[ARC5] A little off-topic: Metal tubes (eg 6SJ7) seem quite valuable ...

Thu Sep 16 03:02:48 EDT 2021

Thank you very much, Dave!

-- Cheers,
Tom

-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 9/15/2021 20:44, David Rossetti wrote:
>
> Here is an excerpt from the great book "Tube Lore", written by Ludwell 
> Sibley, on the history of metal tubes. Turns out some (most) are all 
> metal (except for the eyelet seals) but there were metal/glass tubes 
> as well.
>
> *THE METAL TUBE*
>
> RCA and GE announced a new technology in April 1934:
>
> the metal tube. Developed in secrecy by GE, the new design
>
> used a steel shell, with individual glass-filled eyelets for the leadin
>
> wires, on a new and convenient octal base. This product line
>
> gave GE and other receiver makers a complete tube complement
>
> for the "1935" line of sets. The "original nine" were:
>
> 5Z4 rectifier
>
> 6F6 power pentode
>
> 6A8 and 6L7 converters
>
> 6H6 duodiode
>
> 6C5 and 6F5 triodes
>
> 6J7 and 6K7 pentodes
>
> A tenth type, the 6D5 power triode, was withdrawn before
>
> major production.
>
> The other tube makers were unhappy to have their product
>
> lines and tooling obsoleted. Some, like Raytheon, signed up to
>
> adopt the new line. Others disparaged RCA's invention - the
>
> multiple eyelet seals were sure to leak, they said - and hurried to
>
> repackage their existing big-pin products with octal bases. Yet
>
> others like Arcturus and Triad quickly devised what they termed
>
> the "perfected" metal tube: the metal-glass (MG) design, where
>
> a small conventional stem-sealed glass tube was hidden inside a
>
> steel shell, on the same octal wafer base as GE-RCA used.
>
> The MG push was short-lived. The RMA issued registration
>
> in July, 1935 on the 5Z4MG, 6A8MG, 6C5MG, 6D5MG,
>
> 6FSMG, 6F6MG, 6H6MG, 6J7MG, 6K7MG - copies of RCA's
>
> line - plus the 25Z5MG rectifier for AC-DC sets. Later registrations
>
> through March 1936 covered the 6N6MG, 6N7MG,
>
> 6Q7MG, and (today unknown) 6Z6MG rectifier. For those
>
> wanting to "collect the set" today, eventual adders were the
>
> 6J5MG, 6XSMG, 25A6MG, and 25Z6MG.
>
> A better variant on the MG idea was the Arcturus "Coronet"
>
> type, which used a new glass "button" stem construction, with
>
> the lead-in wires sealed in a circle. These were used in a line of
>
> octal-based replacement types, to be used with an adapter to
>
> "modernize" existing radios. The line was: 24, 27, 51, 56, 57,
>
> 58, 75, 77, 78, 80, 85, 2A6, and 25Z5. Inherently octal items
>
> (no adapter needed) were: 5Y3 and 25A6 (also replacing 43
>
> with an adapter). Later octal additions were versions of the
>
> RCA "original nine," 6L6 (!), 6N6, 6N7, 6Q7, 6R7, 6X5, and
>
> 25Z6.
>
> Meanwhile RCA overcame great start-up difficulties and got
>
> true metal tubes into full production, introducing additional
>
> types as well. To overcome the high cost of the eyelet base, a
>
> button stem was put into use in 1936. In this design, the glass
>
> stem disc with its lead-in wires was sealed into the bottom of
>
> the metal envelope. The button-stem idea had great benefits in
>
> later tube designs, as we will see. Metal tubes continued to be
>
> registered up to the start of WW II, and even a few variant
>
> types afterward, but other designs took over.
>
> Copies of the original Tube Lore book are hard to come by (they have 
> been out of production for some time) but Sibley released the updated 
> “Tube Lore II” in 2019. You can find it available for purchase from a 
> slew of online book vendors, including Amazon. Great reference.
>
> Dave Rossetti
>
> 410-279-0226 (mobile)
>
> -----Original Message-----
> From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> On 
> Behalf Of Tom Lee
> Sent: Wednesday, September 15, 2021 7:27 PM
> To: arc5 at mailman.qth.net
> Subject: Re: [ARC5] A little off-topic: Metal tubes (eg 6SJ7) seem 
> quite valuable ...
>
> I would guess that there are no metal-over-glass vacuum tubes (the 0Z4 
> and other gas-regulator tubes are not, technically speaking, vacuum 
> tubes, so I'm excluding them). I would be happy to learn of exceptions 
> (as well as the engineering reasons for the exceptions, if possible), 
> but from my limited knowledge, it's hard to see a practical reason to 
> build a glass vacuum tube, and then bond metal to the glass. Shielding 
> is far more cheaply provided in other ways, for example.
>
> -- Cheers,
>
> Tom
>
> --
>
> Prof. Thomas H. Lee
>
> Allen Ctr., Rm. 205
>
> 350 Jane Stanford Way
>
> Stanford University
>
> Stanford, CA 94305-4070
>
> http://www-smirc.stanford.edu <http://www-smirc.stanford.edu>
>
> On 9/15/2021 15:37, William Cromwell wrote:
>
> > Hi,
>
> >
>
> > Looking at the replies regarding glass tubes in metal sleeves it seems
>
> > that some are and others are not. Maybe most are not. I doubt anybody
>
> > here has any reason to report other than their experiences opening
>
> > metal tubes. I may have read some "fake news" once upon a time:)
>
> >
>
> > I was never interested enough to do a post-mortem on dead metal tubes.
>
> > Tubes that work should not be 'molested'. I did harvest a few octal
>
> > plugs from dead glass tubes. Low hanging fruit you know.
>
> >
>
> > 73,
>
> >
>
> > Bill KU8H
>
> >
>
> > bark less - wag more
>
> >
>
> > On 9/15/21 4:48 PM, Ben Hall wrote:
>
> >> On 9/15/2021 3:24 PM, Tom Lee wrote:
>
> >>> My experience is the same as yours. I’ve opened several over the
>
> >>> years, and I’ve never seen one that was simply a metal covering over
>
> >>> an otherwise glass tube.
>
> >> Greetings all,
>
> >>
>
> >> Years ago I obtained a large quantity of assorted tubes - all just
>
> >> thrown into cardboard boxes - all of questionable provenance. After
>
> >> sorting them out, I had about 30 metal octals that were rusty and
>
> >> unidentifiable.  I try not to waste anything, so I cut them all apart
>
> >> to salvage the octal bases. (for what?  I don't know...but I will say
>
> >> I've made a few of them into test adapters, etc...)
>
> >>
>
> >> Every single one had a glass seal between the octal base and the
>
> >> metal envelope, but in all of them, there was no further glass. They
>
> >> were not glass tubes in metal sleeves; once past the glass seal, the
>
> >> metal envelope was what held the vacuum.  :)
>
> >>
>
> >> Thanks much and 73,
>
> >> ben, kd5byb
>
> >>
>
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