Preamp Voltage

[surfsup]

I am debating whether to use a large or small resistor between the screens and PI on the rail of the x10 clone and was wondering what effect having lower voltages vs higher voltages across the preamp would have? Here are the proposed calculated values;

Vol w-1k vs 22k
B+1 329
B+2 322
B+3 318 vs 223
B+4 288 vs 193
B+5 273 vs 178

I know, "just try it" but its not built yet and figured maybe some people have some experience here about the change in the amp's character going higher.

As I understand it, more V means load line, and everything else, gets shifted to the right which means more headroom. But what else happens?

[Phil_S]

In general, the lower voltages will give you less clean headroom. Your lower voltages aren't that low. You'll still get some decent clean headroom from the preamp. If you are talking about 12AX7's, those lower voltages might or might not prove to be "better." "Better" is a matter of opinion. In the end, you really do need to try it both ways to know for sure.

Since I don't know what type of sound you're looking for, I can't really say what you'll like better. Your ears will tell you.

[Zippy]

I know, "just try it" but its not built yet and figured maybe some people have some experience here about the change in the amp's character going higher.

As I understand it, more V means load line, and everything else, gets shifted to the right which means more headroom. But what else happens?

This is one of those golden opportunities to exercise some experiments. You have a Supre kit coming, right? Play with the dropping string to V1 - a small rheosat sub'd for the dropping string resistor could be handy.

If you check through the old Fender schematics, you'll note the trend for V1 plate voltages from tweed to brown to blackface era. It's a great starting place. Compare also to Dumble-esque values.

Enjoy!

[overtone]

+1 on those two good replies.

... But what else happens?

isn't the large drop after the screen node typical of the Ken Fisher type of power string & contributes to the whole rolling-back-the-guitar-volume thing?

[Zippy]

isn't the large drop after the screen node typical of the Ken Fisher type of power string & contributes to the whole rolling-back-the-guitar-volume thing?

That's more an effect of the attention to the contribution of the various gain stages. A large drop between power and preamp lets one achieve a stiffer power amp than would be possible if you want "standard" drops and low preamp voltages.

[surfsup]

You have a Supre kit coming, right?

Yea, I think RJ said the first batch were going to be ready in a couple days. But this question was more related to another amp I'm building in the trainwreck forum. I wasn't really looking to compare sounds, just what higher voltages do.

I looked at a bunch of Fender schemos. Not being familiar with all these amps its hard, so I youtubed it. Seems the tweed/brown sounds come from lower voltages with supposed "dirty" tones earlier. The more glassy, edgy sounds come from higher voltages with the ability to get more clean "volume" from the amp. If I have that wrong let me know.

Is there a rheostat less than $30 for this application?