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  #1  
Old 05-24-2018, 09:11 PM
Tom9589 Tom9589 is offline
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Loctal Tubes

Did any other US manufacturer(s) other than Philco use loctal tubes in their B&W television sets?
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Old 05-24-2018, 10:14 PM
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Yeah, although almost none did to the same extent. Early Silvertone TVs actually outdo Philco for engineering of circuits to utilize specific loktal tubes rather than merely swapping sockets to use the types that were nothing more than octals on loktal bases (e.g. 7C5=6V6). The earliest postwar GE and Crosley sets used at least one apiece. Sylvania was augmenting 5U4 with 7X6 in its early 1950s sets;
Motorola also continued to used loktals very occasionally on certain runs of certain chassis into the early 1950s.
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Old 05-25-2018, 09:48 AM
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Some models of the Viewtones used Loctals, and I have a Transvision kit with a few loctals sockets to sub for octal equivalents.

The 7F8 was briefly in vouge in tuners, but they're drift prone. The 6J6 was a better choice.

Last edited by benman94; 05-26-2018 at 01:00 PM.
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Old 05-26-2018, 10:23 AM
dieseljeep dieseljeep is online now
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Quote:
Originally Posted by David Roper View Post
Yeah, although almost none did to the same extent. Early Silvertone TVs actually outdo Philco for engineering of circuits to utilize specific loktal tubes rather than merely swapping sockets to use the types that were nothing more than octals on loktal bases (e.g. 7C5=6V6). The earliest postwar GE and Crosley sets used at least one apiece. Sylvania was augmenting 5U4 with 7X6 in its early 1950s sets;
Motorola also continued to used loktals very occasionally on certain runs of certain chassis into the early 1950s.
The Sears set was a source #101, Colonial Radio, which became Sylvania right around that time.
There seemed to be a tube war for a while!
RCA never used loctal tubes! Philco never used metal tubes or tuning eye tubes, Zenith didn't use metal tubes except in a few post-war models.
Zenith seemed to use Sylvania as one of their prime suppliers.
If there was any metal tubes in a pre-war Zenith, they were repairer installed.
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Old 05-26-2018, 12:15 PM
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Were the loctals in Sears sets branded "Silvertone" ? I don't think that I have seen loctals branded anything but "Philco" or "Sylvania".

jr
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Old 05-26-2018, 01:47 PM
old_coot88 old_coot88 is offline
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Loctals seemed very sturdy and robust electrically back in the day. In 30+ years in the trade, I don't recall ever replacing one.

But in the decades following, some loctals reportedly develop pin-to-socket intermittency from corrosion. Small pin diameter seems to exacerbate it.
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Old 05-26-2018, 03:04 PM
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There was a tremendous advantage to the Loctals that I don't think any manufacturer really explored: compared to an equivalent octal, the parasitic capacitance between the various electrodes was much smaller. I think the reason for this is obvious however; much smaller 7 and 9 pin miniatures came along that were even better in this regard. Still, in the handful of sets that used an octal triode for the local oscillator, the equivalent loctal tube would have likely been more stable at higher frequencies.
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Old 05-26-2018, 03:06 PM
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Quote:
Originally Posted by jr_tech View Post
Were the loctals in Sears sets branded "Silvertone" ? I don't think that I have seen loctals branded anything but "Philco" or "Sylvania".

jr
I've seen GE, CBS, RCA, and of course Sylvania and Philco. Never a Silvertone though...
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Old 05-26-2018, 06:05 PM
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Originally Posted by benman94 View Post
There was a tremendous advantage to the Loctals that I don't think any manufacturer really explored: compared to an equivalent octal, the parasitic capacitance between the various electrodes was much smaller. I think the reason for this is obvious however; much smaller 7 and 9 pin miniatures came along that were even better in this regard. Still, in the handful of sets that used an octal triode for the local oscillator, the equivalent loctal tube would have likely been more stable at higher frequencies.
Digging through my box of loctals, I found a stubby double triode (7F8) which has the triodes lying down, nestled between the pins connected with very short wires to the tube elements. I'm quessing that this was done to minimize capacitance. Odd coincidence, the tube is branded "Silvertone".

jr
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Old 05-26-2018, 06:11 PM
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Yes, the 7F8 was purposely built like that, with mixer and oscillator service in mind. Somewhere I have a paper describing the development of the tube and motivation behind it. GE used it in the 801, 802, 901, and probably the 803 as well. Philco used it in the 1948 model sets. There were a few others as well. It was a good idea, but I've had to buy a bunch of them and hand pick them for least drift.
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Old 05-26-2018, 06:22 PM
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I have a bunch of loktal tubes branded Silvertone.
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Old 05-26-2018, 08:59 PM
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I once had a Silvertone console radio from the post-war period that I believe may have been 100% loctal-probably another Colonial built set as a lot of Sears stuff was in that era.
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Old 05-26-2018, 09:27 PM
dieseljeep dieseljeep is online now
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I once had a Silvertone console radio from the post-war period that I believe may have been 100% loctal-probably another Colonial built set as a lot of Sears stuff was in that era.
Most of their consoles and larger deluxe table models were Colonial built.
Stewart Warner was another big supplier. Arvin built the smaller AA5 type sets.
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Old 05-27-2018, 07:26 AM
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Most of their consoles and larger deluxe table models were Colonial built.
Stewart Warner was another big supplier. Arvin built the smaller AA5 type sets.
Funny you mention Stewart Warner, as I have a 10 or 12 incher from the late 40s with a bunch of loctals in it.

Maybe someone can answer this question for me: Is it 'Loctal' or 'Loktal'? I've seen both, and both have been used in this thread, but I'm not sure what the preferred spelling was per Sylvania...
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Old 05-27-2018, 08:01 AM
Tom9589 Tom9589 is offline
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I’ve always spelled it local. Loktal sounds like a Germanic spelling perhaps.
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