The Reference 6SN7 Thread

[BrainSalat]

You can swap a 6n8s for the 1578, basically that is the same tube. 1578 just means the triodes are well matched according to many. I may get back to you later, I am in the process of getting a possible torn retina checked out in an hour or so. I may be out of commission for a few days.

Thanks @Paladin79 for the quick reply and good luck in the doc.

 

[Paladin79]

Best of luck with your eye @Paladin79 !

Thanks, they do not believe it is is a tear and will monitor my right eye for a couple weeks. Now comes a major headache from having my pupils dilated twice today lol.

 

[jonathan c]

Thanks, they do not believe it is is a tear and will monitor my right eye for a couple weeks. Now comes a major headache from having my pupils dilated twice today lol.

… sunglasses & staying inside?

 

[Paladin79]

… sunglasses & staying inside?

Yep lol

 

[David A Silva]

Yep lol

Good news, congrats... I hate getting eyes dilated... Time to break out the headphones!

 

[BrainSalat]

You can swap a 6n8s for the 1578, basically that is the same tube. 1578 just means the triodes are well matched according to many. I may get back to you later, I am in the process of getting a possible torn retina checked out in an hour or so. I may be out of commission for a few days.

So in the meantime I performed the test mixing the 1578 with 6N8S and both of the 1578 tubes produced the hum separated, so now I heard the hum only on the left side (L:1578#1, R:6N8S) and then only on the right side (L:6N8S, R:1578#2). That should mean something, how can be a coincidence?

 

[Paladin79]

So in the meantime I performed the test mixing the 1578 with 6N8S and both of the tubes produced the hum separated, so now I heard the hum only on the left side (L:1578#1, R:6N8S) and then only on the right side (L:6N8S, R:1578#2). That should mean something, how can be a coincidence?

Some amps do not like Russian tubes, they are dead silent with no signal in amps I designed.

 

[TLO]

So in the meantime I performed the test mixing the 1578 with 6N8S and both of the tubes produced the hum separated, so now I heard the hum only on the left side (L:1578#1, R:6N8S) and then only on the right side (L:6N8S, R:1578#2). That should mean something, how can be a coincidence?

If you run out of ideas, try this....
With the amp running, hold the glass tube of the 1578 with your hand (of course wearing a glove) and see if the hum goes away.
If so, you are in luck...the hum is due to EMI then. You can try with a sheet of baking aluminum foil, roll it into a cylinder (try single or multi layers), then cover the whole tube with the bottom touching the chassis. If this works, you can replace it with a nice looking copper braid.

 

[TLO]

Is that you, @Paladin79 ?

 

[sam6550a]

Is that you, @Paladin79 ?

He has a warehouse of type 851, which is even larger than this tube.

 

[sam6550a]

He has a warehouse of type 851, which is even larger than this tube.

Just in case you are curious, see https://frank.pocnet.net/sheets/141/g/GL851.pdf

 

[BrainSalat]

If you run out of ideas, try this....
With the amp running, hold the glass tube of the 1578 with your hand (of course wearing a glove) and see if the hum goes away.
If so, you are in luck...the hum is due to EMI then. You can try with a sheet of baking aluminum foil, roll it into a cylinder (try single or multi layers), then cover the whole tube with the bottom touching the chassis. If this works, you can replace it with a nice looking copper braid.

Unfortunately this didn't work either. No idea what else could I try. I have re-soldered the pins twice and the hum didn't change at all. I found interesting the both tubes have the same level of hum, which made me think that probably the tubes work as designed but for some unknown reason the Euforia amp doesn't like them, but in the Euforia thread you can read many people have tried these tubes before with the Euforia. I ran out of ideas. The seller wrote me the following (something I could not verify/reject myself):

"The probable reason is the high filament current, 6n8s, like the full analog 6sn7, are powered by 8-9ma current, but for example 6sn7gt, 6sn7gtb and others can be powered by current up to 20ma. With a high current, 6n8s sounds good and provocatively, but not for long, for it this is an extreme operating mode. Some tubes tolerate overloads well, so designers increase the current to achieve a good sound. It is often written on the forums that when the tube is replaced, the sound quality increases, but this should be accompanied by an appropriate adjustment of the amplifier"

 

[sam6550a]

