[jamato8]

I have found that while tubes can be forgiving and you can use with an adapter, which I made like 12 years ago, a 12SL7 in place of a  12AX7 and a 12SN7 in place of a 12AU7, if bias and plate voltages are "really" optimized, you are not going to hear the truth of what each tube can deliver. I have used the 76 and only after getting the bias and plate voltage exactly tuned, the sound wasn't everything that the 76 could deliver. I used high quality pots and then replaced them with good resistors. I also found that battery bias, IMO, is better than anything else. 

 

[Skylab]

Maybe it sounds better precisely BECAUSE the bias is incorrect?

I believe you hit the nail on the head here. Understanding that "better" is of course subjective...a tube used a little outside its ideal parameters will very often add increased amounts of second order harmonic distortion, which most humans, your truly included, find pleasing, to a point.

 

[hypnos1]

I believe you hit the nail on the head here. Understanding that "better" is of course subjective...a tube used a little outside its ideal parameters will very often add increased amounts of second order harmonic distortion, which most humans, your truly included, find pleasing, to a point.

 
Could well indeed be something in what gibosi says...although I'm wondering whether other elements in the system also have a bearing on just how much these variations from optimum affect final outcome - for better or worse!
 
In my own case, for example, ECC31s (common-cathode version of the 32, which you probably already know, lol!) perform very well in my 6SN7-driven Feliks-Audio Elise OTL amp. But real magic has only just appeared with my new tube DAC - using Tesla E88CCs (gold pins and grid posts) - in place of my also ESS Sabre 9018-clad Audiolab 8200CD. The difference is not minimal...I can now appreciate why these Mullards - either 31/32 or CV181 are so highly regarded and sought after...even if their prices are indeed now rather OTT!!
 
This aspect of tube/equipment 'synergy' certainly does appear to inhabit the realms of pure Alchemy, methinks!
 
ps. This 'magic' is also, no doubt, aided and abetted by my GEC CV2523s and Beyer T1s, lol...the latter for which I must thank you, as your past glowing comments on these headphones helped convince me to spend far more than I ever anticipated on cans, and have proved to be worth every penny...as others also found thereafter with their Elises...

...

 

[vintinfinity]

Got myself a Sylvania 6sn7 GTA L2B to roll with a BH Crack amp. Does anyone know what the L2B means?
 
Also, I thought these were the "Chrome Domes" I was told to look for. It does have chrome flashing over most of one side and the top. however, Another auction by the same seller says in the listing "I3B chrome-dome factory code"  I saw this after purchasing the L2B stamped versions.
 
Sounds great with a 5998 output tube. Instrumentation has a bit more of the 3d effect going on. Overall a bit less bass, but still good as compared to a late 70s coin base RCA GTB tube

 

[gibosi]

  Got myself a Sylvania 6sn7 GTA L2B to roll with a BH Crack amp. Does anyone know what the L2B means?
 
Also, I thought these were the "Chrome Domes" I was told to look for. It does have chrome flashing over most of one side and the top. however, Another auction by the same seller says in the listing "I3B chrome-dome factory code" (that is a capital i) I saw this afterwards. 

 
I assume "6SN7GTA" is etched on top inside of a hexagon and the letters "L2B" are etched under it? L = December, 2 = 1952 and some think the B = the manufacturing plant.
 
And "I3B" indicates a manufacturing date of August, 1953.
 
http://www.head-fi.org/t/479031/6sn7-tube-addicts/3855#post_10140637
 
Short bottles, very heavily chromed, both 6SN7GT and 6SNGTA, manufactured in the late 1940's and early 1950's, are Chrome Domes. From your description, it appears that you have the "real McCoy". 
 
http://www.head-fi.org/t/479031/6sn7-tube-addicts/5565#post_12340043

 

[vintinfinity]

   
I assume "6SN7GTA" is etched on top inside of a hexagon and the letters "L2B" are etched under it? L = December, 2 = 1952 and some think the B = the manufacturing plant.
 
And "I3B" indicates a manufacturing date of August, 1953.
 
http://www.head-fi.org/t/479031/6sn7-tube-addicts/3855#post_10140637
 
Short bottles, very heavily chromed, both 6SN7GT and 6SNGTA, manufactured in the late 1940's and early 1950's, are Chrome Domes. From your description, it appears that you have the "real McCoy". 
 
http://www.head-fi.org/t/479031/6sn7-tube-addicts/5565#post_12340043

 
yep, the date code is etched on below the tube model. cool, thanks for the info. I got a pretty good deal (compared to others on ebay) on a pair of them with different branding; one sylvania and one magnavox.

 

[whirlwind]

In general, I like Sylvania SN7 tubes....at least all of the ones that I have listened to.
 
Listening to the bad boy right now, and this tube tickles my funny bone....love it 

 

[DogMeat]

okay.
how do the 3 hole "Bad Boys" differ from a set of 3 hole "Chrome Domes"?
 
I am debating the purchase of CD's, matched circa '49 vs the purchase of a pair of the true 3 hole BB's.
 
