[Gallaine]

Ok, so after a very long work week, and weekend, and 250 hours of burn-in I sat down Sunday to do so some critical listening. Lo-and-behold there was static in the right channel. Having read of a dead channel in a previous thread being corrected by leaving the unit powered but with no signal I tried it myself. Turned off the unit over night and turned it back on in the morning. Left it sit for 24 hours with no signal. Didn't fix it. I tried switching inputs. No dice. I tried switching headphone sockets since there are 2 labelled "Pro". No fix. I even tried different interconnects. Nadda.

I'm outta ideas. Any suggestions? The static remains the same no matter what the volume is set at or even whether or not there is a signal. A bad tube maybe?

Help!?

 

[daycart1]

Try switching the tubes left for right. Does the static switch channels? Do you have a backup pair to try?
Good luck.

 

[Gallaine]

I've actually been collecting tubes for tuberolling later once I became familiar with the amp. The problem is that I have to manually bias them and I don't have a DMM. I guess in order to determine if it is a bad tube I'll need to go ahead and get a meter.

There is a current thread on biasing the 007t amp. I assume that the procedure is similar for the 006t but I only have to worry about 2 tubes instead of 4. If someone could give me biasing instructions specific to the 006t I would find that helpful.

Another piece of information is that the static is intermittent.

 

[Hirsch]

The bias procedure is necessary for your tubes to perform optimally. However, it's not going to hurt them if the bias voltage is slightly off for a short period of time. Switching the tubes gives you a quick way to determine if you have a bad tube. Might as well find out...

 

[Gallaine]

I took daycart1's suggestion and swapped the tubes. The static moved to the left channel. So, it seems to be a bad tube. And the good news is that I have plenty of replacements.

I'm going to look up the other threads that descibed the biasing procedure. But, if anyone would care to give detailed instructions here that would be great!

 

[kevin gilmore]

here you go, slightly edited

All the stax tube amps (other than the T2) have 2 pots
per channel that need adjusting when you change out
the tubes.

There actually is no difference in the procedure between
the single tube per channel versions (t1---006) and the
2 tube per channel (007)

One pot is the dc balance between the sections of a tube
(or between both tubes in the 007)
and is measured between pins 3 and 4 of the headphone
connector. (2 and 5 for other channel) Set it to zero.

The other pot is the dc offset and is measured between
pin 3 and chassis (pin 2 and chassis for other channel).
Set it to zero.

You will have to repeat this a number of times to get it right.
Time and temperature will cause drifts...

 

[Gallaine]

Thanks.

I actually found your instructions in another thread and followed it last night. One problem I had was determining what pins 2, 4, and 5 where in the headphone connector; pin 3 was easy since it is in the middle

. It changes of course depending on whether or not you count clockwise or counter clockwise (when looking at the connector from the front panel). Unfortunately the manual did not help answer this question. I had to try and figure it out on my own. If I counted clockwise adjusting the dc balance pot didn't seem to change the voltage reading. Counting counter clockwise seemed to work. I hope that was right, but if not I'll catch it tonight as I wasn't able to get everything zeroed last night.

One embarassing thing is that it took me over an hour to figure out that each channel has it's own dc offset pot. I couldn't see the other one because it is under the large black wires that run to the volume control

. Well, that's my excuse anyway.

I was able to get the left channel zeroed without much drift. I never was able to get the right channel zeroed without drift between 0.5 V and -300 mV. And that was the hard part. Every change induced fluctuations that lasted minutes! And it took me a while to figure out that you only need to adjust the pots by minuscle amounts; and I mean minuscle. After messing around with the left channel for a while I figured out a procedure that seems to work: adjust the dc offset until it close to zero, go back to dc balance pot and adjust it a little, then go back to the dc offset and get it close to zero. Keep doing this until both pots are close to zero and then start the fine tuning. I found this necessary because I'd get the dc offset set only to find that the dc balance was way off.

This was a painful experience. It will be even more painful if I have to do it again because I biased everything using the wrong pins

! Then again I'll start to become concerned since adjusting the pots using a different counting direction for the pins didn't affect the voltage.

EDIT: I also noticed an appreciable difference when measuring voltage between pin 3, or pin 2, and ground depending on where on the chassis you put the probe. I decide to use the external ground post.