Re: Battery bias directly to grid



bruce seifried wrote:

> In article <1129479453.815805.139670@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> "Andre Jute" <fiultra@xxxxxxxxx> wrote:
>
> > I've posted a circuit for discussion at:
> >
> > http://members.lycos.co.uk/fiultra/Discussion%20Circuits.htm
> >
> > What are the implications of this circuit?
> >
> > What, theoretically, makes it better than the standard battery bias
> > application in the cathode circuit?
> >
> > Will the batteries charge as efficiently in this position as in the
> > cathode circuit; what are the effects of the resistors topping and
> > tailing the battery set?
> >
> > What are this circuit's dangers?
> >
> > Are there alternatives that work better or are safer?
> >
> > Andre Jute
>
> I note that the circuit you're describing is quite similar to an amp
> design you have published on your website, the Type 39, Series VI "The
> Tradition":
>
> http://members.lycos.co.uk/fiultra/T39-KISS-300B-Ultrafi-crct.jpg
>
> I assume you've actually built this circuit and tried it, so you should
> know that rather then the circuit *charging* the batteries, they will
> eventually be *discharged* by the input attenuator, especially in low
> gain settings. You are also sending dc out the input jack to the
> preceding piece of gear, which, in the case of a transformered output
> circuit, will discharge the batteries at *high* gain settings.
>
> Changing the gain setting will also tend to send a transient pulse into
> your speakers.
>
> If you're going to use this topology, you'll need to bite the bullet and
> use a cap between the pot and the batteries/grid.

If the input grid appears slightly negative with respect to the bias supply,

then minute negative grid current can flow and very slowly discharge the
battery.
If the grid become a little positive, I flow is charging to the battery,
but this occurs when the tube is old and past its use by date.

But the transients you speak of don't occur any more than with any other
biasing method.

Patrick Turner.

>
>
> -bruce seifried

.

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