A quickie

This is just a li'l something inspired by a comment Kingston made in the MILA-1 thread.

PDF

This might appeal to those of you who like a "colored, tubey" preamp.

One question, grid stoppers? Do you start with them, or add only if needed?

I'm curious because you didn't use them in the original One-Bottle, but this design is asking for more gain from the AV7.

Hey thanks newyordave. I had already done a quick redraw of your original one-bottle schematic by hand, based on your tips at the other thread. Feels like back in school again, getting corrected like this. What a great forum.

[quote author="skipwave"]but this design is asking for more gain from the AV7.[/quote]

[edit]

I'm curious of the use of grid stoppers as well. I thought the point of feedback was a trade off between linearity and gain. This modification obviously goes for the non-linear high gain of the 12AV7 with added distortion, without the gain restricting, but stabilising feedback loop.

[quote author="Kingston"]I thought the point of feedback was a trade off between linearity and gain. This modification obviously goes for the non-linear high gain of the 12AV7 with added distortion, without the gain restricting, but stabilising feedback loop.[/quote]

Right, higher gain and lower stability might equal oscillation. The grid stoppers help to prevent that. I was curious if Dave anticipates the necessity in this design. I actually wondered if they were necessary in the MILA, or if they were added during breadboarding and stayed into the final prototype.

What I find interesting is the different values of grid stoppers that different designers use. Each designer seems to find their favorite value and stick to it.

Nice one, Dave. Do you think 5965 tubes might do it in this circuit? I know it´s a little weaker than 12AV7s and might not be that great driving the output transformer...

[quote author="rafafredd"]Nice one, Dave. Do you think 5965 tubes might do it in this circuit? I know it´s a little weaker than 12AV7s and might not be that great driving the output transformer...[/quote]

I swapped them in for the two-bottle for testing (5965A). I didn't detect any remarkable difference in sound or gain, just that they seemed more subjectible to hum in my layout. I would guess with better layout they would be just fine. In fact there seems to be a shortage of 12AV7's here in finland, so I might not even have the choice from now on. Got some phone calls to make tomorrow.

One tube guy also suggested E180CC "as an equivalent". I might try them at some point.

http://www.artsandmedia.com/5965.html I would guess most of those listening test results are audiophool placebo bullshit, but that little spec table is useful.

"If the Amperex was Mid-Summer, the Philips might be early Summer with clean refreshing air and the Mullard might be Spring. The United would be more like the hues and colours of autumn when the brightness had diminished and mellowed."

shoot me if I ever say things like that.

What I find interesting is the different values of grid stoppers that different designers use. Each designer seems to find their favorite value and stick to it.

Click to expand...

I use 220's. the idea is to put a chunk of carbon in front of the grid to act as an rf choke. In solid state circuits, I've used 100 ohm quite well.

You can certainly go with a higher value, but whatever minimum value stops the oscillations and instability, I say.

And everyone knows a tube with a picture of a guy playing a clarinet is gonna sound better!