6GF7A for preamp circuit?

[Blair]

I have a sleeve of these, and they look like they would work just fine as a preamp tube. Gain of tube 1 is 64 and 2 is 5.4.

Maybe a VA (tube1) into a CF (tube2)? Or even the other way around? One thing that is difficult about preamplification is taming the gain. Even an SRPP with the 12AU7 is too much for most amps, and you can barely click the potentiometer to 9 o'clock with an average 1V to full output amplifier.

So maybe VA using the 5.4mU section into a CF using the higher gain tube?

With the higher mU as CF, would that sacrifice the benefits of the CF lower output impedance?

I'm actually going to build a preamp for myself for once, and want to try something different:)

Thanks!

Blair

[Geek]

Spud amp!

[Blair]

Right, but what about line level with this guy?

I know it is essentially a 13EM7 in a novar base.

I just thought it may be a wicked line level amp. Or any issues?

Blair

[Geek]

I've done a lot of work with these types in general and you'll need a preamp. A (now rare) 6FD7 has the same power triode, but a gain triode similar to a 12AX7 and is the heart of my workhorse.

Here's a page from the dear fellow (RIP) that inspired me
http://dogstar.dantimax.dk/tubestuf/miniblok.htm

Cheers!

[TerrySmith]

I have thought of a preamp using this type of tube. Maybe a gain stage using the higher mu section and a CF with the power section. If you have too much gain possibly add some feedback?

[Blair]

Yes,

That's my thought too. I'm going to toy with the idea and maybe breadboard before I actually commit to drilling on this.

Thanks,

Blair

[Geek]

That should be able to drive nails

My experience too is that those tubes aren't that microphonic as a line stage

Actually, rather than NFB to reduce gain, I've successfully used a voltage divider between the gain and CF stage.... reduces noise w/o altering sonics.

As a plus, you can tweak the frequency response a bit rather easy with a divider to compensate for a boring amp or long cable runs.

Think of a guitar amp's "bright" switch