The Reference 6J5 Thread (L63, 6C5, 12J5, 6P5, etc.)

[whirlwind]

Here is my B36 metal base...not very good pics however


This is a d getter.

 

[Tom-s]

Not a 6J5 but a tube worth mentioning. I posted about this one in the Bottlehead Crack thread.

The 6J5 was developed somewhere in 1936. Somewhere in 1937 a pair of 6J5G's was placed in a single envelope and the 6F8G was first registered Sept 24 1937.

This was the first double triode (with separate cathodes) and popular in these places. It's successor, introduced in 1939 as the 6SN7, is even more popular.

The Sylvania shown here is from Oktober (J) 1937 (7) and has an engraved (hot stamped) base (Sylvania went to their yellow silk screen mid 1938).

It must be one of the first 6F8G's ever to be mass produced and has a unique build. It uses the round anode construction seen in some military Sylvania 6J5GT (VT-94D).

My later Sylvania 6F8G and VT-99 (WWII era tubes) all have T plates with grid cooling above the top mica.

This is the only 6F8G in my collection that predates any 6SN7.

Here's a recent post with the single Sylvania 6J5GT's with a similar round anode build.

Here's a topic with explanation for Sylvania date codes.
Oh, and here's how to figure out RCA date codes.

Enough for the history lesson. It sounds great. Haven't compared it yet to other 6F8G's yet. Here's some pictures (while in use).

 

[Slade01]

Not a 6J5 but a tube worth mentioning. I posted about this one in the Bottlehead Crack thread.

The 6J5 was developed somewhere in 1936. Somewhere in 1937 a pair of 6J5G's was placed in a single envelope and the 6F8G was first registered Sept 24 1937.

This was the first double triode (with separate cathodes) and popular in these places. It's successor, introduced in 1939 as the 6SN7, is even more popular.

The Sylvania shown here is from Oktober (J) 1937 (7) and has an engraved (hot stamped) base (Sylvania went to their yellow silk screen mid 1938).

It must be one of the first 6F8G's ever to be mass produced and has a unique build. It uses the round anode construction seen in some military Sylvania 6J5GT (VT-94D).

My later Sylvania 6F8G and VT-99 (WWII era tubes) all have T plates with grid cooling above the top mica.

This is the only 6F8G in my collection that predates any 6SN7.

Here's a recent post with the single Sylvania 6J5GT's with a similar round anode build.

Here's a topic with explanation for Sylvania date codes.
Oh, and here's how to figure out RCA date codes.

Enough for the history lesson. It sounds great. Haven't compared it yet to other 6F8G's yet. Here's some pictures (while in use).

The engraved based and font lettering is insane/cool, i've never seen it until now. Thank you very much for sharing!

 

[Marutks]

Two versions of the B65/36 also exist; brown base clear glass, and metal base grey or clear glass. From what I have found, the plate structures of the brown base tubes correspond directly, but I lack a metal base B65/36 to inspect closely myself and confirm.

I have got metal base GEC B36. The internal structure seems to be identical to brown base Osram B36.

 

[mordy]

Not a 6J5 but a tube worth mentioning. I posted about this one in the Bottlehead Crack thread.

The 6J5 was developed somewhere in 1936. Somewhere in 1937 a pair of 6J5G's was placed in a single envelope and the 6F8G was first registered Sept 24 1937.

This was the first double triode (with separate cathodes) and popular in these places. It's successor, introduced in 1939 as the 6SN7, is even more popular.

The Sylvania shown here is from Oktober (J) 1937 (7) and has an engraved (hot stamped) base (Sylvania went to their yellow silk screen mid 1938).

It must be one of the first 6F8G's ever to be mass produced and has a unique build. It uses the round anode construction seen in some military Sylvania 6J5GT (VT-94D).

My later Sylvania 6F8G and VT-99 (WWII era tubes) all have T plates with grid cooling above the top mica.

This is the only 6F8G in my collection that predates any 6SN7.

Here's a recent post with the single Sylvania 6J5GT's with a similar round anode build.

Here's a topic with explanation for Sylvania date codes.
Oh, and here's how to figure out RCA date codes.

Enough for the history lesson. It sounds great. Haven't compared it yet to other 6F8G's yet. Here's some pictures (while in use).

There is another similar tube with the same pinout that predates the 6F8G with a couple of months - the 6C8G (Jan 21, 1937). It is a double triode but the heater current is 0.3A compared to 0.6A for the 6F8G.
IMHO the sound is similar as I recall, and the prices are much lower - it is not as well known as the 6F8G.

 

[tubebuyer2020]

There is another similar tube with the same pinout that predates the 6F8G with a couple of months - the 6C8G (Jan 21, 1937). It is a double triode but the heater current is 0.3A compared to 0.6A for the 6F8G.
IMHO the sound is similar as I recall, and the prices are much lower - it is not as well known as the 6F8G.

Also, the 6C8G tends to be confused with some sort of a 6SL7 predecessor for some weird reason - despite having a twice smaller amplification factor.

