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Origin of the 6L6GC?

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Posted on July 20, 2013 at 06:51:04
Thermionic27609
Audiophile

Posts: 390
Joined: March 29, 2009
A friend was asking me, in connection with his amp, when the GC version of the 6L6 first became available. I had a rough idea, but didn't know offhand, so I started looking around. I was hoping Asylum members might have more data.

Eric Barbour wrote a 1996 article on the 6L6 for VTV, but he equivocates on the origins of the GC version:

"In 1959, a five-ply combination metal sandwich type plate design and a different maximum rating system allowed the 6L6GC to raise the plate dissipation from 19 to 30 watts."

The sentence is structured such that he avoids directly stating which manufacturer came up with this five-ply plate design.

This 1960 General Electric document that touts their five-ply plate material makes it sound like it's GE's innovation.

http://n4trb.com/AmateurRadio/GE_HamNews/issues/GE%20Ham%20News%20Vol%2015%20No%201.pdf

I found a couple of other references online that suggest that GE developed this plate material, including a post by Ned Carlson who wrote that GE introduced the 6L6GC in 1961. But then, there's a '59 GE 6L6GC datasheet that states in a note that it supercedes an earlier '58 document. Sylvania published a 6L6GC datasheet in 1959. The earliest RCA 6L6GC datasheet I can find is 1960.

Finally, the first Fender amp I can find that lists the 6L6GC on the schematic, rather than 5881s, is the 1959 (according to the Fender Field Guide site) 5G13 "brown" Vibrasonic.

I once saw a tube data book that indicated which company registered any given new tube type, but I don't have access to it anymore.

So, who first stamped "6L6-GC" on a tube and sent it to market?

 

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RE: Origin of the 6L6GC, posted on July 20, 2013 at 08:01:59
unclestu
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IIRC, the five ply plate construction was an explosion welded piece where explosives were used to bond dissimilar materials ( i.e. Aluminum and nickel). Still used to today by navy suppliers to bond aluminum and steel (bimetallic strips and plates, steel side for the main deck and lower hull, aluminum for the upper decks to keep the ships from being excessively top heavy).

IIRC, TI ( yep, Texas Instruments or what eventually became TI) developed the procedure. If so, the material would hardly be proprietary to the major electronics companies.

Incidentally the multiple plate construction was responsible for the GE 6550A's higher output, so there is a strong suspicion on my part that GE was the first tube manufacturer to use that particular construction. IIRC RCA's answer was the 7027.

 

RE: Origin of the 6L6GC, posted on July 20, 2013 at 08:50:43
Thermionic27609
Audiophile

Posts: 390
Joined: March 29, 2009
Thanks for the information on the Texas Instruments connection.

AFAIK, the RCA 7027 appeared in 1958 (Barbour's VTV article and RCA datasheets), while the GE 6550A doesn't arrive on the scene until the late 60s, possibly even early 70s.

 

Actually, posted on July 20, 2013 at 18:05:08
unclestu
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I happened to unpack my old issues of VTV.

6550A's by GE were introduced in 1971. Other tidbits uncovered in rereading the article, The metal ring around the octal base was designed to be at cathode potential for "safety and improved electrical stability".
Tung Sols had low loss bases with "molded in dams between the pins to discourage leakage currents."

Barbour claims the grid wires on Tungsols were gold plated !

 

RE: Actually, posted on July 20, 2013 at 18:08:51
Eli Duttman
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Posts: 10426
Location: Monroe Township, NJ
Joined: March 31, 2000
"Barbour claims the grid wires on Tungsols were gold plated !"

It's commonplace for control grids to be gold plated. Doing so blocks unwanted secondary emission from the helix.


Eli D.

 

Common on RF tubes maybe, posted on July 20, 2013 at 19:55:45
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
not so common for a tube designed for consumer audio

 

Gold plated g1 show up on a lot of audio power tubes..., posted on July 21, 2013 at 05:19:08
Steve O
Audiophile

Posts: 10277
Location: SE MI
Joined: September 6, 2001
...6L6GC, 5881etc. I've even seen them on relatively recent Russian power tubes.

 

RE: Origin of the 6L6GC, posted on July 21, 2013 at 09:47:07
Thermionic27609
Audiophile

Posts: 390
Joined: March 29, 2009
Confirmation on Texas Instruments' development the 5-layer plate material. Patent applied for in 1959, granted 1963.

US Patent: 3112185

 

RE: Actually, posted on July 21, 2013 at 10:03:34
Thermionic27609
Audiophile

Posts: 390
Joined: March 29, 2009
To be more specific, Tung Sol claimed that their control grids were gold-plated as far back as their 1950 description of the design of the 5881.

On their 1954 6550 advertisement, they claim, "Maximum control of grid emission achieved by gold plating and carbonizing."

As a Leslie amp tech, I always check for grid emission when servicing amps, and I find that the old Tung Sols are, in fact, surprisingly immune to grid emission problems, more so even than the GE 6550A.

 

RE: Common on RF tubes maybe, posted on July 22, 2013 at 05:56:28
Jim McShane
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Location: Chicago
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As Steve said, it was indeed quite common on "audio" tubes too. The current Genalex power tube reissues have gold plated control grids, as do some of the 300B - there are a number of others as well.

 

RE: Origin of the 6L6GC?, posted on July 22, 2013 at 12:29:50
Tom Bavis
Audiophile

Posts: 899
Location: Upstate NY
Joined: May 25, 2007
"Tube Lore" lists the registration date for each number, but doesn't indicate what company registered it. 7027 came first (3-58), then 6L6GC (11-58), and 7581 was registered in 1959.

 

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