Re: Battery bias directly to grid

I can't speak for other heads, but the inside of mine finds itself
no further forward. It would help if you were to say what you are
using as a source in your listening test.

Using the battery *instead of* the grid leak gives you a 1ohm shunt
across the lower leg of the attenuator, which is not a good test of
the principle. Perhaps you mean *in series with* the grid leak?

All methods of grid bias in the absence of DC blocking will result
in biasing the source, obviously. Here again it is not clear whether
that in itself may have degraded the sound, so again the test is
inconclusive.

A battery at the foot of the attenuator would not discharge itself
in the absence of a grid leak, and the circuit would be just as
simple as the one you have chosen. The battery could also be charged
through the signal input with the amp off, so recharging could be a
switched function of a dedicated preamp. I dare say there would be
objections to this option, and I wonder what they would be.

What I would really like to know is would it be better, leaving
aside the issue of DC blocking and recharging, to bias via the grid
or the cathode? And would a series or a shunt connection to the grid
be more appropriate?

Do batteries have the same impedance in both directions? Are they
more noisy when discharging, or charging, or in equilibrium? What
are the mechanisms of distortion and will it be less in the
high-impedance low current input or the low impedance high current
cathode circuit. Will it be less by a factor greater than the
relative gain?

I would be surprised if these issues had not already been resolved,
considering you say that the cathode connection is so common. It
seems unlikely that the obvious alternatives were not explored, or
that the merely practical charging and DC blocking issues won the
day with the "ultra fi" fetishists.

And don't forget all of your famous guru friends, who I am sure
would be happy to advise you. I would be interested to hear their
views.

cheers, Ian



"Andre Jute" <fiultra@xxxxxxxxx> wrote in message
news:1129658943.962078.103860@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Uh-uh, Bruce. What you're talking about is the battery in the
> place of
> the grid leak resistor, between grid and ground. That's a low
> impedance
> path to ground. I've tried that one with a DACT, a high precision
> Swiss
> medical switch with SMD resistors and ultrashort paths, with the
> tube
> in position to amplify the clicks if any, and the amp working into
> ultra-sensitive horns, and I heard no clicks.
>
> I republished the T39 KISS Ultrafi circuit with the batteries in
> the
> third possible position, in the cathode circuit, simply because I
> could
> hear no difference with the battery in the grid leak position, and
> the
> cathode circuit position has the very great advantage of being
> more
> failsafe than either of the other two positions, by virtue of the
> trickle charge the tubes can enjoy there.
>
> One final note on the *discussion* circuit I published (battery
> between
> wiper of attenuator and grid of signal tubes) : A "professional"
> implementation would use at least a resistor and a bypass cap in
> addition to the battery, as has been pointed out by you and
> several
> others. But I'm not interested in defending a circuit before
> professional production engineers. I'm interested in simplifying
> the
> circuit to what sounds best, regardless of expense or
> "professional
> practice", and in this case, because I am publishing the circuit
> for
> amateurs, in making it reasonably longlasting (there is a
> companion
> circuit, called the T44 "Populaire", with autobias, recommended
> for the
> newest aspirants, precisely because it is a largely self-adjusting
> circuit). Thus the return to the battery in the cathode...
>
> Thanks to all who contributed valuable insights (even if we were
> all
> talking about different circuits!). I'm removing the discussion
> circuit
> because it really doesn't add much to our wisdom; it may be a
> viable
> alternative (in that it works) but it is a decidedly less
> desirable one
> than the battery in the cathode circuit. That's the point of
> discussion
> with one's peers, to choose the best course of action from among
> possibilities.
>
> Andre Jute


.

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