The Reference 6SN7 Thread

JTbbb · Jan 6, 2023 at 4:34 PM

Isaacc7 said:
The consensus seems to be that the 6f8g and 6sn7 round plate black glass are the same thing. Tung Sol didn’t make a 6j5 with the same plate. There are round plate 6j5gt tubes labeled Tung Sol but they are actually Sylvania tubes. They are good tubes but don’t sound like the Tung Sol 6sn7.

This is a flat plate is it not?

LobalWarming · Jan 6, 2023 at 4:45 PM

JTbbb said:
This is a flat plate is it not?

It's the ladder. ;--)

Isaacc7 · Jan 6, 2023 at 4:48 PM

JTbbb said:
This is a flat plate is it not?

Yup, and I believe that those are actually made by Tung Sol. Much earlier in this thread there were some pictures of tungsol 6j5gt with round plates but they are identical with Sylvania 6j5gt. Incidentally, those Sylvania tubes are pretty cheap and well worth hearing. Like all tubes, they don’t match with everything but they can match well with some.

hottyson · Jan 6, 2023 at 9:44 PM

Somatic said:
Wondering what is a good tube tester for beginners? I am looking to test 6SN7, 6F8G and 6J5 variants. Thank you.

I do own a Dyna Jet 606 tube tester. However, for a beginner one might already be set testing tubes in their amplifiers. I test my 6SN7 tubes every time I insert them in my Darkvoice tube amplifiers or my Eufonika H5DS tube amplifier using my hearing. This seems useful enough instead of plugging them into Dyna Jet 606. If they sound balanced and matched, all is well. I also sometimes try to purchase more than one of the same tube so that I can compare them A/B in my amplifiers to hear if there might be something comparably wrong with a tube. The Dyna Jet mostly becomes handy at times after I have heard something wrong with a tube.
.
My Dyna Jet 606 is easy to use and beginner friendly. It requires that one look up the tube being tested within the included manual, and then dial in the settings, and finally press the test button. Simple. However, if you are going to purchase a tube tester, you probably should not skimp and should go straight for a well regarded Hickok tester. Hickok testers can be repaired more easily if something goes wrong because they contain replaceable/acquirable parts.

lupoal · Jan 7, 2023 at 6:55 AM

mordy said:
Here is a reference to different EIA code lists for different years:
https://www.ecianow.org/eia-source-codes

As far as I know the EIA codes did not change for manufacturers, but perhaps a code was added when a company would buy another company (?).

Regarding you Sylvania question, a number of companies switched to different date coding systems, or sometimes even having two systems being used at the same time - for example for civilian and military use. Usually the military date code is straight forward - 52-39 would mean 39th week 1952.

Sylvania tubes from the early 50s have two date codes - one on the base of the tube and one on the glass under the tube designation logo. Presumably one code is manufacturing date and the other shipping date - there could be several months discrepancy.
Here is an example - a Motorola 6J5GT tube. The base says 312026 and under the 6J5GT on the glass it says COM.
COM:
C = March (count ABC on your fingers but skip I because it is too easily confused with 1)
0 = 1950
M = maybe the factory

312 is the Sylvania EIA code
026 means 1950 26th week (June)

So the tube was made in March 1950 and shipped in June 1950.

Another example - a FoMoCo 6J5GT tube (Ford Motor Company) has the following codes:
L9M and 312 026.
L = November
9 = 1949
M = factory
312 and 026 as above; in other words both tubes were shipped at the same time but manufactured several months apart.

Tung Sol codes are a complete mystery - it appears that the date codes indicate the end of the warranty period. Sometimes the original tube box will have a date printed, and you may be able to compare it to the date code on the tube base.

Sometimes the date code follows the alphabet but starting in the middle with N being the starting point (January). I have an Arcturus 6N7G tube that says N4 N4 on the base. IMHO it means that the tube was manufactured and shipped in January 1944.

Except for the military dating code there is no real standard and each manufacturer may use their own system.

thanks

in the meantime I've received some additional info from one of my friends, I will share here in case could be interesting/useful...

