tube burnout

I have owned a tube pre (Grant 100) for a few years and have been satisfied with the sound generally. My concern is that it eats up tubes. It takes six 6922's
with two of them in the mm phono and the others in the linestage. I have gone through about two dozen tubes in the last few years, and it does not matter what brand tube it is either.
This almost always happens to the phono tubes where they start out fresh, only to discover a month or two later these tubes start to get noisy. When replaced,
I get a month or two again before the noise starts up again and they must be replaced. While this is going on, the other four tubes in the linestage are not affected and play fine on any source other than vinyl.
I have tried 6922 from most manufacturers including new and NOS.
I had the pre checked and they said it was fine, just bad tubes to be replaced.
Which I did, and did, and did. All to no avail.
Still the problem persists. I can't believe that all the tubes I keep installing
are 'lemons'.

Does anyone have any suggestions?
How long do you allow your pre to warm up before you start listening? I was running through tubes (6550 & KT88) in my Prima Luna amps at an alarming rate, until I started to let the amps warm up for a half hour or so.


Makes no sense, your pre is a lemon. Whoever told you it's fine is wrong. If that was the manufacturer re: warranty demand a replacement. If it's not under warranty, ship it to Bob Backert in PA to repair it. He's a wizard. Cheers,
I'm not familiar with your pre-amp but some pre-amps drive their tubes hard any many tube brands just won't work or live long in them. I have lived with your problem (or a problem with exactly the same symptoms) for over 20 years and have went thru a lot of new and NOS tubes. An ARC SP10. I use NOS 6h23's, tested for low noise, which are very quiet and very rugged. I've been using them for 10 years and have yet to have a failure.
Changed tube vendors? Changed tube makes? New ones and used ones, and still it doesn't seem to matter as the results persist?

yep... I'd say the pre is a lemmon... despite the statements of the maker.

If it walks like a duck, and looks like a duck, and swims like a duck, it ain't a water tight chicken... it's a duck.

Sorry to hear it, but sure hope it works out for you.
Hi guys,
I allow the pre a few minutes before playing music, at low volume for the first twenty min to half an hour. This goes for the amps as well.
I am leaning towards this way of thinking also. I believe that somewhere, something is feeding the phono tubes more voltage than necessary causing them to slowly deteriorate.I am not an electronics tech though.


Yes I tried different vendors
tube makers
new ones,NOS, used
still it does'nt matter
Are you on conditioned power? If it were me; I would be looking at ac power or the pre amps' own power supply.
You might try a 7DJ8 . It's 7 volt rating makes it more robust and may withstand being pushed harder better . Also Tungsram 6922/6DJ8 type tubes are known to last longer than others of this type when pushed hard .
I second 6h23 Russian tubes.
You need to try a 6922 similiar to the ones used by Audible Illusions which require a 6922 with higher output. The ones by Russian manufacturers are more rugged. The Electro Harmonics, Sovteks, are good....6H23N-EB, 6N23, should do the trick....provided the circuit is sound...Jallen
Like the others have said, you may have a lemon.

What is the voltage coming out of the wall? If the manufacturer runs these near the edge and you have much over 120, that could be speeding things up.

it'sd been a while since I've done tech work but if your pre is self/auto biasing, perhaps the plate voltage is too high. This could happen during start up only... or continue during operation. Though not at every turn on.... which would explain the makers statement that they found nothing wrong. Intermittent issues are the worst to figure out, ...if of course, this is the thing. running too hot sure would explain the shortened life expectancy though.

Another thought is the common thread note... as both the line stage and phono stage experience the same issues, ultimately, looking at what is common to both seems in order... output stage breakdown could be asking for a greater signal magnitude and create a higher continuous voltage through the input stages. Grounds or shorts and even poor connections, or those who have broken down over time, will cause such things.

have you had to raise the vol level more so as time has passed than you did originally??

It's obvious they've missed something... give them another crack at it on their dime this go 'round.

I'd also start fresh by asking what they've determined is average tube life with this unit?

