diytube.com

Geez, I realize this project has gone on forever, but I'm actually editing the assembly guide at this point. Almost there.

The big hole up front is bias control. The spare octal socket is for future tube rectifier testing. I recommend using two inch high chassis for the production units - I just happened to have a couple of these aluminum 12X8X3s laying around.

Shannon

Wow, that looks excellent. Nice and big, especially the transformers.

I bet the entire setup will look especially sharp in a 2inch thick chassis.

Why are the power tube holes oversized? Mistake? Cooling? Other?

drew*

nineno wrote:Why are the power tube holes oversized? Mistake? Cooling? Other?

Cooling. It should create a nice chimney effect.

Shannon

Looks great, I was wondering how well it would all fit onto a 12X8 chassis.

What bias current are you running for the KT-90s?

/ed brown

EWBrown wrote:Looks great, I was wondering how well it would all fit onto a 12X8 chassis.

What bias current are you running for the KT-90s?

/ed brown

I briefly tested between 55mA and 60mA, but that was with the 800VCT transformer - dissipating about 30W at idle. I won't fire this one up until I get the other one put together - hopefully tonight.

One note, with my new HP Audio Analyzer, I will start to have top notch gain and distortion data. It is very suprising to see how just a few milliamps less of bias will adversly affect the EL34 and KT90. We are talking twice as much distortion with the odd harmonics skyrocketing. No wonder so many of the old amps, like the Eico HF-87, sounded so good. Of course, that same HF-87 on 124VAC mains today is probably way, way over biased.

Shannon