[mordy]

people ... WARNING!

I discoverd something not nice about C3g with our LD... at least with LDII (last hardware version)... unsing the adapter C3g works with LDII but works badly, if you measure the voltage at the heaters pins you discover that it is only 5,7V instead of the NOT lower then 6,0V admitted

from where this behaviour? from the C3g that has a heater current load of 390mA (each) against the nominal load of 175mA of a 5654... in practice the load is the double and the transformer, at that output, collapse

what is the problem? the problem is that a underpowerd heater can cause a shortening of the tube life down to few hours instead of the expected 10.000... and C3g are rare and expensive!

at the moment I replace the C3g with the 6HM5, that unfortunately are quite far to be the same, waiting to modify those adapters I've done for the C3g to be able to power those heaters with an external linear power supply (probably based on LM317 or 7805)

to better understand about underpowered heaters:
https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-3.html
https://audioxpress.com/article/the-internal-life-of-vacuum-tubes

I cannot speak from a scientific point of view, but based on my understanding tolerances up to 10% are acceptable in tube manufacturing. In addition, the electric grid itself is almost never spot on and voltages vary there as well; it is almost never exactly 120/220V etc.
The C3g tubes were developed for underwater transatlantic telephone cable transmissions and must have been made for rugged use. The glass is tempered to withstand pressure (although fragile when "rolling" the tube). 10% of 6.3V = 5.67V.
However, if the manufacturer's spec sheet specifies other voltage limits that takes precedence.
The C3g tube has a life span in excess of 10,000 hours - I am not aware of tube failures.

 

[Jolterrrr]

Hello! I've recently joined after lurking this thread for a while because I have some questions to ask about my Little Dot II. I've been enjoying it recently with Sylvania 6SN7 power tubes and Mullard EF92 driver tubes, and im loving this setup. I also have some Voshkod drivers coming in soon, excited to try those. However, I do have one issue.

When I was first setting up my LD, I was struggling to find out how to open it to change the internal dip switches, and I tried removing the front panel. This damaged the volume potentiometer, and now the LD can only go to about 20% volume before the right channel cuts out completely. The knob can also rotate a full 360 degrees (which I havent done while its powered on). I've looked into this and have heard about people replacing the potentiometer with an Alps Blue 100k, should I do this? I have a friend who's experienced in electronics and soldering, I just want to be sure that theres not another easier solution to my problem.

I've been circumventing this issue by using the LD as a pre-amp and raising the volume through my FiiO K5, but I'd like to just fix the issue anyway so I wont have to worry about whether or not its causing distortion or something.

Thank you!

I use Sylvania 6SN7 Also with pair of Siemens c3g and pair of lorenz c3g. Buy those and you Will be happy! Trust me

 

[lupoal]

@mordy ... we have the same point of view but, unfortunately, in Siemens, or Lorentz etc, data sheet is clearly specified that the heater MUST work in the range 6,3 +/- 5%... that means from 6 to 6,7... and that sound strange to me too as the main power supply is never 230Vac ... in my case is almost all the time around 223, but can also be 240, but in both cases is roughly 5%

to be honest I’m quite annoyed by this fog around tubes and how to properly use them... somebody says “don’t worry” somebody else “are you crazy? That will destroy them in short time” ... is It possible doesn’t exist a single true rule? Uff

 

[mordy]

@mordy ... we have the same point of view but, unfortunately, in Siemens, or Lorentz etc, data sheet is clearly specified that the heater MUST work in the range 6,3 +/- 5%... that means from 6 to 6,7... and that sound strange to me too as the main power supply is never 230Vac ... in my case is almost all the time around 223, but can also be 240, but in both cases is roughly 5%

to be honest I’m quite annoyed by this fog around tubes and how to properly use them... somebody says “don’t worry” somebody else “are you crazy? That will destroy them in short time” ... is It possible doesn’t exist a single true rule? Uff

Very hard to find the real truth, but over the years I have not come across people complaining that the C3g tubes blew up or were short lived, so based on that I personally would not worry. But that is only my personal feeling and if you are worried you should not rely on that. Again, experience has not showed that the C3g tubes have problems.
Here is my favorite tube photo - a C3g without the shield at 425V plate current:

I believe that the blue color comes from a Beryllium getter.

 

[gibosi]

@mordy ... we have the same point of view but, unfortunately, in Siemens, or Lorentz etc, data sheet is clearly specified that the heater MUST work in the range 6,3 +/- 5%... that means from 6 to 6,7... and that sound strange to me too as the main power supply is never 230Vac ... in my case is almost all the time around 223, but can also be 240, but in both cases is roughly 5%

to be honest I’m quite annoyed by this fog around tubes and how to properly use them... somebody says “don’t worry” somebody else “are you crazy? That will destroy them in short time” ... is It possible doesn’t exist a single true rule? Uff

Well, if you were going to install them into an underwater transatlantic telephone cable transmission system and run them 24 hours a day, for a very long time, then yes, it would be most wise to follow the data sheet. But in your application if the heater voltage is a bit low or high, it's not going to make a measurable difference. My advice, relax and enjoy these tubes.

 

[lupoal]

yes, I have the same opinion about... I'm just a little scared by this diagram

https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-post3012333.html

well, in the same thread there are more then one guy with doubts about that... I was wondering if the writer is another hi-fi guru declaring strange things... it would be interesting to find that RCA document, just for personal knowledge

here I founded another discussion about ... I still have to read it, so just for info https://groupdiy.com/threads/reduced-filament-voltage.32746/

@mordy the C3g without housing is really nice!

