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.

Sylvania was the developer of the Loktal tubes, which were a rebuttal to RCA's metal tubes. They were introduced around 1939, and quickly became adopted by Colonial, Philco and Zenith; the three manufacturers who were unwilling to use the metal tubes, and pay royalties to RCA for using them. All three had close ties to Sylvania as an OEM tube supplier.

RCA wasted no time in firing back with the all-glass miniature tubes, just as WWII was about to start. The Loktal tubes hung around for a few years after the war, but were pretty much obsolete by the early 1950s.

There is one major advantage to the loctal today compared to the octal for audio applications: price!

I don't claim to be able to hear the difference between different tubes of the same type, ie tube rolling, as I'm slowly going deaf in one ear. That said, I do know that my wallet much prefers spending $3 on a 7N7 vs $10 on a 6SN7. In particular, some Sylvania 6SN7s can fetch $100+ for a single NOS example on eBay, whereas literally the same exact tube, with the same exact internal construction, but on a loctal base will net $2 to $5...

I won't use any of the extremely expensive octals in a DIY setting anymore; only the loctal equivalent if it exists. Paying more when you don't have to for equivalent performance is downright insane.