 

[Tom-s]

There is another similar tube with the same pinout that predates the 6F8G with a couple of months - the 6C8G (Jan 21, 1937). It is a double triode but the heater current is 0.3A compared to 0.6A for the 6F8G.
IMHO the sound is similar as I recall, and the prices are much lower - it is not as well known as the 6F8G.

Thanks @mordy; for this.

They don't only sound similar. They were also build very similar. Could have been the same production line on a different day. Most of my 6F8G and 6C8G look alike when from the same manufacturer.

Here's an example from a National Union tube type 6F8G and 6C8G. Both carry the same base (with date code 1U) and very much similar internal construction.
And here's a link to a 6J5 with a similar internal structure: http://www.r-type.org/exhib/aaa0074.htm

Also, the 6C8G tends to be confused with some sort of a 6SL7 predecessor for some weird reason - despite having a twice smaller amplification factor.

It's somewhat in between SN7 and SL7 but could have well been the predecessor of the 6SL7. The 26 (->27 -> 37 -> 76 ->) was the predecessor of the 6J5 despite being a very much different tube (with half the gain).

 

[mordy]

Thanks @mordy; for this.

They don't only sound similar. They were also build very similar. Could have been the same production line on a different day. Most of my 6F8G and 6C8G look alike when from the same manufacturer.

Here's an example from a National Union tube type 6F8G and 6C8G. Both carry the same base (with date code 1U) and very much similar internal construction.
And here's a link to a 6J5 with a similar internal structure: http://www.r-type.org/exhib/aaa0074.htm



It's somewhat in between SN7 and SL7 but could have well been the predecessor of the 6SL7. The 26 (->27 -> 37 -> 76 ->) was the predecessor of the 6J5 despite being a very much different tube (with half the gain).

Based on some National Union tubes that I have, I think that the date code IU is June 1945.

 

[triod750]

Based on some National Union tubes that I have, I think that the date code IU is June 1945.

Well, @mordy, what does then 'EN' mean? Please? 6F8G.

 

[mordy]

Well, @mordy, what does then 'EN' mean? Please? 6F8G.

This is an educated guess regarding the month(s). The first letter is the year, and the second letter probably a sequence of months, perhaps a quarter of the year. It is possible that the second letter, designating the months, changed for different years.
E = 1941
N = possibly March /April/ May
Here is a list of the the first letters designating the year for National Union tubes from the 40's:
D =1940
E = 1941
F = 1942
G = 1943
H = 1944
I = 1945
J = 1946
Here is a source: https://audiokarma.org/forums/index.php?threads/1940s-national-union-date-codes.763037/

 

[triod750]

This is an educated guess regarding the month(s). The first letter is the year, and the second letter probably a sequence of months, perhaps a quarter of the year. It is possible that the second letter, designating the months, changed for different years.
E = 1941
N = possibly March /April/ May
Here is a list of the the first letters designating the year for National Union tubes from the 40's:
D =1940
E = 1941
F = 1942
G = 1943
H = 1944
I = 1945
J = 1946
Here is a source: https://audiokarma.org/forums/index.php?threads/1940s-national-union-date-codes.763037/

Let's say May, so I will celebrate 60 years this month. I wish I was that young!

 

[tubebuyer2020]

It's somewhat in between SN7 and SL7 but could have well been the predecessor of the 6SL7. The 26 (->27 -> 37 -> 76 ->) was the predecessor of the 6J5 despite being a very much different tube (with half the gain).

Maybe, but I doubt it. I mean take 12AU7, 12AV7, 12AY7, 12AX7, 12AT7 - all are just different tubes with different amplification factors serving their purposes.

If I had to nominate a tube to be a predecessor of 6SL7 it would be 6F5G, it's a single triode but it has an amplification factor of 100 like 12AX7.

 

[Velozity]

The GEC L63 sounds killer in any scenario. Here's a fun setup I just put together to use on my work desk. The L63 are almost worth more than everything else pictured, LOL (except the Fivre 6V6G power tubes of course). This setup sounds waaaaaay better than I thought it would. I'm going to have fun rolling 6J5 + 6V6 combos with this. Shout out to @Deyan for the quick adapter work!

 

[Slade01]

The GEC L63 sounds killer in any scenario. Here's a fun setup I just put together to use on my work desk. The L63 are almost worth more than everything else pictured, LOL (except the Fivre 6V6G power tubes of course). This setup sounds waaaaaay better than I thought it would. I'm going to have fun rolling 6J5 + 6V6 combos with this. Shout out to @Deyan for the quick adapter work!

I must say, that is the first time I've seen a car stereo repurposed like that - really creative - pretty freaking cool. That looks like a fun setup for sure.

 

[Velozity]

I must say, that is the first time I've seen a car stereo repurposed like that - really creative - pretty freaking cool. That looks like a fun setup for sure.

Thanks! I'm actually planning to make some wooden side and top panels to screw into the chassis of the Alpine. That should take the coolness factor up a notch . It's been collecting dust in my garage for 5 years. I think I only paid like $25 for it but it works great and gives me CD/AUX/iPod/FM. It's being powered by an AC/DC adapter from an old cable box that happens to output 12V. Perfect!