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Biasing your Tubes to your Room

As I move down the road of enjoying an all analog system, every once in a while there seems to be some kind of breakthrough accidental or otherwise. Whether it being moving into a quality tube amp, or adding another pair of speakers to the output chain,
today I was switching around my output tubes on my Scott 340B.
I was getting a bit more sound out of my right channel than my left.. and this has been going on for quite some time. Subtle enough to not be overly concerned, but always there
ever so slightly.

However, my readings were spot on as far as millivolts go.

So I decided to just trust my ears and tune the bias screws
to my ears.

I literally took the listening experience to another level.

Now the question remains.. by supplying a bit more juice to the left channel.. is it my ears? the room itself? The tubes?

Ultimately it's a listening experience.. and although using the bias to tune to your room or you.. is not conventional wisdom, it's without a doubt tuned the experience very tight and offering a much more refined listening experience.

While some might suggest I am shortening the lifespan of my tubes, I don't really mind replacing them a year early if the quality of the experience is substantially superior to what the technical specs suggest or insist.

Anyone had a similar experience?
astralography
hifihvn
943 posts
 
First off, are they all the same type/brand of tubes? If different brands mixed, or a tube/tubes getting tired can do something like this.

Next, if they are all the same and good (tubes) , try switching the left and right source inputs and let and right speaker output from amp. If the opposite speaker sounds louder/better, then something is going on at your amp, not your ears. Maybe a resistor or something in your amps bias could be out of spec, if your tubes all match and are good.

Different brand of tubes can sound different when biased the same. Changing the bias to a higher setting might not be good trying to get them to sound the same.

If you bias tubes out of spec, you could hurt your amp to. Overheat and damage transformers or other parts, not just tubes.
hifihvn
943 posts
 
Let me add, there's also a possibility something else is causing it, I'm just going with the most likely causes I can think of now.
lostbears's avatar
lostbears
538 posts
 


You are not solving the problem, you are just covering it up. Swap the right and left side tubes. If the problem switches sides then the problem is with the tubes. Replace them with matched pairs. If the problem does not move then the problem could be with the receiver. Has your receiver been restored at all? If not there may be a problem with it. It is almost 50 years old and some of the components may no longer be in spec or not working properly. I would have it looked over be an expert in vintage electronics. By increasing the bias you are not only putting more stress on the tubes but on the rest of the receiver as well.
astralography OP
51 posts
 
The output tubes are about a year old.. and the amp was properly restored by a well known professional.. however, he is over on the other coast.. so I am reluctant to send it over.

My system has never sounded better than it does now.. so it's hard to want to change anything. The bias adjustment I made was about a quarter of a turn.. nothing too extreme.. just a fine tuning to my ears.

I am just suggesting the question..

trust your voltmeter or your ears?
john_tracy
343 posts
 
By what I've read so far I assume that there is no provision to balance the tubes in the PP pair. After a year of use one tube could be weaker than the other creating a situation where one tube will hog more of the current. You should check the individual bias of each tube to see if they are still well matched. Running a weak tube hard is a recipe arching and failure. I've had a tube (6550) fail under those conditions and short the grid to the plate. Fortunately it only smoked the grid stopper resistor, though it was a 5 buck tantalum. As previously mentioned it could also be a weak input or driver tube. A swap of all left and right channel tubes except the output tubes will confirm this. Then start swapping back the individual pairs to find the culprit.
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