RMA/EIA Open Date Code

Starting in 1946 the American tube manufactures agreed to an open date code printed on their tubes. It was a 3-digit numerical code with the first number representing the year. It was followed with a two digit number representing the week it was made.
This was to standardize date-codes that were on American made tubes. Until 1946 there were a confusing array of secret code systems known only to the tube company. Each company had their own individual secret code.
6 is 1946
7 is 1947
8 is 1948
9 is 1949
0 is 1950
1 is 1951
2 is 1952
3 is 1953
4 is 1954
5 is 1955
example: the date-code 601 means the tube was manufactured the first week of 1946; another date would be 945 and would mean the forty-fifth week of 1949; and the date of 450 means the fiftieth week of 1954.
In 1955 they started using the 4 digit open code system with the first two numbers representing the year. So..
1. 55 is 1955
2. 56 is 1956
3. 57 is 1957
4. 58 is 1958
5. 59 is 1959
and so on.
example: 55-09 means the ninth week of 1955; 59-43 would be the forty-third week of 1959.
At the same time some companies like RCA also used a secret in-house date-code of two letters like KH on SOME of their tubes. The first letter represented the year and the second letter was the month of manufacture. They used this two letter system mainly in the mid 1950s and then again in the mid 1960s.
At the same time they were also still using the using the open code system. I am not sure why they went back to a secret code for some of their tubes.

so it seams my tubes could be from April 1951... happy about that

mordy · Jan 7, 2023 at 7:33 PM

Isaacc7 said:
The consensus seems to be that the 6f8g and 6sn7 round plate black glass are the same thing. Tung Sol didn’t make a 6j5 with the same plate. There are round plate 6j5gt tubes labeled Tung Sol but they are actually Sylvania tubes. They are good tubes but don’t sound like the Tung Sol 6sn7.

I have Tung Sol 6F8G flat plates - do they sound different than the round plates?

ColSaulTigh · Jan 7, 2023 at 7:37 PM

mordy said:
I have Tung Sol 6F8G flat plates - do they sound different than the round plates?

Slightly, but not enough to get too bent out of shape about. Slightly dryer. That's about it.

triod750 · Jan 7, 2023 at 7:40 PM

What about the difference between 6C8G and 6F8G? What magnitude and in what way?

mordy · Jan 7, 2023 at 7:44 PM

lupoal said:
thanks
in the meantime I've received some additional info from one of my friends, I will share here in case could be interesting/useful...

RMA/EIA Open Date Code

Starting in 1946 the American tube manufactures agreed to an open date code printed on their tubes. It was a 3-digit numerical code with the first number representing the year. It was followed with a two digit number representing the week it was made.
This was to standardize date-codes that were on American made tubes. Until 1946 there were a confusing array of secret code systems known only to the tube company. Each company had their own individual secret code.
6 is 1946
7 is 1947
8 is 1948
9 is 1949
0 is 1950
1 is 1951
2 is 1952
3 is 1953
4 is 1954
5 is 1955
example: the date-code 601 means the tube was manufactured the first week of 1946; another date would be 945 and would mean the forty-fifth week of 1949; and the date of 450 means the fiftieth week of 1954.
In 1955 they started using the 4 digit open code system with the first two numbers representing the year. So..
1. 55 is 1955
2. 56 is 1956
3. 57 is 1957
4. 58 is 1958
5. 59 is 1959
and so on.
example: 55-09 means the ninth week of 1955; 59-43 would be the forty-third week of 1959.
At the same time some companies like RCA also used a secret in-house date-code of two letters like KH on SOME of their tubes. The first letter represented the year and the second letter was the month of manufacture. They used this two letter system mainly in the mid 1950s and then again in the mid 1960s.
At the same time they were also still using the using the open code system. I am not sure why they went back to a secret code for some of their tubes.

so it seams my tubes could be from April 1951... happy about that

You do need one more piece of the puzzle - when did the manufacturers switch from 6SN7GTA to GTB?

