The Reference 6SN7 Thread

[g0ldl10n]

I just received an RCA VT231 / 6SN7GT Grey / Smoked Glass tube and I would appreciate any information you can provide about this tube. It is labeled RCA Radiotron, Made in the USA with a Y5 code. Do you know when the RCA Radiotron logo was used on the 6SN7GT tube and what the date of manufacture is based on the Y5 code?. Looking online (fairly exhaustively), I can’t find any examples of this exact tube with the RCA Radiotron logo.
I can confirm the following, which are characteristic of the RCA VT231 / RCA 6SN7GT version #1 tube:

Base: black with silver labels
Glass: grey extending right from base to near the top, usually opaque
Top mica: round
Other significant features: 2 stabilising rectangular mica ‘ears’ on either side of round top mica. Mica ears often ‘scratch’ out trails in the grey glass.
Not labeled ‘VT-231’ but having ‘RCA’ in a circular logo (with a lightning bolt) labeled in silver print on the base.

Note - I would post pictures, but I can't figure out how to do so. I tried posting the pictures to Pinterest, then using the links here, but it doesn't seem to work for me.
The pictures are at the following Pinterest page:
https://pin.it/2fuV3VG

Thank you!

You can also just right click the picture selecting "copy" then right click in the text field here and click "paste".

 

[Paladin79]

These are the RCA codes I found online

Z - 1936
U - 1937
T - 1938
X - 1939
R - 1940
Y - 1941
S - 1942
K - 1943
H - 1944
V - 1945
F - 1946

1 - JAN-FEB
2 - MAR-APR
3 - MAY-JUN
4 - JUL-AUG
5 - SEP-OCT
6 - NOV-DEC

E stands for OEM

Very good info!

 

[mordy]

You can also just right click the picture selecting "copy" then right click in the text field here and click "paste".

This used to work for me but not any more - now I have to download the picture and then attach it. Don't know why the change.

 

[Paladin79]

“that’s for us to know and for you to find out” …. ==> clandestine mass acquisition of best tubes …

I did load up on specific Melz after that and even gave some away but that was never a secret. I also repaired the pin solder and answered PM’s about which versions to buy.

I also kept a few tubes because I had not seen that many of a specific type. I want to say a GE VT-231 was one of them.

Todays listen will include an all GEC setup with L63’s followed by a dozen tubes I have not heard in a while.

 

[leftside]

I did load up on specific Melz after that and even gave some away but that was never a secret. I also repaired the pin solder and answered PM’s about which versions to buy.

I also kept a few tubes because I had not seen that many of a specific type. I want to say a GE VT-231 was one of them.

Todays listen will include an all GEC setup with L63’s followed by a dozen tubes I have not heard in a while.

There are lot's of different GEC L63 All the way from the 1940's to late 1960's.

 

[Paladin79]

There are lot's of different GEC L63 All the way from the 1940's to late 1960's.

I am not sure of the age on mine, I do like them as well as other single triode tubes I own.
The GEC’s I am listening to are from 1968 since there is a Z on them. I have others in boxes in my shop that should be older, I looked up the codes.

 

[sam6550a]

Nice to know I helped somebody here.

You are the perfect Texas gentleman.

 

[sam6550a]

No surprise...this seller, greengirl613, has been listing poor condition tubes at premium prices.

The premium price is due to the absence of mushrooms.

 

[jonathan c]

Tubes sold by greengirl613 glow from bacterial phosphorescence, not from heated elements …

 

[LoryWiv]

I am not sure of the age on mine, I do like them as well as other single triode tubes I own.
The GEC’s I am listening to are from 1968 since there is a Z on them. I have others in boxes in my shop that should be older, I looked up the codes.

Correct me if I am wrong but I thought the "Z" signified Hammersmith factory. BTW nice to see you sharing the 6SN7 knowledge and your experienced perspective here @Paladin79. I still have the MELZ 1578 pair for which you graciously resoldered the pins for me. Never a whisper of noise after that. You are a great resource (and a gentlemen if I may add w/o embarrassing you too much)!

 

[bcowen]

I did load up on specific Melz after that and even gave some away but that was never a secret. I also repaired the pin solder and answered PM’s about which versions to buy.

I also kept a few tubes because I had not seen that many of a specific type. I want to say a GE VT-231 was one of them.

Todays listen will include an all GEC setup with L63’s followed by a dozen tubes I have not heard in a while.

If it's marked as a VT-231 that would indicate early 1940's production (wartime) and a good likelihood that Ken-Rad actually made it. Whew.

 

[Paladin79]

Correct me if I am wrong but I thought the "Z" signified Hammersmith factory. BTW nice to see you sharing the 6SN7 knowledge and your experienced perspective here @Paladin79. I still have the MELZ 1578 pair for which you graciously resoldered the pins for me. Never a whisper of noise after that. You are a great resource (and a gentlemen if I may add w/o embarrassing you too much)!

You could be right, I found someone who listed the years 1945 to 1968 by letters of the alphabet z being 1968. I am not 100% certain that info is correct.

And you are most kind, I am glad the tubes are working out for you.

 

[Paladin79]

If it's marked as a VT-231 that would indicate early 1940's production (wartime) and a good likelihood that Ken-Rad actually made it. Whew.

Very possible, I am having trouble locating the tube but I believe it was grey glass like this one. I have a box of various VT-231’s packed away somewhere but other projects are in the way.

 

[jonathan c]

You are the perfect Texas gentleman.

… there’s only one there …

 

[greenfielda2]

The Melz from the 70’s and 80’s are certainly not my favorites even though I own some to complete my collection.
The so called 1578’s from the 50’s and early 60’s are another matter entirely. They rated toward the top of over 1500 6SN7’s and equivalents friends and I ran blind tests on. A Sylvania or two did crack the top 25.

My Melzs are marked: II-80, OTK-48, 9. Should be the 80's, right? Nothing available for the 50's Melz, very few available (reliable source) for the 80's these days.