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Best sounding power pentode/tetrode in triode for SE?

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Posted on October 3, 2020 at 02:14:02
andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000
 For the last 12 years I've been using either SE 300b outputs or PSE 4P1L outputs (a pair). This sets a very high level of sound quality. I'm wondering if there's an indirectly heated tube that can approach this level of sound. I'm only interested in triode operation here. Looking for 15W to 18W dissipation, something like 60mA and 250v-300v a-k as a minimum, but that would be enough.

Contenders in PSE for a pair of tubes could be 6V6, EL84 or a lot of older tubes like KT61 and its variants.

Contenders in SE are EL34, 6L6-GC, 5881, 6550, KT88, GU50, 6CB5A etc. From what I read the EL34 has the best triode curves, though others like 6CB5A and GU50 have fans.

It may be the case that none of these can match a 300b or PSE 4P1L. Just want to know what comes close.

 

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RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 3, 2020 at 04:32:26
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 Triode wired 6V6 family tubes are very nice. A remark not original to me is that in this power range, you have to use #45 DHTs to do better.

I can tell you from personal experience (DECWARE SE84) that triode wiring the Russian 6Π15Π (6p15p) is quite satisfactory. The independent connection for g3 allows experimentation with its attachment. Connection of g3 to either the cathode or the plate can be tried. As is frequently the case with Russian types, specimens with the EB (ev) suffix tend to be superior.


Eli D.

 

Is GU50 a contender?, posted on October 3, 2020 at 06:45:25
andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000
 I see Anatolyi makes amps with the GU50. On the other hand, for low power he prefers the 4P1L.

I'm unfamiliar with the GU50. It turns up in some Chinese amps. Should this be on my radar as regards sound quality in triode?

 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 3, 2020 at 08:22:16
FlaCharlie
Audiophile

Posts: 940
Location: Gville, FL
Joined: June 1, 2003
 Have you tried 12P17L? I was under the impression that it is essentially an indirectly heated version of the 4P1L. Is that correct?

How about 6A5G? It's an indirectly heated 2A3 / 6A3 / 6B4G. I built a SET with them a while back using 27 input.




 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 3, 2020 at 16:47:38
dhsettim
Audiophile

Posts: 181
Joined: January 10, 2002
 EL509/519 in Enhanced Triode Mode connection
or
EL504 in triode connection

 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 4, 2020 at 06:21:08
PakProtector
Audiophile

Posts: 12366
Joined: May 14, 2002
 Have to suggest that the rest of the amp design might just play a fair part of the 'goodness'. That will give you some fits separating wheat from chaff.

IME, the 6CB5A, when rigged as pentode, and bent into very linear and low output Z triode curves by local FB sounds very good indeed.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 4, 2020 at 10:56:58
Tre'
Industry Professional

Posts: 17306
Location: So. Cal.
Joined: February 9, 2002
 I read that the plate resistance of a pentode in Enhanced Triode Mode is about the same as if connected as a pentode.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 4, 2020 at 20:19:37
hahax@verizon.net
Audiophile

Posts: 4310
Location: New Jersey
Joined: March 22, 2006
 It works. A couple of decades ago Melos built SE monoblocks with I think 2 output tubes and got 70 watts. But the way to make a triode with these tubes is to drive the screen which takes current. And in order to get maximum power from them you will probably need to drive them with a solid state device. Melos used a MOSFET cathode follower after the driver stage.

 

There's a reason for that..,, posted on October 4, 2020 at 20:58:41
Steve O
Audiophile

Posts: 12383
Location: SE MI
Joined: September 6, 2001
 ...Although the term is "enhanced triode mode", the actual operating mode is still pentode. Attached plot is for 6CL6 pentode where g1 is held constant (at 0 V) while g2 is varied as with enhanced triode mode. The set of curves is clearly characteristic of pentode mode of operation although spacing of curves is maybe a bit more linear than conventional constant g2 V variable g1 V.

 

Thanks nt, posted on October 5, 2020 at 11:10:27
Tre'
Industry Professional

Posts: 17306
Location: So. Cal.
Joined: February 9, 2002
 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 6, 2020 at 01:52:39
Boli46
Audiophile

Posts: 91
Location: Uppsala
Joined: March 6, 2015
 The Siemens F2a connected in triode is a very good tube. It's not cheap, but it's a 10 000 hour tube, unusual for an output tube to say the least, and will last a very long time. It's also easy to drive. If you look at the datasheets, don't be fooled by the high distorsion figures. For some reason, distorsion was measured with a 1,5 KOhm load.

The 6CB5A has been mentioned. I use it in a push pull amp to great effect, but so far not in SE. It has the advantage of being very cheap. Last time I bought some they were only USD5/ea. This tube is Thomas Mayers favourite IDHT output. Lot's of info on his Vinylsavor blog.

 

RE: 6CB5A - good power in triode mode, posted on October 6, 2020 at 03:09:40
deathtube 667
 6CB5A. SE triode connected finals @ 23W anode in 2 stage cap coupled circuits.

I recall the tube was sort of hard to drive and needed a preamp in front of it.

Also tried low power SE parallel feed finals.

Only NOS tubes will be available, if that matters. The top cap can be annoying as well.

As commented below, the associated circuitry with have some influence on final outcomes.


DT 667

 

RE: 6CB5A - good power in triode mode, posted on October 6, 2020 at 08:50:07
PakProtector
Audiophile

Posts: 12366
Joined: May 14, 2002
 Sounds best as pentode, g2 voltage matched to the Class A load, and driven by an E-Linear rigged EL84. E-Linear connection established by 50% taps in the primary coil. 5k a-a, or 2.5k SE. B+ or 270 and idling at 100 mA...and the plate showed no color until 115 mA idle. The LC ps filter and 866's did not drop the voltage appreciably.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

How about PT 15 valve, posted on October 6, 2020 at 09:16:49
bouncy ball
Audiophile

Posts: 1221
Location: British Columbia
Joined: July 26, 2003
 I had tried it years ago. The sound is comparable to KT66 triode mode.
Some British even claimed the sound was similar to PX25.

 

RE: How about PT 15 valve, posted on October 7, 2020 at 07:44:09
andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000
 Fascinating valve, but requires a high primary impedance for the OPT since Rp is 2.6K in triode.

There's the PT5 but that looks very scarce - can't see any meaningful data. Are there triode curves for PT15?

 

sorry, i don't have that informaion(nt), posted on October 8, 2020 at 06:30:17
bouncy ball
Audiophile

Posts: 1221
Location: British Columbia
Joined: July 26, 2003
 .

 

RE: sorry, i don't have that informaion(nt), posted on October 10, 2020 at 11:49:14
kobasa@xs4all.nl
 Love the gm70 and even more the SV572-10 and SV811-10

 

RE: Best sounding power pentode/tetrode in triode for SE?, posted on October 27, 2020 at 10:11:25
Cleantimestream
Audiophile

Posts: 7551
Location: Kentucky
Joined: June 30, 2005
 "From what I read the EL34 has the best triode curves"

No Sir, {so far as I know} that belongs to a 6V6 and by extension, a 6AQ5.

Am not talking about exotic... like an 8608.
The Mind has No Firewall~ U.S. Army War College.

 

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