I cannot use these on parallel heaters. Is there a way to test to see if pin 9 is actually center tapped? There is continuity between 4, 5, and 9.

As long as pin 9 has only continuity to 4 & 5, heater is no doubt tapped. Specs note pin 9 as having IC(internal connection). In this application, IC apparently means CT. Likely cheaperr to produce the with CT as there has to be a connection between both sections for series operation. Much info can be gained just by looking inside tube where the leads connect.

Probably best verification would be to connect 6v from pin 9 to 5, does one side light up? Do same with 9 & 4, does opposite side light?

I have a GE 12AV7 that has tapped heater(no surprise) but it also has shield between sections that's in 6BK7 normally connected to pin 9. Shield is not connected. Again probably cheaper(more efficient) to produce tube with shield than without. OR maybe GE needed to fill a large order and was already setup for 6BK7, shift heater connections and start production line.

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Tom


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