On Mar 29, 2:20�pm, Andre Jute wrote:
On Mar 29, 3:34�pm, Patrick Turner wrote:
Its a little known fact that one may take advantage of the UL
connection even when you don't like to.
Most ppl think the UL connection for EL34 always means 43% screen
taps.
This % was always regarded as optimal because triode like THD is
achieved and Rout reduced to give Rout = RL. But this was mainly for
class AB PP amps.
With pure class A1 PP amps or SE class A1 amps there is no reason why
ppl should not use UL taps at 75% of the P turns.
One might say well the triode connection is the best but you'll only
get about 6W from an EL34 in triode. The power output is rarely more
than 27% of power input because the Ea minimum swing is restricted by
the onset of grid current. But when you look at the load lines you can
see that one could swing a bit further if you had the tube in pentode
and get 9W from 24W of idle power.
Well, To get the swing you need, try screen taps up to 75%.
The Ra will then be about 2k which is not much above triode Ra of
1,250 ohms.
And RL can be say about 5k, so the DF is still OK, and linearity
virtually equal to triodes.
I have tried this trick in conjunction with CFB windings where the CFB
= 12.5% and UL taps are at 62.5% of the total P turns. If the OPT has
5K:5 ohm ratio, you get Rout = 1.1 ohm.
Overall gain is then like a 300B, about 4.5, Va-k divided by Vg-0V.
About 48Vrms to the grid is needed for clipping.
I get 8.5W with Ea = 350V, Ia + Ig2 = Ik = 66mA. Distortion is
virtually all 2H until near clipping.
Patrick Turner.
Clever, this, Patrick, for those who can wind their own iron. Those of
us who have buy our iron out of a catalogue have to be satisfied with
half your power. From
�http://www.audio-talk.co.uk/fiultra/...0ON%20AMPS.htm
�we have this simple SE EL34 integrated linestage built with only
three valves (envelopes, actually, as there are in total four valves)
to drive an efficient speakers (also shown at the above site):
�http://www.audio-talk.co.uk/fiultra/...L34-SEntry.jpg
More power to your arm, pal.
Andre Jute
Visit Jute on Amps at
�http://www.audio-talk.co.uk/fiultra/
"wonderfully well written and reasoned information for the tube audio
constructor"
John Broskie TubeCAD & GlassWare
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wisdom"
Stuart Perry Hi-Fi News & Record Review- Hide quoted text -
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Hi RATs!
Yes, trying to make it loud using the amplifier is just another way to
waste as much time and money as is available
Power output is measured using a steady signal, either Sin wave or
white noise. A constant signal allows accurate measurement.
Music is, at least in the olden times, was, not a constant signal.
This is where the two major politcal parties of the audio arena
diverge. Do we want accurate information or beautiful Music. Both
sides assume they know the truth. We will never know the truth. We are
human, not smart
My EL34 amp was UL, factory. It is now triode, with a diode and an R
between Plate and Screen. The Z of the OPT is now much greater than
optimal for max power output. It does sound really good
And the classic EL34/6CA7 has been replaced by 6BQ6-GTB, further
reducing power output. Oh, the horror 8*P
It does sound really, really good.
None of us knows everything, but, some of us just do whatever sounds
"nice".
Life ain't a Force March for everyone, some of us Samba.
Ole!
Happy Ears!
Al