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 Post subject: Philco 38-4 tube subsitution
PostPosted: May Mon 17, 2021 1:36 am 
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Joined: Sep Wed 03, 2014 11:06 pm
Posts: 316
Location: Poulsbo, Wa
I just got a philco 38-4 in pretty good shape, It is missing the 6a8g tube.
Can i sub a 6a8gt tube?
Cant wait to play with they tuning cones.

Thanks

Bill


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 Post subject: Re: Philco 38-4 tube subsitution
PostPosted: May Mon 17, 2021 1:52 am 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 8020
Location: Near Brandon, Iowa
The 6A8GT will electrically work the same as the 6A8G tube but thanks to Philco's attempts at corralling the replacement tube market for their brand, it may not physically fit into the socket due to interference with the tube shield base. The 6A8GT is wider diameter at its base than the 6A8G.

You can cut away the tube shield base and use the 6A8GT, but that will compromise the "originality" of the chassis. It's up to you if this is acceptable or not. If you do this, connect pin 1 of the socket to chassis ground- the 6A8GT is internally shielded so no metal shield is needed. Pin 1 serves as the internal shield connection.

The "cone preset" system seems to be clever at first blush but it generally sucks. Philco abandoned it after a couple of model years.


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 Post subject: Re: Philco 38-4 tube subsitution
PostPosted: May Mon 17, 2021 10:46 am 
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Joined: Jun Sun 03, 2012 12:40 am
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Location: Cromwell, Connecticut
Unless I’m missing something, won’t a 6A8GT need a shield? A 6A8 metal tube would not, but pin 1 needs a ground.

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People may not remember how fast you did a job, but they will remember how well you did it.


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 Post subject: Re: Philco 38-4 tube subsitution
PostPosted: May Mon 17, 2021 2:11 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 8020
Location: Near Brandon, Iowa
Tbone wrote:
Unless I’m missing something, won’t a 6A8GT need a shield? A 6A8 metal tube would not, but pin 1 needs a ground.

6A8GT like most GT-series signal tubes has a built-in electrostatic shield, making an external shield unnecessary provided pin 1 of the socket is grounded, as I mentioned earlier.

https://www.radiomuseum.org/tubes/tube_6a8gt.html

The shield is drawn as a heavy black circle around the tube elements that is connected to pin 1 of the tube base.


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 Post subject: Re: Philco 38-4 tube subsitution
PostPosted: May Mon 17, 2021 5:10 pm 
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Joined: Sep Wed 03, 2014 11:06 pm
Posts: 316
Location: Poulsbo, Wa
If there was a tube shield base it is gone now. Just holes for the tube.

I also can move the dial around and have been reading about the three position dial knob , but the gang does not turn as the pointer does.
Stuck somehow. Still looking... update...seems just need a tightening at the screw,

Thanks

Bill

Ps i found a NOS- 6A8MG glass tube enclosed in metal i assume that would be the best of both worlds here?


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