Prior to or surely thereafter a decision to fix or replace is on the horizon... or stock up on tubes!
No, only the phono stage tubes in the pre get affected
No, I have not had to raise the volume level more
It was an electronics repair shop, not the manufacturer that checked it
You will hear noise in the phono stage tubes at lower level than in line stage due to high gain. That's why some tube sellers "grade" their tubes as driver grade, line grade and phono grade (decreasing noise). IF (no idea) your pre runs the tubes hard (some are famous for that) and if the tubes are a little noisy to begin with, then its easy to see that you could go through lots of tubes. You may ease the cost burden by cycling them from the phono to the line stage when they start to get noisy and see if they can be used in that portion of the circuit.
Years ago Audio Research had a similar problem with the 6DJ8s in the SP-10 (when you tried to use a low output MC cartridge). The tubes would only last about 2 weeks. Higher output cartridges allowed you to run the tubes *a lot* longer.

If the 6DJ8/6922 is not set up right, there are a number of design parameters that can cause it to go noisy prematurely:

* the tube requires a thorough warmup without B+, so you need a time delay circuit
* its possible to 'starve' the plate, and while you get good gain, the grid will eventually get contaminated, so
* its better to run the tube hot and get less gain.

It was the experience with the SP-10 that made us realize that when we did our preamp that it would probably be a good move to avoid 6DJ8 family tubes. They are not intended for audio, so low noise and low microphonics are challenging (although they are quite linear).

Do you feel the 6dj8 family is equally bad for phono and line stage preamps or not so good for line stage and worse for phono?
My experience is that its very difficult to come up with 6DJ8/6922 tubes that do not exhibit some sort of microphonic signature, much more so than tubes that are actually designed for audio, like a 12AT7, 6SN7 or the like. It seems that 6DJ8s are far more likely to offer a signature, the louder you play the system the more you hear it.

We never considered them for our phono circuitry after a variety of experiences we had with them in the 80's, the SP-10 being among them. We did use them in our amps up until about 1990; finding tubes that didn't ring was challenging enough that we moved away from the tube after that.
Atmasphere, Thanks.
Sounds allot like either a filament or high voltage supply design flaw or defect due to a blown part. It would not be difficult to modify or repair.
Hi Guys,

Thanks for all the responses!
The last time I listened to vinyl I was plagued by the same problem. That is,on turn on I would listen to vinyl at low volume and everything was OK for the first fifteen minutes. Then, a low level distorted sound that got intrusive very quickly would appear. On FM everything sounded fine.

Today, I replaced the phono section tubes with a set from the line stage and replaced those with a known set of good ones. Upon turn on there was distortion right away on phono but not on FM.

I believe that there has to be something up in the circuit like Lamphear says.

One other thing. Phono sounded good before with a Shelter 501. Now I have a Shelter 9000 and it is a LOT better ( when the phono stage is not acting up).
I use a step up transformer to the MM section of the pre. The sound has a lot of the audiophile attributes we look for. But, how come with a cheap Kenwood tuner from the seventies the sound is more 'pleasing'?
It sounds fuller, richer. Not deeper bass or higher highs and air all around,
just a more relaxed sound. And this is I presume with CD's broadcast from across town. I have not had this sound on vinyl. Would loading and capacitance have something to do with this? As I don't have any options in this regard.

If your cartridge is not properly loaded, you are missing a bet with LPs. Proper loading can take out a lot of harshness and improve detail.

If the cartridge is a few years old, the cantilever suspension can perish (like bad shocks in a car) and the cartridge can get a lot harsher and not track as well. Of course, proper arm setup is *crucial*!
Hi Atmasphere,
The cartridge is new with maybe twenty hours on it. Still, it is a vast improvement on the Shelter 501 I had before in the same set up.
I think you are right, it has to be the loading of the cartridge.
It is hooked up to an Audio Interphase SUT which in turn is hooked up to the MM
section of the pre. As for options re set up,there are none. This is where I believe my problem lies.I hear all the detail and all the 'hi-fi' stuff, but it is not as lush and fleshed out as on a cheap FM tuner that I use for background music in the system. It seems as if there may be a better connection between tuner and pre than the vinyl set up and pre to my ear. Even though all the better wires are on the vinyl set up.

Also, I have a cheap 1oo dollar Panasonic DVD player I sometimes use for a CD or two, and it too seems to have a fuller, more direct sound. Not better, not by a long shot, just a livelier more robust sound it would seem.
It's as though the phono signal has gone through the ringer one too many times and come out a little bleached,a little tired.
You just feel like your only getting 50% of the signal instead of the full 100%
like the tuner and DVD seem to put out.
Arm set up is good too. I have the RS A1 Labs arm which plops down anywhere.
I've had it for five years and I've got it dialed in pretty well.