Is 5mA current really too low in a pre-amp??
I have currently a resistor loaded stage (20K anode resistor, 120v plate, 3.5v bias, on a EL84 triode connection)..
is this too low to drive a SS amplifier or tube amp??
also, would changing the 20K resistor to a choke load improve things??
finally, what value of choke should I use for a EL84 connected in triode mode???
there is no cathode follower on the output.
Thanks!!!
I have currently a resistor loaded stage (20K anode resistor, 120v plate, 3.5v bias, on a EL84 triode connection)..
is this too low to drive a SS amplifier or tube amp??
also, would changing the 20K resistor to a choke load improve things??
finally, what value of choke should I use for a EL84 connected in triode mode???
there is no cathode follower on the output.
Thanks!!!
Errrr, so a SET amp running a 2A3 circa 800 ohms Ri into a 2.5kohm load is utterly useless? I don't see the connection.
Now, at 5mA, yes it most certainly is.
Nice thing about small signals though, you can get away with nasty hookups because it's so small, it encounters only small amounts of nonlinearity. You can easily drive 600 ohm lines from a... 6DJ8 (huh, now that's odd, you never see that guy as a line driver), plate loaded. You might only get 5 or 10V, but it's there. I personally drive 32 ohm headphones with 12AU7 CF's at 5mA or so, it gets the job done but that's about it (only a few mW, but thus it shall remain as the PSU can't spare any more bias current).
Tim
Now, at 5mA, yes it most certainly is.
Nice thing about small signals though, you can get away with nasty hookups because it's so small, it encounters only small amounts of nonlinearity. You can easily drive 600 ohm lines from a... 6DJ8 (huh, now that's odd, you never see that guy as a line driver), plate loaded. You might only get 5 or 10V, but it's there. I personally drive 32 ohm headphones with 12AU7 CF's at 5mA or so, it gets the job done but that's about it (only a few mW, but thus it shall remain as the PSU can't spare any more bias current).
Tim
Tim, I suppose it depends on what you think is an acceptable level of distortion. Just curious, since I don't have triode-connected EL84 curves to hand- what's the change in rp when going from 19 to 21 ma?
As a signal processing device, possibly not. As a neutral amplifier, yes. But my bigotry in that regard is well-known.
Errrr, so a SET amp running a 2A3 circa 800 ohms Ri into a 2.5kohm load is utterly useless?
As a signal processing device, possibly not. As a neutral amplifier, yes. But my bigotry in that regard is well-known.
hmmm....
well funny thing...
if you look at the curves and specs....
triode EL84 looks very similar to ECC99...
and have similar "sound"
running at 120v 5mA 3.5v bias.. the triode EL84 has a very natural sound to it.. very good bass.
and this is with a 18K plate load with NO CF... driving a 80K input impedance of a tube amp..
which btw, doesn't have a very good gain and needs about 4v or so for max output.
So if for "regular" amps SS or tube.. with the 1v sensitivity I think that 5mA should be ok.
question is now:
should I put an active load on the EL84 or choke load it with a 200H choke???
thoughts?
well funny thing...
if you look at the curves and specs....
triode EL84 looks very similar to ECC99...
and have similar "sound"
running at 120v 5mA 3.5v bias.. the triode EL84 has a very natural sound to it.. very good bass.
and this is with a 18K plate load with NO CF... driving a 80K input impedance of a tube amp..
which btw, doesn't have a very good gain and needs about 4v or so for max output.
So if for "regular" amps SS or tube.. with the 1v sensitivity I think that 5mA should be ok.
question is now:
should I put an active load on the EL84 or choke load it with a 200H choke???
thoughts?
how about this:
start at 10mA, 120v plate, 4v bias
isn't 10mA plenty?????
adjust upward as needed.
problem is that my power supply is limited to output voltage... and I am going to shunt regulate it at 150v
(the 30v drop or so is for bias and drop across plate choke)..
actually see:
http://www.diyparadise.com/variation.html
which is interesting reading.
start at 10mA, 120v plate, 4v bias
isn't 10mA plenty?????
adjust upward as needed.
problem is that my power supply is limited to output voltage... and I am going to shunt regulate it at 150v
(the 30v drop or so is for bias and drop across plate choke)..
actually see:
http://www.diyparadise.com/variation.html
which is interesting reading.
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