What physical characteristics in the tube change the tone (affects the tone's [blank])

Dwayne Eash

Active Member
Apr 23, 2020
Reaction score
No argument there. But trying to equate the sound quality and performance of a tube based on some physical characteristic like the OP asks is a waste of time and money.
Hey bluesky636. You make a good point. However, just based on thickness of glass alone and all else the same, that is a pretty clear sign of improved materials, and suggests an increase of lifespan can probably be expected compared to the thin version.

BTW, to the, all tubes should all sound about the same camp, how does military spec, of the same tube type, fit into the homogenized idea, that if the tube specifications do not vary for the same type of tube, so it should just sound and perform roughly the same?

I think most realize military spec is purpose-built to last much longer than standard spec. So, wouldn't that challenge, if not modify the idea, that how you build the tube differently, should not matter significantly to the sound and performance of the tube, as long as it meets the tube's rated physical specs?

Seems obvious to me that preamp tubes can make large sonic differences from brand to brand, and model to model, and time to time, and amp to amp, and ear to ear. Seems to me it's similar with power tubes, but perhaps the differences tend to be not as dramatic.

For those who say there is not much difference, please list how many different kinds of tube makes and models you've changed out. Seems pretty obvious to me that both power tubes and preamp tubes, have various sonic differences, even in the same tube specification, like 12AX7, or EL34.


Well-Known Member
May 14, 2018
Reaction score
The 6C4 was developed by RCA. Don't know if GEC re branded them.

Will mostly see Mullards for 6C4.

I have some JAN Philips of the 6C4 that were tested and graded.

Now I'm wanting a pair or two of the GEC KT88's (6550) to try out.


Brits make great audio gear!

That's the King right there, going to be a fun day when you get to have a try.

GEC when they made a valve they just got it right, B339 B65 come to mind too.

Yes 6C4 Mullards are superb, I have an M8080 in my SVT and it's perfect.


Well-Known Member
Jan 16, 2010
Reaction score
Yes 6C4 Mullards are superb, I have an M8080 in my SVT and it's perfect.

I had an SVT long ago. Still the most rider requested bass amp for back line.

These days I have a 70's V4B with the 2x15 cab.

The KT88's in the circuit I would use them would need upgrades in the caps to handle the extra power.


Active Member
Nov 9, 2008
Reaction score
Tampa, FL
To simplify what makes tubes sound different form one another is the cathode recipe.

Each tube maker had/have their own 'secret' recipe that gave their product it's sound. For example, Shuguang bought all of GE's tooling for making tubes, yet their tubes sound nothing like what GE's do. That's because GE never sold them their cathode recipe.

Why new cp tubes do not sound like vintage tubes is because a lot of the materials used to make those old tubes, and ingredients to their cathode recipes, has been regulated out of use. Like Lead. Lead is the best sounding of all metals, but it can no longer be used in construction of products. Many vintage audio components and gear used lead in their construction which is why a lot of that stuff sounds better than products made today out of inferior materials.

This is the biggest factor in the difference in sound between tubes. After the cathode recipe, then the rest of the tubes construction comes into play.

Latest posts