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Old 16th July 2004, 01:59 PM   #1
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Default An Ultra -linear question

Hi all,

I have a serious problem with the concept
of ultralinear characteristic curves.

Suppose I have to find the static working point
of an Ultralinear connected SE amplifier.

I'll simly use the triode-connected plate curves since
in static condition there is no difference between
plate voltage and G2 voltage (a part from the different
due to the DC loss in that part of the trafo).

Well, but in dynamic conditions the voltage at
g2 is a definite fraction (e.g. 40%) of that
at the anode so the behaviour of the tube is
very different and the triode curves become useless.

However, I always read that the Ultralinear curves
are traced by applying, in a slow variable way with
two different generators, two different voltage to
g2 and the anode respectively, being one 0.4 time
the other. but this is very different from the real
static case of trasformer loading where the
static voltages, a part from the fall in the primary,
are equal.

So, it appear that the ultralinear curves refer to
the dynamic case. Certainly, if one uses the UL curves
to find tha static point, he will go in troubles and
obtain wrong results.

It seem , may be, that we need a different
dynamic plot for every static work point.
But it is impossible.

I am very confused.

Can somebody help me ?

thak you in advance

Federico Scarpa
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Old 20th July 2004, 03:54 PM   #2
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Hi,

Also your opinions on the subject are welcome.

Federico
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Old 21st July 2004, 09:40 AM   #3
316a is offline 316a  England
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Default UL

Quote:
Originally posted by fscarpa58
Hi,

Also your opinions on the subject are welcome.

Federico
Hello ,
I have also been pondering on the same subject as I'm about to press a quad of EL38 into UL service . The EL38 datasheet only shows pentode curves and this type does not seem to be used often for audio so I have been using comparisons of other similar valves such as the 807 and EL34 . On the Audiomatica website there are characteristic curves for pentode , UL and triode for the EL34 and 807 , may be worth a look


http://www.mclink.it/com/audiomatica/tubes/

cheers

316a
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Old 21st July 2004, 04:53 PM   #4
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Hi 316a, thank you

I know those curves but I really
do not understand static versus
dynamic description of UL connected tubes.

It seems impossible to me to
represent both static and dynamic UL behavior
with the same curves.

I'll continue to scan the web.

bye

Federico
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Old 29th July 2004, 12:12 PM   #5
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I don't find anything on the subject
clearly explaining UL plate curves.

any idea?


Federico
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Old 29th July 2004, 12:28 PM   #6
SY is offline SY  United States
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I guess I'm confused by the confusion!

The static points need to be determined by static curves. Analysis of the dynamic operation requires dynamic curves. Remember, in the case of UL, the voltages are being applied via a transformer by definition. So they are different in that sense than pentodes or triodes, where there's really no difference between the AC and DC voltages.

As a side note, EL38s work very, very well with a 6600 ohm p-p, 43% UL taps, and about 490V on the plate. I got 45 watts out of this configuration.
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