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Old 26th August 2004, 05:40 AM   #1
shif is offline shif  United States
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Default Filament voltage ?

What are the effects of using a vacuum tube (9 pin dual triode) operating at reduced filament voltage, say 5.7 volts rather than 6.3?

Sonic degradation?
Reduced dynamics?
Reduced tube life?

Just curious...


-S
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Old 27th August 2004, 02:53 AM   #2
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Hi,

Quote:
What are the effects of using a vacuum tube (9 pin dual triode) operating at reduced filament voltage, say 5.7 volts rather than 6.3?
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,
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Old 27th August 2004, 03:17 AM   #3
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How about amperage? Do the heaters draw what they need? If I have a tranny with higher amperage heater outputs than the tube being heated needs, is that a problem? Thanks.
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Old 27th August 2004, 03:36 AM   #4
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Hi,

Quote:
How about amperage? Do the heaters draw what they need?
They'll have to or the voltage will be too low....

Quote:
If I have a tranny with higher amperage heater outputs than the tube being heated needs, is that a problem?
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,
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Old 27th August 2004, 04:44 AM   #5
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Frank, FWIW, the classic Berning TF10 used a pair of 12V heaters in series, fed by 22V. Ran cool, great tube life, as you said. Dave Berning felt that bringing the heater voltage up to nominal (25.2V) made the sound too bright.
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Old 27th August 2004, 05:01 AM   #6
shif is offline shif  United States
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Quote:
Originally posted by fdegrove

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?
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.

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Old 27th August 2004, 10:43 AM   #7
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Quote:
Originally posted by shif
Thanks for the information. This reduced voltage is measured in my phono stage (Hagerman Cornet), having a pair of 12AX7s and a 12AU7 buffer.
Oh noes!!!! Don't mention 12 ax ANYTHING in FRANK'S PRESENCE!

Rumble....oh no...... it's on its way............. rumble rumble..... coming closer..............!!!!!!!!!!!!!!





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Old 27th August 2004, 12:52 PM   #8
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Hi,

Quote:
Oh noes!!!! Don't mention 12 ax ANYTHING in FRANK'S PRESENCE!
It's all in your head...

Quote:
Dave Berning felt that bringing the heater voltage up to nominal (25.2V) made the sound too bright.
That could circuit-dependent perhaps, not sure.
I do recall ARC going off the deep end with heater overvoltage on some preamps, they sure wised up later on...

Cheers,
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Old 28th August 2004, 06:47 AM   #9
shif is offline shif  United States
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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).

Quote:
Originally posted by Sch3mat1c

Oh noes!!!! Don't mention 12 ax ANYTHING in FRANK'S PRESENCE!
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.



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Old 28th August 2004, 09:42 PM   #10
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Quote:
Originally posted by fdegrove
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
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