Most linear triode-strapped pentode

revintage · 16th April 2010, 07:32 PM

Have done quite a lot of loadlines of popular pentodes for triode-strapping. I´m 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 don´t 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?

bigwill · 08:00 PM

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!

DougL · 16th April 2010, 08:44 PM

How about a 6V6 trioded?
IIRC, Mu of 15.

Doug

radiostar · 16th April 2010, 09:05 PM

Try 307A, great linearity, but not so sensitive ...

Wavebourn · 16th April 2010, 09:39 PM

6p15p

6p1p

12l6gt, 25l6gt, 50l6gt

Quote:

Originally Posted by bigwill

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.

rdf · 16th April 2010, 10:01 PM

Do tetrodes count? 6e6p-dr, 6e5p

Gordy · 16th April 2010, 10:09 PM

7788 for linearity (but not 2A3 levels of power!)

DualTriode · 16th April 2010, 10:29 PM

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.

Eli Duttman · 16th April 2010, 11:59 PM

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.

jlsem · 17th April 2010, 12:51 AM

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

16th April 2010, 07:32 PM	#1
revintage diyAudio Member Join Date: May 2007 Location: Eskilstuna, Sweden	Most linear triode-strapped pentode Have done quite a lot of loadlines of popular pentodes for triode-strapping. I´m 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 don´t 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? __________________ Brgds Lars

16th April 2010, 07:58 PM	#2
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	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.

16th April 2010, 08:44 PM	#3
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 25	How about a 6V6 trioded? IIRC, Mu of 15. Doug __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

16th April 2010, 09:05 PM	#4
radiostar diyAudio Member Join Date: Apr 2009	Try 307A, great linearity, but not so sensitive ... __________________ tubes.rs facebook.com/tubes.rs

16th April 2010, 10:01 PM	#6
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	Do tetrodes count? 6e6p-dr, 6e5p __________________ Ears aren't microphones.

16th April 2010, 10:09 PM	#7
Gordy diyAudio Member Join Date: Nov 2006	7788 for linearity (but not 2A3 levels of power!)

16th April 2010, 10:29 PM	#8
DualTriode diyAudio Member Join Date: Aug 2009 Location: Sacramento	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.

16th April 2010, 11:59 PM	#9
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	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. __________________ Eli D.

17th April 2010, 12:51 AM	#10
jlsem diyAudio Member Join Date: Jun 2003 Location: Dallas,TX	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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