Just used a 16 years old new tubes.

[Alan0354]

I bought a pair of Ruby 6V6GT new in 1997 but never even use them. It was in a shed in the back yard for years. I put it in my amp few days ago and it did not sound good. It's look it was farting when cranked. As I experiment with it more and more, it seemed to sound better and better. Someone told me that if a tube has been sitting around for a long time, it takes time to burn in and sound better after that. Is there any truth about that?

[soundguruman]

I bought a pair of Ruby 6V6GT new in 1997 but never even use them. It was in a shed in the back yard for years. I put it in my amp few days ago and it did not sound good. It's look it was farting when cranked. As I experiment with it more and more, it seemed to sound better and better. Someone told me that if a tube has been sitting around for a long time, it takes time to burn in and sound better after that. Is there any truth about that?

I think your bias is set too cold for the tubes.
I think you are hearing crossover distortion. That's the farting noise.
Heat up the bias setting and I think the sound will clean up.

[Jazz P Bass]

I bought a pair of Ruby 6V6GT new in 1997 but never even use them. It was in a shed in the back yard for years. I put it in my amp few days ago and it did not sound good. It's look it was farting when cranked. As I experiment with it more and more, it seemed to sound better and better. Someone told me that if a tube has been sitting around for a long time, it takes time to burn in and sound better after that. Is there any truth about that?

The getter inside the tube may have taken awhile to get.

[Alan0354]

I think your bias is set too cold for the tubes.
I think you are hearing crossover distortion. That's the farting noise.
Heat up the bias setting and I think the sound will clean up.

I biased very hot. I ran -33V to -35V at +B=400 at the beginning.

[jbltwin1]

I DO have a question for you though. Did you clean the tube pins before you put them in? That's a LONG time to sit and NOT have some form of corrosion on them. I'm just sayin'............

[g1]

Did you clean the tube pins before you put them in? That's a LONG time to sit and NOT have some form of corrosion on them.

This was my first thought also. Poor connections at the pins could account for the change in performance.
Alan: you need to measure current rather than grid voltage when speaking of bias. The negative voltage on the grid does not give an accurate assessment of idle dissipation. You could put different tubes in there with the same grid voltage and they may end up biased differently.
To accurately see how your tubes are biased you need to measure the idle current and at the same time measure the plate voltage.
Multiply those 2 numbers and you will have the idle dissipation in watts.

[Alan0354]

I did not clean the pins. I did take them out just now and looked under magnifying glass and the pins looked shinny. I don't believe the contact is the problem. But since I have been removing and plugging many times, there is no way to tell whether there is any oxidization at the beginning anymore.

I just ordered a bias probe. Before, I have no easy way to measure the idle current. But DRRI was designed for -37V, biased at -33V cannot be cold biasd.

[Enzo]

But DRRI was designed for -37V, biased at -33V cannot be cold biasd.

Cannot? Read note #8 lower left on the schematic. Voltages are approximate and may vary 20%.

-37v is an average figure, and how hot that makes a tube run is a matter of not only the bias voltage, but also the B+ voltage, not to mention the tubes themselves. Tubes exhibit a wide range of natural current, so -37v on the grid might make one set run pretty hot and another set pretty cool. That is why it is adjustable.

[km6xz]

Oxidation can cause problems with low potential connections like grids in a common cathode circuit with as little as 6 molecules thickness, far thinner than visual inspection would reveal. You probably resolved it by unplugging and re-inserting the tubes.
What did the distortion look like on the scope?

[kg]

16 is a blink of an eye for a vacuum tube.

[bluto]

16 is a blink of an eye for a vacuum tube.

True, some of mine are pushing 70 YO and still sound great. FWIW I bought an old tube extender on Ebay and it works great for checking voltages in a relatively safe way, recently learned through experience myself that the cathode voltage alone is not a good indication of bias/dissipation and now use the plate voltage too...