Tube Identification Guide

[xlr8or]

I would like to start a thread that focuses on identifying the factory and manufacturing date codes of tubes. I realise that a lot of us come across etched, stamped and printed codes on tubes that are both very easy and very challenging to decipher. I will start with the latter and focus on identifying tubes that were made in the former western block countries in Europe from 1948 to 1955.

 

For this example, I will focus on I what I believe is the best sounding mini triode to be ever manufactured, the ECC40. Two caveats here if you intend to use this tube.

 

1. It can only be used with a 6.3 volt heater. There is no provision for a 12 .6 volt heater on the pin layout for this tube.
2. You will need a rimlock B8A to B9A tube adapter to use this tube in a 9-pin 12AU7/ECC82 socket

 

Now onto the identification guide for codes etched between the pins on the base (see Examples 1 and 3 below) or stamped into the side in a metal collar placed around the base (see Example 2 below).

 

For this exercise will need to reference 3 important tables (all 3 sourced from Brent Jessee's audiotubes website):

 

1. The first table (Table 1) shows the year of manufacture
2. The second table (Table 2) shows the month of manufacture
3. The third table (Table 3) shows the factory codes

 

Table 1: Year of manufacture deciphered codes

 

Table 2: Month of manufacture deciphered codes

 

Table 3: Factory deciphered codes 

So let us now look at Example 1:

 

 

From this photo, the codes on this tube are LCC (first line) and + Z (second line). For the first line, the 'LC' confirms the version and revision of the tube being an ECC40 and the 'C' at the end is the year code. From Table 1 above, the 'C' is linked to 1951 to 1953 production. For the second line, the factory code is '+', which from Table 3 is Sittard, Holland production. The 'Z' from Table 2 aligns to August 1952 production.

 

Moving onto Example 2:

 

 

From this photo, the codes on this tube are DC (first line) and LCC (second line). For the first line, the 'D' represents Hamburg production (Table 3) and the 'C' is the month of manufacture. From Table 2, 'C' aligns to March 1948, 1951 or 1954 production. Let's hold onto that information for the moment. For the second line, the 'LC' again represents the version and revision of the tube being an ECC40 and the 'C' at the end is the year code. From Table 1 above, the C is linked to 1951 to 1953 production. Now if we go back to the first line, the 'C' from Table 2 aligns to March 1951 production. One additional feature that stands out here is that the base of this ECC40 tube has a metal collar, which further confirms much earlier production than Example 1.

 

Let's look at one further example (Example 3):

 

 

From this photo, the codes on this tube are LC2 (first line) and 53 (second line). For the first line, the 'LC' again represents the version and revision of the tube being an ECC40 and from Table 1, '2' aligns to 1948 to 1950 production. For the second line, the '5' represents Toshiba, Japan production (Table 3) and the '3' at the end is the month code. From Table 2 above, the '3' is linked to May 1950 production. Now what is interesting to note in this particular example is that there is no metal collar around the base for 1950 production, which is what would be typically expected based on Example 2. The LC2 code when compared to the LCC code in Example 2 shows the use of a number rather than a letter for the third digit, which still represents the year of manufacture. Numbers always pre-dated letters in tube coding in accordance to Table 1 data. While Valvo were still using the metal collar, Toshiba had moved onto the collarless version of the tube. Philips having multiple tube manufacturing factories located across the world ventured into positioning these factories to compete against each other in terms of their manufacturing technologies to service the world. This is part of the reason why all these tubes are so desirable to own and use in our tube amps and sources.

 

I will stop here for this post. Feel free to share any photos of etched, stamped or printed codes you come across and I'll try my best to help decipher them for you. 

 

Edit: Larger tube porn photos included.

 

Second Edit: I lied. Here are some more codes to decipher. Any guesses? 

 

Edited September 12, 2021 by xlr8or

[LogicprObe]

 

Don't tell me.................this is the simplest tube to decipher!?

 

Keep up the good work.

[Guest crankit]

I have 2 Tungsol 6SN7's that need a birthday 

They maybe late 50's early 60's idk

 

[xlr8or]

The DZ3 and HT3 codes used on the Tung-Sol tubes you have there are extremely challenging to decipher as they represent the actual warranty period, which was typically 12 months after the date of manufacture. However, I have worked out that 'D' is often representative of 1955/1956 production and 'H' is representative of 1959/1960 production. The T and Z represent the quarter but it appears to be offset by 1 month. Therefore, T would be August to October production and Z would be November to January production.

Edited September 17, 2021 by xlr8or

[Guest crankit]

11 hours ago, xlr8or said:

The DZ3 and HT3 codes used on the Tung-Sol tubes you have there are extremely challenging to decipher as they represent the actual warranty period, which was typically 12 months after the date of manufacture. However, I have worked out that 'D' is often representative of 1955/1956 production and 'H' is representative of 1959/1960 production. The T and Z represent the quarter but it appears to be offset by 1 month. Therefore, T would be August to October production and Z would be November to January production.

 

Thank you for the effort and time you put in

 

[Pops110]

Any ideas on these ones @xlr8or. I’ve had the RT 6189’s in the past but they had long plates.

 

 

[xlr8or]

Yes - these RT's are very good sounding tubes. I think they may even be from 1958 with their unique square getter design and copper grid posts. @Aperalim may be able to share further details as he likes an earlier version of the same RT tube.

Edited September 22, 2021 by xlr8or

[Pops110]

 

14 minutes ago, xlr8or said:

Yes - these RT's are very good sounding tubes. I think they may even be from 1958 with their unique square getter design and copper grid posts. @Aperalim may be able to share further details as he likes an earlier version of the same RT tube.

I haven’t seen too many of the square getters for sale.  Had a brief listen this arvo and thought they sounded pretty good.

[Silver Audiophile]

https://www.ebay.com/itm/382547128233?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5337478673&toolid=10001&customid=b958f5cc-1df2-11ec-b7aa-333136613337

 

How could the above be made in Blackburn UK (as per tube's etched code), and be labeled 'made in Holland'?

 

 

[xlr8or]

2 hours ago, Silver Audiophile said:

https://www.ebay.com/itm/382547128233?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5337478673&toolid=10001&customid=b958f5cc-1df2-11ec-b7aa-333136613337

 

How could the above be made in Blackburn UK (as per tube's etched code), and be labeled 'made in Holland'?

 

 

 

They often relabelled tubes this way to sell them as their own under contract. The other thing to keep in mind is that Philips and Mullard were 2 of the same.

 

It's best to ignore any labelling present on the tubes and focus on the factory etched or printed manufacturing date codes to identify their origin. I see so many people refer to say bugle boys. I've seen these tubes interchangeably made in 4 different countries. Again, each tube is very different in tonal character because of the unique internal construction methods and different materials deployed by each manufacturer.

Edited September 25, 2021 by xlr8or