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I mean do they sonicaly diminish at some point before they blow? Does the sound degrade at some point in its life span?
I know they are like transistors in so much as they have a YES/NO function. But like some resistors and caps do they loose their physical function?
charles
Follow Ups:
I'm not a techie, mind. I use 7189s in my rebuilt LEAK St20s.
With 7189 amps the BEST value and good sound option is the current production EL84M.
I keep my pre-amp on most of the time. Allen Wright used to recommend this idea. Mine used to be an FVP built* by Allen in its QUAD 22 box, but it has now had three rebuilds since.
I do not 'believe in' valve rectifiers for sound. Some current 5AR4 / GZ34s are I'm told a lot better than what was available when we did the rebuild. Reliability and cost were real issues.
Maximum power and tight deep bass via max. storage was / is my aim, but if you want your VR to last and last - put in Eli's series SS Rectifier mod as well. Use Schottkys. This might allow you to add a choke if there wasn't / isn't one, and perhaps increase the storage in the PSU.
My start-up hit is delayed by one of those special slow-start resistors on the mains primary. This delays every secondary voltage. I could perhaps put another one on the B+ secondary as well, but have not had any support for that idea around here. Eli? et al?!
If it uses the same driver tubes as ST70s (7199?) there is an alternative that is abundant and reliable but requires a re-wire of the sockets (?). It may be that they would benefit from a BP or FET CCS, like my twin-triode LTP 6CG7s.
Further thoughts high-GM low-gain tubes as drivers or gain-stages are a good idea. You will need far less NFB and still have lower TD and Noise. Yes it won't sound quite like it did, but it will sound better. The OPTs will still be the same.
* I was almost gifted a set of QUAD II/22 gear and a mono AM / FM tuner and swapped them to Allen for an FVP in the 22 box with a separate PSU. The only remaining bits are the boxes!!
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Friend of mine had a Cary 300B integrated, never turned it off for 7 years. Brought in for repairs, since a resistor blew, the tubes, 300B's and 6sn7's all tested as new.
Early 90's production of Chinese and Russian tubes gave tubes a bad name. Chinese tube used to literally blow up, now they simply die,as will the Russian stuff.
American and European NOS stuff were actully as tough as nails, in my experience. Turn off and on, no problem: overload their rated specs, and very little issues.
Yeah modern Russian and Chinese stuff have gotten considerably better, no question. But I really like my NOS stuff
Of the 8 EL84Ms I put in the St20s w in the 1990s we have replaced one. And that was early on.
The NoS 6DJ8s and 6CG7s made here are still fine.
Q'n- If you had a CCS FET on LTP drivers would you bother with adding a balance pot for the PP OP stages? Each tube has its own cathode R.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
I tried swapping out my old original 7189 output tubes for a new pair. It was like a vitamin B-12 shot!
When I originally got the stereo I liked the original tubes over the new ones I bought. Over MANY MANY hours I started to notice on channel loosing volume, dynamics sagging, bass getting rather muddy and the treble loosing focus, etc, etc, etc.... Basically it was sounding tired!
Popped in the new output tubes and every thing was back to normal.
However I tried it with the smaller signal tubes and found NO differences.
So now what about rectifier tubes?????
charles
Regarding small signal tubes...
I'm of two minds. Manufacturers like Audio Research tell you that tubes like the 6922 are good for only about 5000 hours. Turn off the component when not in use. With a new preamp in the main system, I adhere to their recommendation.
Just for grins, I've experimented with doing the opposite. For years, I ran a Manley tube DAC that used 12AU7s 24x7 and couldn't tell any difference even when I changed them once a year just because after nearly 9000 hours. I replaced that unit with an ARC SP9 MKIII and similarly have left it on 24x7 since last summer using 7308 tubes. I'm gonna run them until I can tell a difference or they die! I have four spare 7308s to use afterwards, but I'm finding that continuous use is not necessarily such a bad thing - again with small signal tubes.
