Hi,
This has been discussed here before although probably burried in various threads left and right.
So here goes:
Too high a heater voltage will exhaust cathode emission (very) rapidly so that's no good as you're wasting tubes and the curves will change as well.
With reduced heater voltage you'll prolong tubelife drastically (more than double it in the case of small signal tubes) while still have the same characteristics as if you'd stick with the 6.3V.
According to manufacturer recommendations one can go either low or high on 6.3V by 10%, in practice I wouldn't go below 6V which is great as it allows the use of a vast number of common 6V regulators.
5.7V is still safe but I've no idea how that will turn out in every day use. Maybe something to try in a phonopreamp perhaps?
Cheers,
This has been discussed here before although probably burried in various threads left and right.
So here goes:
Too high a heater voltage will exhaust cathode emission (very) rapidly so that's no good as you're wasting tubes and the curves will change as well.
With reduced heater voltage you'll prolong tubelife drastically (more than double it in the case of small signal tubes) while still have the same characteristics as if you'd stick with the 6.3V.
According to manufacturer recommendations one can go either low or high on 6.3V by 10%, in practice I wouldn't go below 6V which is great as it allows the use of a vast number of common 6V regulators.
5.7V is still safe but I've no idea how that will turn out in every day use. Maybe something to try in a phonopreamp perhaps?
Cheers,
Hi,
They'll have to or the voltage will be too low....
Depending on the xformer, the only problem you could face is overvoltage of the heater(s).
Note: we're sticking to normal heaters here of the variety used in tube such as 12AX7s and the like, not types for series heating as commonly used in TV sets.
Cheers,
They'll have to or the voltage will be too low....
Depending on the xformer, the only problem you could face is overvoltage of the heater(s).
Note: we're sticking to normal heaters here of the variety used in tube such as 12AX7s and the like, not types for series heating as commonly used in TV sets.
Cheers,
fdegrove said:
Thanks for the information. This reduced voltage is measured in my phono stage (Hagerman Cornet), having a pair of 12AX7s and a 12AU7 buffer. The 5Y3 rectified B+ is also somewhat lower voltage than what the schematic would require. I'm going to change a power resistor to increase the filament voltage. The B+ will have to remain as is.
An alternate idea is to use the 110 or 100vac primary taps on my transformer rather than the 120vac taps. This should increase the voltage on all secondary windings but will it cause the tranny to run hot? (Hammond 370BX)
By the way, my system sounds great as it is now. I'm curious however to see if I detect a sonic change with the proper heater voltage.
-S
Filament voltage update:
I changed out a resistor and now measure 6.2 volts on the heaters.
Just listened to three hours of great LP music. I definitely have increased gain in my phono stage now since I need to turn down the volume on my preamp to maintain similar spl. Overall there is a greater weight to the music and better balance top to bottom. The RIAA function may be more accurate with the gain tubes functioning at their rated heater voltage. My phono stage is delivering much better “punch” to the music (for lack of a better word, you know what I mean).
12A_7 tubes sound wonderful in the right circuit. Others have built octal-based Cornet phono stages and have experienced great results too albeit using higher output cartridges and/or step-up transformers.
-S
I changed out a resistor and now measure 6.2 volts on the heaters.
Just listened to three hours of great LP music. I definitely have increased gain in my phono stage now since I need to turn down the volume on my preamp to maintain similar spl. Overall there is a greater weight to the music and better balance top to bottom. The RIAA function may be more accurate with the gain tubes functioning at their rated heater voltage. My phono stage is delivering much better “punch” to the music (for lack of a better word, you know what I mean).
Sch3mat1c said:
12A_7 tubes sound wonderful in the right circuit. Others have built octal-based Cornet phono stages and have experienced great results too albeit using higher output cartridges and/or step-up transformers.
-S
fdegrove said:Hi,
According to manufacturer recommendations one can go either low or high on 6.3V by 10%, in practice I wouldn't go below 6V which is great as it allows the use of a vast number of common 6V regulators.
5.7V is still safe but I've no idea how that will turn out in every day use. Maybe something to try in a phonopreamp perhaps?
Cheers,
Hi
NEVER go below -5% of nominal spec, Tube life decreases drastically once below 6.0V (in the case of E type tubes). I learned this from an old master who engineered tubes at Mullard. Better stick to their wisdom.
Sonically some tubes start to sound significantly less when deviating from nominal.
my 2 cts
Hi,
Ir. van Mossevelde?
I suppose we have the same source of wisdom, Guido: Audio Discussions as published by A&T...
IIRC you were present when this was discussed among other related topic.
My documents from Belgian Philips licensee MBLE confirm this BTW.
When nominal heater voltage is 6.3V going below 6V doesn't allow for the cathode to reach operational temperature and causes cathode poisoning.
Cheers,
Ir. van Mossevelde?
I suppose we have the same source of wisdom, Guido: Audio Discussions as published by A&T...
IIRC you were present when this was discussed among other related topic.
My documents from Belgian Philips licensee MBLE confirm this BTW.
When nominal heater voltage is 6.3V going below 6V doesn't allow for the cathode to reach operational temperature and causes cathode poisoning.
Cheers,
Hi,
Guido,
I wouldn't mind doing the translation of the document or at least a decent summary of it.
Knowing you have been an actual witness would be a great plus as some of the taped stuff is rather err....funny.
Either way, if you're interested just let me know and I'll schedule it for one of our long winterdays...
Cheers,
Guido,
I wouldn't mind doing the translation of the document or at least a decent summary of it.
Knowing you have been an actual witness would be a great plus as some of the taped stuff is rather err....funny.
Either way, if you're interested just let me know and I'll schedule it for one of our long winterdays...
Cheers,
fdegrove said:Hi,
Guido,
I wouldn't mind doing the translation of the document or at least a decent summary of it.
Knowing you have been an actual witness would be a great plus as some of the taped stuff is rather err....funny.
Either way, if you're interested just let me know and I'll schedule it for one of our long winterdays...
Cheers,
Hi Frank
That would be great, however the copyright is at Audio en Techniek so we have to discvuss with them
cheers
Guido
I know this is an old thread but I have a question. I'm building a line preamp using 6N6P triodes. I used Schottky diodes and a pi filter. Originally I had 7.4 volts with a .1 ohm resistor in the filter. So I added a 1 ohm resistor after the filter and now have 5.96 volts @ 1.54 amps for two tubes. Spec is 6.3 volts and 1.5 amps (for two tubes). Is that close enough? Its only .27 watts different from ideal.
Here is interesting graph (right), dependence of anode current, transconductance, and G2 current, on filament voltage for 6P15P video pentode. I would assume 5.5V regulated is fine.
An externally hosted image should be here but it was not working when we last tested it.
Since it's not a regulated filament supply I would trim for close to 6.3V at your nominal line voltage. We are probably talking something around 10 ohms parallel with the 1 ohm.
The 6N6 will tolerate 5.7V - 6.9V in normal operation according to the data sheet, so in theory this is fine. (I would be inclined to tweak a bit..)
The 6N6 will tolerate 5.7V - 6.9V in normal operation according to the data sheet, so in theory this is fine. (I would be inclined to tweak a bit..)
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