Pentode vs. Ultra Linear

Posted by Freo-1 (A) on April 19, 2015 at 07:30:21

The last couple of amp projects I have had built use pentode as opposed to ultra linear. I have to say that I find pentode sounds (subjectively) better than ultra linear amps I have owned (which includes the mighty HK-Citation II).

I've been pondering WHY this seems to be, when I cam across this thread about Stu Hegman talking to Bob Carver. This passage is very telling:

" And he didn't. The Citation V was pure pentode, as was the subsequent Lafayette 550 and everything else he designed from then on. I asked how come. He explained that when the plate pulls the top of the output transformer winding towards ground, the ultra-linear tap pushes the screen grid so low that it renders the tube unable to drive difficult loads. In addition, he pointed out that the normal idle potential on the screen grid regularly exceeded a safe voltage, often causing output tubes to blow up. The tube manufacturers hated it, but had to go along or lose market share, and so changed the specification for screen voltage in order to allow ultra-linear output stages. I wonder if they changed the tube design, or just changed the screen voltage specification."

One of the reasons I gave up on the HK Citation II was the dodgy longevity of current 6550/KT88 tubes. I ran out of NOS GE 6550A's. There are some good sounding ones made today, but too many issues with how long the tube can go before something bad happens. They are not cheap, either.

The last two DIY amps I have are pentode output. One uses the 1625 tube in a quad mono setup at 110 watts, and a pair of 6883B tubes at 90 watts. The output tubes are NOS, readily available, very reasonably priced, and RELIABLE. They both sound outstanding. The dynamics, low level detail, and quietness of the amps are remarkable.

So, anyone else work this out yet?

" Don't look back. Something may be gaining on you"

Satchel Paige

http://www.audioasylum.com/audio/tubes/messages/20/209631.ht (Open in New Window)

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Topic - Pentode vs. Ultra Linear - Freo-1 07:30:21 04/19/15 (34)

some reference materials and the "UL patents" - mqracing 23:52:45 04/19/15 (1)

Good stuff - thanks! (nt) - Triode_Kingdom 05:36:27 04/20/15 (0)

THere is another school of thought as well. - Michael Samra 19:10:10 04/19/15 (0)

Pentodes with regulated screens - garymuffley 16:00:10 04/19/15 (0)

RE: Pentode vs. Ultra Linear - lugnut1 14:11:18 04/19/15 (0)

RE: Pentode vs. Ultra Linear - Stuben 14:11:13 04/19/15 (0)

RE: Pentode vs. Ultra Linear - Triode_Kingdom 09:14:18 04/19/15 (0)

RE: Pentode vs. Ultra Linear - banpuku 08:59:47 04/19/15 (1)

RE: Pentode vs. Ultra Linear - Freo-1 13:34:09 04/19/15 (0)

RE: Pentode vs. Ultra Linear - Eli Duttman 08:22:25 04/19/15 (24)

RE: Pentode vs. Ultra Linear - krankkall 09:39:49 04/19/15 (23)

RE: Pentode vs. Ultra Linear - Eli Duttman 10:58:26 04/19/15 (3)

RE: Pentode vs. Ultra Linear - Triode_Kingdom 12:48:32 04/19/15 (2)

RE: Pentode vs. Ultra Linear - Eli Duttman 14:24:22 04/19/15 (1)

Yes, it does add some cost - Triode_Kingdom 16:02:28 04/19/15 (0)

RE: Pentode vs. Ultra Linear - Freo-1 10:54:06 04/19/15 (18)

RE: Pentode vs. Ultra Linear - PakProtector 18:02:05 04/19/15 (15)

I think one needs to take that quote with a big grain of salt... - Steve O 20:45:21 04/19/15 (14)

sounds like the Carver that we know and love - richardl 14:03:02 04/20/15 (0)

You mean these? - Michael Samra 02:47:05 04/20/15 (2)

RE: You mean these? - autospecialty 17:55:17 10/28/18 (0)

That's it! (nt) - Steve O 05:19:13 04/20/15 (0)

RE: I think one needs to take that quote with a big grain of salt... - unclestu 21:17:17 04/19/15 (9)

What was the timeline for this work? - Triode_Kingdom 05:45:44 04/20/15 (2)

Late 80s-early 90s... - Steve O 06:34:39 04/20/15 (1)

RE: Late 80s-early 90s... - Triode_Kingdom 07:43:02 04/20/15 (0)

RE: I think one needs to take that quote with a big grain of salt... - mqracing 00:53:55 04/20/15 (3)

PS never worked on a Mk VI - unclestu 02:58:08 04/20/15 (0)

Whoa !!! - unclestu 02:52:59 04/20/15 (1)

and.... - PakProtector 10:37:20 04/21/15 (0)

RE: I think one needs to take that quote with a big grain of salt... - Steve O 21:56:57 04/19/15 (1)

LOL!! - unclestu 22:41:29 04/19/15 (0)

RE: Pentode vs. Ultra Linear - Triode_Kingdom 13:57:36 04/19/15 (1)

6146/6883B is very linear... - Freo-1 14:34:13 04/19/15 (0)

Pentode vs. Ultra Linear

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