Hey, Stat:
Does the SP9 utilize a stand-by mode, or are they fully energized all the time? Just like ARC reccos, CAT says to turn off my SL1 when not in use and it removes power completely when shut down. I had a Counterpoint preamp that always kept the filaments warm and had to be unplugged from the wall to completely shut it down. Mike Elliott the designer of that pre felt that the thermal cycles of going from stone cold to hot was more damaging to tubes than leaving the filaments energized. My Acoustat servos keep the filaments warm all the time too, but from what I understand Jim Strickland did that mainly because the humidity in Florida necessitated keeping the amps warm to drive off the moisture. So, I've had amps/preamps that keep things on and I've had them that keep things off, and I can't say I've really seen any differences in how long tubes last. Would be interested to hear what you think after you've finished your testing.
The SP9 offers a mute circuit, but I'm pretty sure that only disconnects the output. I think it remains fully energized. While not tubes, I also keep the Stasis 3 on at all times.
I used the Acoutat X with servo amps in the late 70s. I remember the relay that would click and wake up the amp for full operation.
The 7308s in the preamp were installed 9/12 although I wasn't running them 24/7 before I moved the preamp to the garage. Indeed, they are longer lasting versions of the 6922 with an expected life of around 10,000 hours. I see no reason why I can't easily double that.
Yeah, it was a neat idea to have the servos wake up and go to full power when they detect signal on the input, but it didn't do much for the sound of the amps. All that wake up circuitry has been removed from mine. The filaments stay warm all the time, and then there's a toggle switch that brings filament voltage fully up and kicks the relay to turn on all the high-voltage stuff when you want to listen.
I thought both the 7308 and the 6922 were 10,000 hour rated tubes. The differences, if I remember correctly, were that the sections in the 7308 were guaranteed matched to with 10% from the factory, and they can take more voltage on the plates than the 6922. Either way, that's a looong time to run a tube.
I was lucky enough to have scooped up a mint Sencore MU150 several years ago, and after I've had a tube in service for over a year usually, I'll pull it and run gain test on it while hitting the "life-test". Any tube that shows significant drop in reading gets the hook. On that basis, most tubes seem to have a serviceable life for me in the 2-3 year range. Keep us posted how the test comes out.
I thought both the 7308 and the 6922 were 10,000 hour rated tubes. The differences, if I remember correctly, were that the sections in the 7308 were guaranteed matched to with 10% from the factory, and they can take more voltage on the plates than the 6922.
You're right. I must have been thinking about the difference between the original 6DJ8 and the 6922. Having said that, ARC used to recommend changing after 5000 hrs on their old web site.
I'm curious. Because I have a fully rebuilt Sherwood with original tubes circa 1958. The preamp tubes are RCA blackplates, outputs Phillips 7189's. And the driver tubes are of course the pain in the @ss 7199.
I don't want to start rolling tubes. Being my farting around days are over. I'm in listening mode now. But I do have a full set I bought from Jim McShane.
charles
I've generally noticed diminished volume AND bass, as a tube starts to slowly expire.
Steve
If you talk to vintage tube radio guys, even those tubes with low emission, as long as they are not glassy, they still function ok for long time on radio. A friend of mine, he plays guitar, he like to use those "tire" 6l6, 5881, on his practice amp.
Luckily, they are easy to remove & replace.
They will gradually use themselves up, but if there are no other problems in the gear that can take a long time; even thousands of hours. It is very seldom the tubes that are causing the trouble with gear that is not working properly.
Edits: 04/14/15
"like some resistors and caps do they [tubes] loose their physical function?"
Sure, that's one of the reasons we don't use them anymore. They get gassy, their cathode emission craps out, the grids start rattling and become microphonic and eventually the heater burns out. Or they short from a sliver of one of the elements touching another and their pin-socket contacts are always problems from the thermal excursions. By and large tubes suck compared with solid state for reliability and consistency.
But sometimes they seem to last forever and it's apparently a combination of happening to be produced well along with an application they like. They achieve the most service-hours in low stress applications where they are on constantly.
Solid state and passives are generally orders of magnitude more reliable.
Rick
And many orders of magnitude less enjoyable to listen to .....
In my life with tubes so far no tube got tired but a coupled have died suddenly and scarily. I am not fond of tube arc light shows!
Steve
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