 

[Jolterrrr]

yes, I have the same opinion about... I'm just a little scared by this diagram



https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-post3012333.html

well, in the same thread there are more then one guy with doubts about that... I was wondering if the writer is another hi-fi guru declaring strange things... it would be interesting to find that RCA document, just for personal knowledge

here I founded another discussion about ... I still have to read it, so just for info https://groupdiy.com/threads/reduced-filament-voltage.32746/

@mordy the C3g without housing is really nice!

You worry to much.

 

[lupoal]

... ok

 

[TrollDragon]

yes, I have the same opinion about... I'm just a little scared by this diagram



https://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-bad-ugly-post3012333.html

well, in the same thread there are more then one guy with doubts about that... I was wondering if the writer is another hi-fi guru declaring strange things... it would be interesting to find that RCA document, just for personal knowledge

here I founded another discussion about ... I still have to read it, so just for info https://groupdiy.com/threads/reduced-filament-voltage.32746/

@mordy the C3g without housing is really nice!

The first thing to keep in mind in these other threads is that most of the discussion is based around guitar amps that have power tubes. The amplifiers we use are preamps that have no power output section.

From that same thread on diyaudio post #53

This is why amps such as Scott, Fisher and such, which routinely ran 12AX7s (nominally 12.6v heaters) at 11v, sometimes even lower, work as well as they do. If the tube that can deliver 1.25ma, is only being asked to deliver .3ma current... then there is NO PROBLEM. In many phono and input preamp sections, this is the case!

You would have to do the math using the LD MK2 input circuit components and C3g to see if this is the case or not...

 

[lupoal]

You would have to do the math using the LD MK2 input circuit components and C3g to see if this is the case or not...

unfortunately I'm not able...

in any case a man in another forum pointed something interesting... it is not only a matter if the tube will lst longer or die earlier, it is also the fact that if that part of the transformer should, and do normally that, supply 6,3Vac when we see it collapsing down to 5,7V it means that the transformer in overloaded... the tube underpowered maybe will live two times longer in a LD2 condition... but the transformer?

 

[triod750]

unfortunately I'm not able...

in any case a man in another forum pointed something interesting... it is not only a matter if the tube will lst longer or die earlier, it is also the fact that if that part of the transformer should, and do normally that, supply 6,3Vac when we see it collapsing down to 5,7V it means that the transformer in overloaded... the tube underpowered maybe will live two times longer in a LD2 condition... but the transformer?

Does your amp with its tubes sound good to you?

(I have stopped trying to understand electric matters and this has made life easier for me. But there is nothing wrong in trying to understand and being pro-active).

 

[lupoal]

... yes I like how it sounds... but, for example, not all the times with all the possible mix I can arrange with the tubes I have...

my target is not to understand the concept of “infinite” or the meaning of the life but if, as it is now, it can be set to work better or if, as it is, it is already fine and safe... if there is something wrong that I can fix, if there is something I could improve without looking for Boson X ... I’m not looking for anything absurd, I will never buy a power cord at 4000 euro per meter... but this rolling tube fun sometimes could look approached in a little too easy way... just doubts, nothing serious

but i agree with you... knowledge is not, most of the time, the way to happiness ... but is that transformer overloaded or not?

 

[Jolterrrr]

... yes I like how it sounds... but, for example, not all the times with all the possible mix I can arrange with the tubes I have...

my target is not to understand the concept of “infinite” or the meaning of the life but if, as it is now, it can be set to work better or if, as it is, it is already fine and safe... if there is something wrong that I can fix, if there is something I could improve without looking for Boson X ... I’m not looking for anything absurd, I will never buy a power cord at 4000 euro per meter... but this rolling tube fun sometimes could look approached in a little too easy way... just doubts, nothing serious

but i agree with you... knowledge is not, most of the time, the way to happiness ... but is that transformer overloaded or not?

Unrelated. But have you tried hardware EQ your sound going into your dotty? I bought this one and now everything is perfect

Leicozic Dual 31 Bands Equaliser Digital Equalizador De Audio Equalizers A3 Profesional Sound System Stage & Karaoke Equipment
https://a.aliexpress.com/_mql6Gyt

 

[triod750]

... yes I like how it sounds... but, for example, not all the times with all the possible mix I can arrange with the tubes I have...

my target is not to understand the concept of “infinite” or the meaning of the life but if, as it is now, it can be set to work better or if, as it is, it is already fine and safe... if there is something wrong that I can fix, if there is something I could improve without looking for Boson X ... I’m not looking for anything absurd, I will never buy a power cord at 4000 euro per meter... but this rolling tube fun sometimes could look approached in a little too easy way... just doubts, nothing serious

but i agree with you... knowledge is not, most of the time, the way to happiness ... but is that transformer overloaded or not?

I know naathing about my transformer and even less about your transformer. My runs cool with most tubes. It runs much hotter with 6N6P than with 6SN7 or 6H12C for example. With 6BX7, 6BL7, A2293 and tubes of that kind I use an external psu. A2293, 6080 and 6AS7G generate a lot of heat and I don't expect them to be kind to the innards of any Small Dot. The other tubes mentioned give me no worries.

Right now I am listening to GE 5687 as outputs with a dual triode ECC82/12AU7 (Telefunken) as input. I believe the 5687 runs cooler than 6N6P, maybe because it uses an adapter that isolates it from the chassis. I have found the GE 5687 somewhat recessed previously, distant as I commented to Itzi. Since I find TFK ECC82/12AU7 a little on the bright side I wanted to check this combination. I think the TFK made the GE better to my ears. I will try a Philips 12AU7 later. These 12AU7 are tubes I already had. They are tubes that can be expensive today, at least as NOS. But who needs NOS? Use NOS tubes for a while and they are not NOS anymore. Are they less good then?

 

[lupoal]

Ok, I missed the point about NOS or NOT NOS anymore (sound like ... to be or not to be... )

I will touch my transformer... unfortunately is not sexy at all