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Old 7th September 2005, 10:47 AM   #1
fred76 is offline fred76  Philippines
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Default grid batt bias on phono....

Hi folks,

Maybe by now most of you are aware of the Artemis Labs phonostage where the 6N1P input tube uses fixed grid batt bias:

http://www.artemislabs.com/docs/PL1_Manual_1.pdf


My phono preamp has 1.5V on the input tube's cathode, so it is possible for me to convert the cathode bias to grid batt bias (coin cell) and in effect delete the 330uF cathode byass cap...

The question is if it is also 'okay' to do this mod on the second stage too since it has the same 1.5V on the cathode with 330uF cathode bypass cap value for the cathode R? Or, is it a bad idea to use fixed grid bias just right after the Passive Eq between 2 stages? Plus, would it mess up the Riaa Eq?

Thanks for any responses.

br,
fred
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Old 7th September 2005, 11:26 AM   #2
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...maybe it's only my wrong opinion,
but I am afraid a battery, in a tube amp, will explode, sooner or later...
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Old 7th September 2005, 11:47 AM   #3
Zen Mod is offline Zen Mod  Serbia
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I prefer NiCd ditto in cathode ,mebbe with just a smidge of capacity in paralel
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Old 7th September 2005, 01:43 PM   #4
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Quote:
Or, is it a bad idea to use fixed grid bias just right after the Passive Eq between 2 stages

If you apply the bias through the same grid resistor it will have no effect upon the riaa accuracy. Artemis would have probably done it if they didn't use the cathode for NFB. A very cool circuit btw.



Quote:
but I am afraid a battery, in a tube amp, will explode, sooner or later
You may be mistaking tube amps with pipe bombs If the battery is in the grid circuit it will never explode. And it will have less sonic signature than in the cathode.
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Old 7th September 2005, 04:58 PM   #5
EC8010 is offline EC8010  United Kingdom
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If a tiny bit of heat (from the valves) made batteries explode, how would car manufacturers get away with putting the battery in the engine compartment?
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Old 7th September 2005, 06:07 PM   #6
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Quote:
Originally posted by EC8010
If a tiny bit of heat (from the valves) made batteries explode, how would car manufacturers get away with putting the battery in the engine compartment?
Different technology?
I suspect that batteries for cars has only the name in common with 1.5V stylos...
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Old 7th September 2005, 06:40 PM   #7
cerrem is offline cerrem  United States
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If you put the 1.5V cell at the input grid of your phono stage tube...Then you will have a DC offset on the coil...You would need a input coupling/blocking cap....or as in the case of Artemis, they used input transformer...
I still don't like the idea that Artemic has the battery in SERIES with the input signal current..... I use batteries as well but don't have them in SERIES with any signal current....

Chris
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Old 7th September 2005, 06:46 PM   #8
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by TheGatesOfFate
Different technology?
I suspect that batteries for cars has only the name in common with 1.5V stylos...
Agreed, different technology, but the point remains; with only a little care batteries in valve kit can be kept cool and explosions avoided.
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Old 7th September 2005, 08:28 PM   #9
fred76 is offline fred76  Philippines
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Quote:
If you apply the bias through the same grid resistor it will have no effect upon the riaa accuracy. Artemis would have probably done it if they didn't use the cathode for NFB. A very cool circuit btw.
Hi analog_sa,

Thanks for confirming that. My particluar phonostage is zero feedback all throughout, 3rd stage is a mu-follower type circuit (cathode output) - the lower triode acting as ccs w/ unbypassed cathode... Artemis' design seems to havea built-in linestage already (LC loaded 3rd stage with mild NFB), and is more suited to passive volume control units or low mu preamps. BTW, I believe the Artemis circuit is designed by John Atwood (One Electron). And yes, a batt on the cathode is much more colored sounding IME, almost like having a lytic cap placed there. AC modulation is said to be the culprit...

I'm going to use coin cells. Saves space since the actual phono chassis is small. Plus I have access to good coin cell holders with copper contacts and pins.

Quote:
If you put the 1.5V cell at the input grid of your phono stage tube...Then you will have a DC offset on the coil...You would need a input coupling/blocking cap....or as in the case of Artemis, they used input transformer...
Hi Chris,

Artemis' 'lower' phono model doesn't have any built in step-up/input transformer. You can use a cap across the input for capacitance loading (3M's Textool thingie), maybe that addresses the issue of DC offset?? Schematic here:

http://www.artemislabs.com/docs/PH1_Manual_1.pdf

fred
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Old 7th September 2005, 08:34 PM   #10
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Quote:
Originally posted by EC8010


Agreed, different technology, but the point remains; with only a little care batteries in valve kit can be kept cool and explosions avoided.

Yes, I agree with you.
Anyway I wrote that it maybe a my own (wrong) opinion.
I have no "feeling" with 1,5 bateries...I forgot them in remote controls and in every kind of devices. I'm sure to forget them also in a amp, and you know, this kind of batteries have short life...
I don't like to open(after months or years) an amp(or a remote control or a little radio) and see a "dirty white liquid" all around...
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