Fixed bias arrangements

For the three and more legged things
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Paul Barker
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#1 Fixed bias arrangements

Post by Paul Barker »

Let's put this thread in solid state as that is what it is.

You may remember an old pejudice of mine about battery cathode bias being questioned, and I went away and found a link to when I first came out about my hatred of diode bias whether led or not. Right at the beginning I learned this when it was very unpopular to say it was pants. Also battery cathode biasing I was guity of being a sheep in this respect for many years untilt hat day when at Nick's we thouight let's try resistor instead of the battery and found the improvement more than slight.

Since when my favourite has been unbypassed (when possible) resistor bias and second to that valve rectifier bias, and third bypassed resistor. I have never used an led or other non vacuum tube diode or battey in the cathode since. The faults of the above are a clear as day to my hearing in my amps on my speakers.

I never liked the way Thorsten gets attributed to methods which turn out to work well, though he never invented them or laterly discovered them. But I have had to live with the fact that a lot of the lemmings out there can't discern and just like to prostrate themselves in front of firm leadership.

But in this instance while googling about battery bias I was delighted to find a statement from Thorsten which supports what I have always said (though he said it many years after me, and not at a time when it was probably as unpopular a statement as to dis 300b's).

"Of course, next to a LED most batteries look as close to perfect as it gets on grounds of noise and linearity.

I would, based on personal experience rank LED Bias last, together with 3-Pin regulators in cathodes, in terms of subjective sound quality and last in terms of measurable linearity but second last on noise.

Fixed bias using Lithium batteries in series with the grid where the input must be ground referenced (or the active bias variant of it) and conventional fixed bias is number one. By a long stretch. All else being equal not having anything between cathode and (signal) ground beats all options of having something there." DIYAUDIO 4th April 2010.

So now that one of the sacred cows has spoken on the matter perhaps people will believe me rather than challenge eveything I say.

So now that we can move on and lean from the experiences of the last 12 years which have seen all sorts of popular but audibly poor biasing methods adopted by the masses, where are we?

Well I am still very fond of unbiased resistor for it's simplicity and it's feedback effect on the linearity of that single stage.

But my next thought goes to what to do when this can't be. For myself to add a capacitor is a failure, but to be fair it is a pretty good solution which doesn't degrade the sound very much, yet I do hear a clear shift from perfection to near perfection.

So I am left in new teritory for me of tying what has always been considered "best" by the old guard; FIXED BIAS.

Now I remember a conversation with Nick in which he suggested the use of solar panels controlled by light for various things. I did tie myself in knotts trying to figure out if the £1 shop garden lights could make me a 90v power supply for first stage where a 1mA tube is used at 45v with 45v across load resistor. But I decided that for the moment it is too much faffing around. Though for a future project it might come out.

But the thought is that inside the amp there could be a place made for a 230v halogen lamp to face a small solar panel adjusted by light dimmer to set "fixed" bias.

Or the included li battery in the garden lights may be used.

Or above but with solar panel attached exposed to elements so the li battery gets a top up.

thoughts?
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#2

Post by Paul Barker »

OK couldn't resist for £44 delivered 190v at 80mA should make a nice little 750mW to 1.75 Wat amp depending which tubes (71a, 10, 6em7, 2a3 etc)

Roughly speaking at 190v should get 1.75 watts from a 2a3 in a1 into 3k
or 1.74 watts from 10y in A2 4k5 load
would have to use the 150v for the 6em7 for 1.5 watts
790mW from 71a or 45




Here
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izzy wizzy
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#3

Post by izzy wizzy »

Well Paul, battery bias in the grid does it for me over all other methods I've tried. I wish it didn't but there it goes. Stoopid hobby.

cheers,

Stephen
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Paul Barker
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#4

Post by Paul Barker »

Thank you Stephen. That's good news for me, easy to implement, saves on B+.
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#5

Post by izzy wizzy »

I should have said, I've only done it at small signal levels. Dunno what happens outside of that.

cheers,

Stephen
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