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Old 2nd April 2010, 03:13 AM   #1
mach1 is offline mach1  Australia
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Default Novel mode of lithium battery bias

I recently came accross a novel (I think !) way of battery biasing a grounded cathode stage which I believe is attributable to Thorsten.

Image 1 shows lithium bias applied conventionally in Thorsten's Toccata.

Image 2 show the alternative method applied in a TRAM linestage implementation.

Quire different and very interesting. Has anyone here tried it and compared it to the conventional method ?
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File Type: bmp lith1.bmp (11.8 KB, 440 views)
File Type: bmp lith2.bmp (44.6 KB, 398 views)
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Old 2nd April 2010, 06:10 AM   #2
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thats cool!
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Old 2nd April 2010, 06:25 AM   #3
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Hey Mach1,
Both are applications by Thorsten, the second one is what, as I believe has been recommending later. They have both been around for some years now.
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Old 2nd April 2010, 07:51 AM   #4
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Quote:
Originally Posted by mach1 View Post
I recently came accross a novel (I think !) way of battery biasing a grounded cathode stage which I believe is attributable to Thorsten.

Image 1 shows lithium bias applied conventionally in Thorsten's Toccata.

Image 2 show the alternative method applied in a TRAM linestage implementation.

Quire different and very interesting. Has anyone here tried it and compared it to the conventional method ?
The second one floats the whole battery with the signal. That may give some issues with the bulk capacitance of the battery to chassis or whatever. First circuit is better in that respect.

Also note that this way of biasing was in use before WWII (which was before Thorsten was born ). It went out of vogue when components for off-line power supplies became available and affordable.


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Old 2nd April 2010, 08:57 AM   #5
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In both setups, but mostly in figure 1, a small AC current is flowing through the battery via the grid leak resistor. As lithium batteries are primary batteries (non-rechargeable), they may show some less-than-desirable behavior in the form of LF voltage fluctuations. In figure 2, only the grid current (arguably negligible) is flowing through it, and for high frequencies it is bypassed. So I'd recommend the situation of figure two as well. A typical lithium battery is not bigger than, say, a foil coupling cap. I wouldn't worry too much about the capacitive coupling with the environment.

The pre-ww2 sets typically used a bias battery, from which the bias voltages were derived with voltage dividers. This battery was always supplying current, so it needed to be replaced periodically or the tubes would drift away from their normal bias point. The lithium battery only sees a negligible load and should last at least 10 years as it is used here.
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Old 2nd April 2010, 09:28 AM   #6
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In both setups, but mostly in figure 1, a small AC current is flowing through the battery via the grid leak resistor. As lithium batteries are primary batteries (non-rechargeable), they may show some less-than-desirable behavior in the form of LF voltage fluctuations. In figure 2, only the grid current (arguably negligible) is flowing through it, and for high frequencies it is bypassed. So I'd recommend the situation of figure two as well. A typical lithium battery is not bigger than, say, a foil coupling cap. I wouldn't worry too much about the capacitive coupling with the environment.

The pre-ww2 sets typically used a bias battery, from which the bias voltages were derived with voltage dividers. This battery was always supplying current, so it needed to be replaced periodically or the tubes would drift away from their normal bias point. The lithium battery only sees a negligible load and should last at least 10 years as it is used here.
Hi Timpert,

Good points. Probably good to bypass the battery with a large electrolytic in any case?

jd
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Old 2nd April 2010, 09:40 AM   #7
SY is offline SY  United States
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Quote:
Originally Posted by mach1 View Post
I recently came accross a novel (I think !) way of battery biasing a grounded cathode stage which I believe is attributable to Thorsten.
...
Quire different and very interesting. Has anyone here tried it and compared it to the conventional method ?
See "The EC8010 RIAA Stage" by the Dread Morgan Jones in "Valve Amplifiers." I tried this bias scheme when prototyping my phono stage and found no real advantage over LED bias.
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Old 3rd April 2010, 05:25 AM   #8
mach1 is offline mach1  Australia
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Yes,

I remember seeing the first circuit some time back, but only stumbled on the second quite recently.

Was the pre war battery biasing method similar to circuit 1, or was the battery located under the cathode?
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Old 3rd April 2010, 05:57 AM   #9
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Quote:
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Was the pre war battery biasing method similar to circuit 1, or was the battery located under the cathode?
Circuit 1
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Old 3rd April 2010, 01:15 PM   #10
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Hi,

Quote:
Originally Posted by mach1 View Post
I recently came accross a novel (I think !) way of battery biasing a grounded cathode stage which I believe is attributable to Thorsten.
Neither approach is directly attributable to me.

The one used in the Toccata is from Arthur Loesch.

The second originally derived, if I remember correctly, from discussions on the Joe List where some of us recoiled in horror from the application of "battery bias" by putting nicad cells into tubes cathodes (I still think the results are poor and it is a pretty bad idea and yes, I have tried, it is nearly as bad as using LED's or Chip regulators in the cathodes to bias a tube).

The discussions resulted in the second scheme and I have been quite fond of it ever since. But I do not think I claim being the originator. This would have been in the late 90's. It is also used in the Artemis Labs Phono Stage.

I have since come up with a scheme that approximates the results, but does not rely on batteries and allows servo-adjustment of the Bias, but it is a little complex to implement and really only sensible for commercial gear.

For DIY a straight Battery is usually quite acceptable and of minimal complexity. I'd like to close by quoting "Peter Pan" from Troel Gravensen's Website:

"(This is) - not very common because people believe if it is in series with the grid; it is “in the signal path” and if it is in series with the cathode it is not “in the signal path”. So they stick a big, bad, nonlinear rechargeable Nicad Battery in the cathode, where it is exposed to a lot of varying current so this non-linearity can be injected into the input voltage loop (grid to “ground”) and amplified and they are pleased as punch with themselves for having eliminated another evil capacitor ;-)."

Ciao T
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