Loctal Tubes
 

Did any other US manufacturer(s) other than Philco use loctal tubes in their B&W television sets?

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.

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.

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.

Were the loctals in Sears sets branded "Silvertone" ? I don't think that I have seen loctals branded anything but "Philco" or "Sylvania".

jr

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.

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.

I've seen GE, CBS, RCA, and of course Sylvania and Philco. Never a Silvertone though... :scratch2:

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

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.

I have a bunch of loktal tubes branded Silvertone.

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.

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...

I’ve always spelled it local. Loktal sounds like a Germanic spelling perhaps.

:D According to the least reliable source of info on the net (Wikki) the name for the tube was "loctal" for "lock in octal" for all who used it except Sylvania , who trademarked the "Loktal" spelling . So if this is true , for Philco it's loctal and for Sylvania it's loktal .

That’s a logical explanation. Thanks.

Another fun fact about the loctal types, though rather useless for TV, is that they have a ruggedized heater-cathode assembly to allow overvoltages of up to 7 volts. This is the approximate voltage from a fully charged 6.3 volt car battery with the alternator running as well.

I have a Williamson I built with 7A4s in the first four stages and Sylvania 807Ws for the output tubes, with a regulated 6.3 volt heater supply. I expect the loctals out front to last until Armageddon...

:) Small correction , but since you didn't grow up with 6 volt cars you are automatically forgiven ;

All cars in the 6 volt era had generators , in fact the generator outlived the 6 volt system and the earliest 12 volt cars still had an actual DC generator . My 53 Buick was the last GM 6 volt car , and the last straight eight engine , in 1954 GM eliminated both the straight eight and the 6 volt system but the generator still hung around in GM cars till at least 1961 because my 61 caddy had a generator (with it's 12 volt system) . My 64 caddy was the first car I owned that had an alternator , which BTW in car use the alternator IS by far the better suited machine , generators with their full current brushes were a far more frequent replacement item than today's alternators are :D

:thmbsp: Oh , and I forgot to mention , yea I've always been a fan of loctal tubes as well , to me it seemed a more robust design having a tube that wouldn't wiggle it's way out of it's socket with vibration present .

And Wikki seems to be incorrect again. :D

https://farm1.staticflickr.com/973/4...a1ec81_z_d.jpg


jr

:D Yep , the absolute least reliable source of info on the net .

"Vetting ???? We don't need no stinkin vetting !!!"

:scratch2: Ever wonder how wikki still exists in a world where facts shouldn't be all that hard to come by ?

There's nothing quite like the silent rage that comes from seeing your wiki edit to correct their misinformation reversed.

GM switched over to alternators in MY 1963. Ford switched over in MY 1965. Chrysler beat them all with alternators in MY 1960. It's not uncommon to have alternators with 150 amp capacities these days. Can imagine what a 150 amp generator would look like?

My brother had a 1963 Valiant with a generator and was still 6 volts

That does not sound correct. Chrysler switched to 12 volts in the mid 50s. I had a '57 Plymouth and it had a generator but was 12 volts. Chrysler went to alternators in all 1961 cars.

It might've been an Australian model!

A slight mistake here. The Aussie makes were like the British makes, 12V even before ours were changed.
The European cars were 6V for several years after.
A note on the GM's. The 54 Pontiac was a flat-head straight 8 and still 6V.
All the 54 Chevs including the first Corvette was 6V. :scratch2:

My '63 Fury had an alternator with 12 volts.

In Australia in the sixties the only 6V vehicles were VW,s. There were some English cars with positive earth however AFAIK.

Something else to make it more confusing. Sylvania was a major supplier of tubes for Philco.

I found a few tubes in my unsorted box that did not have the usual locator bump on the side of the metal base. These were mostly labeled Zenith and GM, with one Admiral tube in the mix.... any idea who made them? :scratch2:

jr

If there is a 3-4 digit EIA code on them anywhere then it should be easy to tell...I've done that on some Silvertone badged CRTs I've had that I was curious about.

I inherited a test transmitter which was owned by my grandfahter since it was new in 1952. Last December I had to replace the original european made ECH21 loctal tube due to the fact that the test tone oscillator didn't work any more. The RF carrier was still there. Not too bad for it's age :scratch2:
In the meantime I already bought a few nos tubes for safty reasons :smoke:
I'm looking forward to do a little introduction of this device sooner or later.

I didn't see any when I pulled them out of the box... perhaps the tubes are too old to have EIA code markings, or they have mostly rubbed off. I went back and double checked and did find a faint code on the Admiral tube.... It appears ro read "713", which is Taylor, a Chicago mfg, mostly known (by me, at least) for their transmitter tubes and mercury vapor rectifiers. Perhaps they did source receiving tubes for Admiral. :scratch2:

jr

One thing common to most of the loctal tubes I've seen is that the ink rubs off VERY easily.

I can only think of one other tube that has "Magic Disappearing Ink". Telefunken Audio tubes! And you know how fussy Audiophools are...:rolleyes:

It seems unusual that the Government suppliers weren't that crazy about them, even though they seemed to be as you say.
They were used, but not in too many applications. :scratch2:

Also the loctal tube has a metal base that should help act like shielding between say the control grid (input) and the plate (output) to avoid an IF stage from oscillating. Assuming the socket's metal snap-in grip is grounded.

It's loktal. Also laurel.