Here is a reference to RCA coding. The early stuff is confusing, but the letter codes 1956 to 1976 are easy:
https://moam.info/date-codes-for-rca-made-tubes-ludwell-sibley_59c536a71723dd2a1c99fa60.html

BTW, I have a RCA labeled tube with a two letter code that does not appear in the chart, but can be found in a GE letter chart; however, no white dots...

paradoxper · Jan 7, 2023 at 7:46 PM

Somatic said:
Wondering what is a good tube tester for beginners? I am looking to test 6SN7, 6F8G and 6J5 variants. Thank you.

Grab the Amplitrex AT1000. It is amongst the best and will provide you a peace of mind with 300B.

mordy · Jan 7, 2023 at 7:57 PM

paradoxper said:
Grab the Amplitrex AT1000. It is amongst the best and will provide you a peace of mind with 300B.

I would grab one too, but I believe that the price is in the $3000 range...

ColSaulTigh · Jan 7, 2023 at 8:10 PM

mordy said:
I would grab one too, but I believe that the price is in the $3000 range...

INB4 "buy one, cry once".

mordy · Jan 7, 2023 at 9:09 PM

ColSaulTigh said:
INB4 "buy one, cry once".

WAF (Wife Approval Factor) ?

raindownthunda · Jan 7, 2023 at 9:22 PM

mordy said:
I would grab one too, but I believe that the price is in the $3000 range...

I wish the local library had tube testers.

mordy · Jan 7, 2023 at 9:30 PM

raindownthunda said:
I wish the local library had tube testers.

I remember when Radio Shack and hardware stores had tube testers....

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The Reference 6SN7 Thread

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RMA/EIA Open Date Code​

​

Starting in 1946 the American tube manufactures agreed to an open date code printed on their tubes. It was a 3-digit numerical code with the first number representing the year. It was followed with a two digit number representing the week it was made.​

This was to standardize date-codes that were on American made tubes. Until 1946 there were a confusing array of secret code systems known only to the tube company. Each company had their own individual secret code.​

6 is 1946​

7 is 1947​

8 is 1948​

9 is 1949​

0 is 1950​

1 is 1951​

2 is 1952​

3 is 1953​

4 is 1954​

5 is 1955​

example: the date-code 601 means the tube was manufactured the first week of 1946; another date would be 945 and would mean the forty-fifth week of 1949; and the date of 450 means the fiftieth week of 1954.​

In 1955 they started using the 4 digit open code system with the first two numbers representing the year. So..​

1. 55 is 1955​

2. 56 is 1956​

3. 57 is 1957​

4. 58 is 1958​

5. 59 is 1959​

and so on.​

example: 55-09 means the ninth week of 1955; 59-43 would be the forty-third week of 1959.​

At the same time they were also still using the using the open code system. I am not sure why they went back to a secret code for some of their tubes.​

Headphoneus Supremus

Headphoneus Supremus

Headphoneus Supremus

Headphoneus Supremus

500+ Head-Fier

Headphoneus Supremus

Users who are viewing this thread

RMA/EIA Open Date Code

Starting in 1946 the American tube manufactures agreed to an open date code printed on their tubes. It was a 3-digit numerical code with the first number representing the year. It was followed with a two digit number representing the week it was made.

This was to standardize date-codes that were on American made tubes. Until 1946 there were a confusing array of secret code systems known only to the tube company. Each company had their own individual secret code.

6 is 1946

7 is 1947

8 is 1948

9 is 1949

0 is 1950

1 is 1951

2 is 1952

3 is 1953

4 is 1954

5 is 1955

example: the date-code 601 means the tube was manufactured the first week of 1946; another date would be 945 and would mean the forty-fifth week of 1949; and the date of 450 means the fiftieth week of 1954.

In 1955 they started using the 4 digit open code system with the first two numbers representing the year. So..

1. 55 is 1955

2. 56 is 1956

3. 57 is 1957

4. 58 is 1958

5. 59 is 1959

and so on.

example: 55-09 means the ninth week of 1955; 59-43 would be the forty-third week of 1959.

At the same time they were also still using the using the open code system. I am not sure why they went back to a secret code for some of their tubes.