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Old 16th April 2010, 07:32 PM   #1
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Default Most linear triode-strapped pentode

Have done quite a lot of loadlines of popular pentodes for triode-strapping. Im not impressed.

Typical tubes are EL34 and 6L6, have also checked E130L and 807/1625(close to 6L6). Probably they would do in PP but as SE they dont impress me much.

The reason I ask is that I want a tube with enough linearity to be on par with 2A3 but with higher senstivity.

Any suggestions?
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Old 16th April 2010, 07:58 PM   #2
bigwill is offline bigwill  United Kingdom
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A pure pentode with plate to grid feedback

Running a pentode in triode mode is like sticking a towel in the intake of an engine!

Last edited by bigwill; 16th April 2010 at 08:00 PM.
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Old 16th April 2010, 08:44 PM   #3
DougL is offline DougL  United States
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How about a 6V6 trioded?
IIRC, Mu of 15.

Doug
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Old 16th April 2010, 09:05 PM   #4
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Try 307A, great linearity, but not so sensitive ...
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Old 16th April 2010, 09:39 PM   #5
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6p15p

6p1p

12l6gt, 25l6gt, 50l6gt

Quote:
Originally Posted by bigwill View Post
A pure pentode with plate to grid feedback

Running a pentode in triode mode is like sticking a towel in the intake of an engine!
Right. But the question was exactly about best running engine with a towel in the intake.
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Old 16th April 2010, 10:01 PM   #6
rdf is offline rdf  Canada
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Do tetrodes count? 6e6p-dr, 6e5p
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Old 16th April 2010, 10:09 PM   #7
Gordy is offline Gordy  United Kingdom
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7788 for linearity (but not 2A3 levels of power!)
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Old 16th April 2010, 10:29 PM   #8
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The short reply is that triodes are not linier, none of them. And there is no such thing as a load line. That is why we like triodes.
That line we draw on the graph paper assumes that the load is purely resistive. Plus that directly heated 2A3 is not as linier as we think. The plate curves on the 2A3 data sheet resemble the shape of the French curve laid on the page in 1943 more that performance of that NOS tube in hand.
Turn up the voltage, turn up the current, never mind the maximum rating of the tube until the plate glows red and the smoke comes out. Turn the next one down 10%. That is how to maximize the linearity.
Pentodes with feedback or triode strapped start to behave like triodes. They are not linier either. That is why we like them too.
Since this for fun trace the plate curves for that 2A3 as installed in your preferred amplifier circuit and you will not recognize it.
Try an 837 they are fun.
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Old 16th April 2010, 11:59 PM   #9
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I 2nd the 6V6 family motion. Look at the curves (page 8). The highly revered 6SN7 doesn't do better.

Inexpensive NOS is available. Buy 14C5s. NOS 12V6s still carry "rational" price tags. Want miniature types? Use 6AQ5, 12AQ5, 12AB5, and 6005. Want current production? New Sensor's Saratov, Russia, plant makes 2 nice varieties: the EH and the "reissue" TungSol.
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Old 17th April 2010, 12:51 AM   #10
jlsem is offline jlsem  United States
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D.T.N Williamson wrote that triode-connected KT-66 was nearly the same as a PX-4. So why not? A $200 tube for a $500 tube.

John
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