I like my Syl sn7's also, got the Woo-made adaptors under them.
NICE sweet and tasty sound.
Bring MUCH to the T1 table.

 

[gibosi]

  okay.
how do the 3 hole "Bad Boys" differ from a set of 3 hole "Chrome Domes"?
 
I am debating the purchase of CD's, matched circa '49 vs the purchase of a pair of the true 3 hole BB's.
 
I like my Syl sn7's also, got the Woo-made adaptors under them.
NICE sweet and tasty sound.
Bring MUCH to the T1 table.

 
Good info here:
 
http://www.head-fi.org/t/117677/the-reference-6sn7-thread

 

[DogMeat]

ah yes.
had tuned in to the wrong-ish thread.
 
THANX!!!

 

[Jozurr]

So I just received a pair of ECC31 tubes. From what I understood, the ECC31 with an ECC31 to 6SN7 Adapter is essentially the same as ECC32, based on this post in the thread:
 
1) "The ECC32 and ECC31 are identical except that the ECC32 has separate cathodes"
 
2) And second, the correct cathode resistance for the ECC32 should be 1/2 to 2/3 that of a 6SN7. Well, it just so happens that tying the common cathode in an ECC31 to both 6SN7 cathodes in the socket reduces the cathode resistance by 1/2. As a result, it would appear that using such an adapter provides the ECC31 with the correct bias. On the other hand, simply sticking an ECC32 into a 6SN7 socket results in the cathode resistance being twice as high as it should be. 
 
 
I previously used the ECC32 in my Liquid Glass amp successfully. However, when I plug in the ECC31 with the ECC31 to 6SN7 adapter in the amp, the amp trips up. This is what the manufacturer had to say about the amp:
 
"Hi. The LG has an automatic shut off if the tube draws too much plate current. This protects the HV PS. This is probably what is happening.
 
Although the glass can handle a wide variety of tubes there are limits on heater current and plate current."
 
Anyone knows what's going on?

 

[gibosi]

  I previously used the ECC32 in my Liquid Glass amp successfully. However, when I plug in the ECC31 with the ECC31 to 6SN7 adapter in the amp, the amp trips up. This is what the manufacturer had to say about the amp:
 
"Hi. The LG has an automatic shut off if the tube draws too much plate current. This protects the HV PS. This is probably what is happening.
 
Although the glass can handle a wide variety of tubes there are limits on heater current and plate current."
 
Anyone knows what's going on?

 
The ECC31 and ECC32 have identical heaters, drawing about 0.95 amps, so I doubt very much that that is the reason. From their website, it appears that the LG employs special sensing circuitry to allow it to handle a wide variety of tubes. My best guess is that that even with an adapter, the common cathode in the ECC31 is simply too strange and as a result that circuitry shuts the LG down.
 
In more conventional amps, common-cathode double triodes, such as the ECC31, 6N7G and 6A6, with appropriate adapters, work fine.
 

 

[Jozurr]

   
The ECC31 and ECC32 have identical heaters, drawing about 0.95 amps, so I doubt very much that that is the reason. From their website, it appears that the LG employs special sensing circuitry to allow it to handle a wide variety of tubes. My best guess is that that even with an adapter, the common cathode in the ECC31 is simply too strange and as a result that circuitry shuts the LG down.
 
In more conventional amps, common-cathode double triodes, such as the ECC31, 6N7G and 6A6, with appropriate adapters, work fine.
 

 
 
Some more thoughts by the manufacturer:
 
"I see. This tube cannot work in the glass and will damage it. Please note in manual only tubes with pinouts like 6sn7 or 12au7. Even though you're adapting you cannot separate the cathodes. At least as I read the data sheet. OTOH the ecc32 has separate cathodes and can be mapped to 6sn7 pinouts." 
 
 

 

[gibosi]

  Some more thoughts by the manufacturer:
 
"I see. This tube cannot work in the glass and will damage it. Please note in manual only tubes with pinouts like 6sn7 or 12au7. Even though you're adapting you cannot separate the cathodes. At least as I read the data sheet. OTOH the ecc32 has separate cathodes and can be mapped to 6sn7 pinouts." 
 

 
As I read this, common-cathode tubes are definitely a no-go in the LG. However, if a tube has separate cathodes, using an adapter to reroute the pins to match the pinout of either a 6SN7 or 12AU7 seems to be OK. So for example, it should be possible to roll 12AH7 with an adapter (6SN7) or 5687 with an adapter (12AU7).
 
Good information for Liquid Glass owners...

 

[Jozurr]

   
As I read this, common-cathode tubes are definitely a no-go in the LG. However, if a tube has separate cathodes, using an adapter to reroute the pins to match the pinout of either a 6SN7 or 12AU7 seems to be OK. So for example, it should be possible to roll 12AH7 with an adapter (6SN7) or 5687 with an adapter (12AU7).
 
Good information for Liquid Glass owners...

 
I see. Disappointed that I cant use the ECC31. Guess Ill try and find an amp which can use all 6SN7 and the ECC31, which sounds as good as the LG.
 
Thanks for the help!