Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => PC Express and JSchem - Schematics and Layout diagrams => Topic started by: Iannone on February 11, 2009, 01:05:59 pm

Title: The Critter - 2 EL34's in SE
Post by: Iannone on February 11, 2009, 01:05:59 pm

Just got her up and running with lots of help from this forum, particularly sluckey.  It sounds good, but a bit bright.  I'm thinking of the following revisions:

1.  Replace the 2 .022 coupling caps with .033;
2.  Replace the two 500 Ohm cathode bias resistors with a single, 10W 240 ohm resistor to make the tubes run just a bit hotter.

Title: Re: The Critter - 2 EL34's in SE
Post by: Geezer on February 11, 2009, 05:35:14 pm

Quote

a bit bright

Try removing the 25uf bypass cap on the final (V2B) driver cathode (it's mis-labeled, but the 12AU7 triode right before the output tubes).
I doubt any of the changes you mentioned are going to tame the brightness any......

You could also try raising the value of the grid stoppers of the EL34's a bit more (100k? or more?) just to see if it smoothes out the brittleness.....

$.02

Geezer

Title: Re: The Critter - 2 EL34's in SE
Post by: Iannone on February 16, 2009, 03:20:54 pm

Geezer:

I pulled the bypass cap from V2B, replaced the 12AT7 with a 5751, and I am now good to go.  Thanks for the suggestion, it helped a lot.

Here's the revised schematic