Unfortunately this didn't work either. No idea what else could I try. I have re-soldered the pins twice and the hum didn't change at all. I found interesting the both tubes have the same level of hum, which made me think that probably the tubes work as designed but for some unknown reason the Euforia amp doesn't like them, but in the Euforia thread you can read many people have tried these tubes before with the Euforia. I ran out of ideas. The seller wrote me the following (something I could not verify/reject myself):

"The probable reason is the high filament current, 6n8s, like the full analog 6sn7, are powered by 8-9ma current, but for example 6sn7gt, 6sn7gtb and others can be powered by current up to 20ma. With a high current, 6n8s sounds good and provocatively, but not for long, for it this is an extreme operating mode. Some tubes tolerate overloads well, so designers increase the current to achieve a good sound. It is often written on the forums that when the tube is replaced, the sound quality increases, but this should be accompanied by an appropriate adjustment of the amplifier"

That makes no sense at all. 6SN7 and 6n8s are both rated at a filament current of 600ma, and most tube manufacturers say this is plus or minus 5%. The 6n8s data sheet says +60 -50 ma, which is about the same. You will get a bigger deviation from line voltage variation. I have no idea what "8-9ma" means, but no heaters are that close. I have never heard of "tuning" the filament voltage or current to tweak an amplifier. Since you have resoldered the pins, and believe that the hum is one section in each tube, then the tube has heater cathode leakage, which occurs after many hours of use or by being used in a circuit that has high potential difference between the heater and cathode. The limit is 200v peak for the 6SN7GTA and 100v for the 6n8s [data sheet does not say peak or average]. Of course, the circuit topology dictates whether or not this leakage will be a problem. I would think this guy is mixing filament current and plate current in an attempt to obfuscate the problem that you have defective tubes.

 

[TLO]

Unfortunately this didn't work either. No idea what else could I try. I have re-soldered the pins twice and the hum didn't change at all. I found interesting the both tubes have the same level of hum, which made me think that probably the tubes work as designed but for some unknown reason the Euforia amp doesn't like them, but in the Euforia thread you can read many people have tried these tubes before with the Euforia. I ran out of ideas. The seller wrote me the following (something I could not verify/reject myself):

"The probable reason is the high filament current, 6n8s, like the full analog 6sn7, are powered by 8-9ma current, but for example 6sn7gt, 6sn7gtb and others can be powered by current up to 20ma. With a high current, 6n8s sounds good and provocatively, but not for long, for it this is an extreme operating mode. Some tubes tolerate overloads well, so designers increase the current to achieve a good sound. It is often written on the forums that when the tube is replaced, the sound quality increases, but this should be accompanied by an appropriate adjustment of the amplifier"

Another thought is perhaps this particular tube is more sensitive to micro-vibration due to current flow. Do you hear a louder tapping sound when you tapped lightly on the glass with a pen or even your finger nail compared to other tubes you have? I have a couple of tubes that has this characteristic, you could say it is the early stage of becoming what we called microphonic. Anyway, all tubes have some levels of being microphonic, the question is how much, will it affect the listening experience?
AFAIK, there is no solution to this problem. The best you can do is try it on different locations on the amp if your amp uses more than 1 6SN7 or on another amp.

 

[BrainSalat]

That makes no sense at all. 6SN7 and 6n8s are both rated at a filament current of 600ma, and most tube manufacturers say this is plus or minus 5%. The 6n8s data sheet says +60 -50 ma, which is about the same. You will get a bigger deviation from line voltage variation. I have no idea what "8-9ma" means, but no heaters are that close. I have never heard of "tuning" the filament voltage or current to tweak an amplifier. Since you have resoldered the pins, and believe that the hum is one section in each tube, then the tube has heater cathode leakage, which occurs after many hours of use or by being used in a circuit that has high potential difference between the heater and cathode. The limit is 200v peak for the 6SN7GTA and 100v for the 6n8s [data sheet does not say peak or average]. Of course, the circuit topology dictates whether or not this leakage will be a problem. I would think this guy is mixing filament current and plate current in an attempt to obfuscate the problem that you have defective tubes.

Thanks @sam6550a for the info. I will transmit him your thoughts.
Actually the tubes came with this data sheet (in russian) and seems he, with the 8-9[mA], was referring to the anode current:
Using google translate:
- Heater Voltage: 6.3 V
- Filament current: 550-660 mA.
- Voltage Anode: 250 V.
- Grid Voltage: -8 V
- Anode current: 5-13 mA
- Gain: 18-25