tube burnout

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.

Chears

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*!