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tomchaoda 7th April 2005 08:12 PM

(RCA) 6SN7 GTC spec?
I recently purchased a RCA 6SN7 GTC metal envelope tube. I am familiar with 6SN7 GT, GTA or GTB; however, I am not able to find any spec regarding GTC? Does anyone know the differece of GTC compare to GTA or GTB?

This photo is here.


Colt45 7th April 2005 09:58 PM

can't say i've heard of GTC. Looks like a relatively recent run though, judging by the box.

Looks like a jan box.. so there should be an acceptance date (sometimes just says "A" and then a date.. )

could be a 1980's revision or something, that has little more difference than the name or something.. i dont know.

Dr. Photon 7th April 2005 10:07 PM

Are you sure that it is a metal tube? why would a metal tube have the GTC (Glass Tubular, revision C) designation. Also, the base looks different (shorter, with a ring around the bottom where the metal envelope clamps on) on the metal tubes I have seen. The base lookslike that a glass tube would have. Are you sure it is a metal tube and not just a glass tube with internal frosting?

Tom Bavis 7th April 2005 11:28 PM

I recall seeing a "metal" 6SQ7 that contained a 6AV6 glass tube inside - made in Brazil if I recall correctly - maybe this is similar?

anatech 7th April 2005 11:47 PM

That really looks like a glass tube. I have to agree with Dr. Photon here.


tomchaoda 8th April 2005 04:08 AM


Are you sure that it is a metal tube?
Yes, I know GT represent "Glass Tube"; however, they really are metal tube. I have receive them and they are made in Brazil. It is very musical and with good bass on my SE amp...

I have a more detailed looks here:


ReinoutdV 8th April 2005 05:28 PM

metal 6sn7
2 Attachment(s)
Hi all,

Tomchaoda is right. These RCA 6SN7M do really exist and as there name already indicates....the M stands for "metal".

Last year i bought a quad at Ebay. Nobody new what they were....the name did not ring any bells. So i bought them quite cheap. The postage from the USA to the Netherlands were higher !

The metal container is quite lightweight, but not uncommon with tubes. The complete metal body made it possible to discard the glass inard container. So the total tube is actually light. And there is NO glass inside.

Soundwise they're nice tubes. Not as good as Tung-Sol VT-231 roundplates (love the bass), or the Sylvania 6SN7W as pictured beside the RCA 6SN7M but on the same level as early RCA's or Ken-Rad's.
They are really better then young Sylvanias (aarrghhh..coinbase) or glass RCA's from the same date.

So yes: i like this Brazilian variety.

I do have to agree with Colt45 on the date: all my 4 tubes have a "D75" imprint. 1975 ?


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