Need help - trying to increase gain by paralleling triode sections

[Saurav]

Just saw a picture of a C3G:

http://w1.871.telia.com/~u87127079/pentodf/c3g.htm

I don't think I've seen that base before, and it looks bigger than an octal.

In terms of the circuit requirements the triode mode looks similar to the ECC99, but with higher mu. I think I can handle the higher plate voltage. I'm not 100% sure how to read the pentode data.

How much larger is that compared to an octal based tube?

[EC8010]

As Brett says, ultimate volume is not about the gain of the amplification, it's about loudspeaker sensitivity, amplifier power, and room size. Sonically, the best electronic solution is when your volume control is only just able to make the following amplifier distort/clip.

[Saurav]

Sonically, the best electronic solution is when your volume control is only just able to make the following amplifier distort/clip.

Understood, but I don't think I'm reaching my amp's peak output. I do need to test that assumption though. I probably get close with my hotter recordings, like the bad 80's pop/rock that I own. But with the music I actually listen to, I get about mid-70s average with the VC at -9dB. Which means that when I want to really crank it up, the VC wide open is *just* a little low.

My speakers are 96-97dB, and my 2A3 SET should be good for, what, 3.5W? I'm running the Sovteks a little hot, so probably a little more than that. My room isn't too large (20x15x8 or so), and the speakers are along a long wall, which puts me pretty close to them.

My DAC is Chris Own's dAck, which has a relatively low output voltage (2V p-p, IIRC). I asked him about gain and he said it's set by a feedback resistor, so I could mod this to give me a higher output voltage if that was the better solution. On the plus side, this means that my CDs aren't a lot louder than my LPs (which used to be the case). My phono stage (Pass Pearl) has about 40dB of gain, with a 10x MC transformer ahead of it (so that's 60dB total), cartridge's output is in the .3mV range. I don't want to go 20x on the transformer because that'll cut the current available to drive the phono stage, and I don't know if that'll get too close to the input overload limit. I changed one load resistor to get more gain out of it, but I don't want to deviate from the design too much because I don't understand what affects or does not affect the RIAA response.

Basically, all of my system is set up for modest gain in an active linestage, except I don't have an active linestage

[Colt45]

that tube youve shown looks like a loktal/loctal. it is roughtly the same dia. base as an octal tube..

loctal has a groove on the centerpin that kind of 'locks' into the socket.. locking-octal i guess is how the name came about.

[Saurav]

Well, it seems that (once again) my assumptions were wrong, and you guys were right

I pulled my scope out and took some measurements tonight. On a relatively loud CD, I get about 2.5-2.6V peaks at the output of the DAC. My linestage is set for a peak of -3dB, which gives me 1.8V peaks at its output (2.5/sqrt(2)). This gives me 5-5.5V peaks at the amp's output with a 7.5 ohm resistor. That's about 4W, which is what I'd expect. I don't have a signal generator, so I couldn't check for exactly when the amp starts to clip. With my test tone CD, I got about .7V input to the amp, and 2.2V out of it. That more or less matches what I saw with the music CD, which means my amp's gain is roughly 20 log (3), or 9.5dB. Does that sound about right for an ECC99->2A3? The problem is with LPs. A loud LP produced about half the voltage of a loud CD. I'll wait till my new cartridge gets here, and then experiment with the phono stage some more. I can try the 20x setting on the MC transformer and see if it has any negative effect on the sound.

Hmm... I guess I wasn't *completely* off though. It looks like I can max out my amp with my loudest music selections. It would be nice if I could do that with the music that's recorded at lower levels too. And adding gain somewhere in the chain would be one way to do that. But like you said, if I want to get any louder, I need a more powerful amp.

Once again, thanks for all the help.

Saurav