Longevity of output tubes in triode vs pentode

john dozier · 13th March 2011, 09:48 PM

I have amps that operate in both triode and pentode modes(switchable) The output tubes are EL-34s. Is there any difference in longevity between triode and pentode operation? Thanks

DF96 · 13th March 2011, 10:17 PM

Given the same current and hence dissipation I would guess no difference.

bigwill · 10:46 PM

Depending on the circuit, the screen grids might have a slightly tougher time in pentode mode because they can't swing down with the anode, which will increase the screen current during peaks. However, as long as everything is within spec it is not a difference worth worrying about at all. Pentode is more efficient so you'll be getting more use out of the valve for a given dissipation (and with carefully applied feedback distortion as low or lower than triode mode)

kevinkr · 14th March 2011, 03:48 AM

Pretty much a non-issue as far as I can tell. A number of my clients had me build ST-70 configured for bi-amplification with one channel in UL mode for the bass and the other in triode mode. Both channels operated at the same quiescent current and the tubes wore out regardless of mode at the same time.

john dozier · 14th March 2011, 11:15 AM

Thanks everyone. There were reports on another board that triode operation had an adverse effect on tube life. I am glad to know it is hogwash. Snake oil, snake oil, forever. Thanks again

13th March 2011, 09:48 PM	#1
john dozier diyAudio Member Join Date: Dec 2010 Location: columbia sc	Longevity of output tubes in triode vs pentode I have amps that operate in both triode and pentode modes(switchable) The output tubes are EL-34s. Is there any difference in longevity between triode and pentode operation? Thanks

13th March 2011, 10:41 PM	#3
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Depending on the circuit, the screen grids might have a slightly tougher time in pentode mode because they can't swing down with the anode, which will increase the screen current during peaks. However, as long as everything is within spec it is not a difference worth worrying about at all. Pentode is more efficient so you'll be getting more use out of the valve for a given dissipation (and with carefully applied feedback distortion as low or lower than triode mode) Last edited by bigwill; 13th March 2011 at 10:46 PM.

14th March 2011, 03:48 AM	#4
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Pretty much a non-issue as far as I can tell. A number of my clients had me build ST-70 configured for bi-amplification with one channel in UL mode for the bass and the other in triode mode. Both channels operated at the same quiescent current and the tubes wore out regardless of mode at the same time. __________________ www.kta-hifi.net

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Triode Pentode combo tubes	TheGimp	Tubes / Valves	35	6th October 2011 08:13 AM
Pentode to Triode Operation	Monjul	Tubes / Valves	13	21st September 2010 11:27 PM
Triode connecting a pentode?	Original Burnedfingers	Tubes / Valves	15	3rd July 2006 05:10 AM
Pentode to Triode trick.	Diy martin	Tubes / Valves	4	7th November 2005 11:00 AM
triode vs. pentode for pp output.	9am53	Tubes / Valves	1	17th March 2005 07:34 PM

13th March 2011, 10:17 PM	#2
DF96 diyAudio Member Join Date: May 2007	Given the same current and hence dissipation I would guess no difference.

14th March 2011, 11:15 AM	#5
john dozier diyAudio Member Join Date: Dec 2010 Location: columbia sc	Thanks everyone. There were reports on another board that triode operation had an adverse effect on tube life. I am glad to know it is hogwash. Snake oil, snake oil, forever. Thanks again

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read