ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

previous: gazza Hello all !thanks for the r... -- 2/2/2004 9:35 PM

Re: busy tweaking - where to bias ?

2/4/2004 10:52 AM
gazza	Re: busy tweaking - where to bias ? hi, well it's up and running and seems quite happy; doesn't sound too shabby either. I've swapped the shared screen resistor for two 1K 10W and added a bias pot. B+ is sitting at 370V and i'm got the bias at about -30V for about 25mA measured per tube through a resistor in series with the cathode (so 25mA = idle total current, maybe 22-23mA cathode to plate current = 60% is bias). I may set it a little higher later on. It's hooked up to a 16 ohm speaker via what I assume is the 8 ohm tap. I'm now in the mood for tweaking ! Need to decide if i fancy upping the preamp gain a little. I really need to swap out the 110V PT and put in a proper 240V one, the amp picks up a bit of hum from the step down auto-transformer. G.

2/4/2004 10:52 AM

gazza

Re: busy tweaking - where to bias ?

hi,

well it's up and running and seems quite happy; doesn't sound too shabby either.
I've swapped the shared screen resistor for two 1K 10W and added a bias pot.

B+ is sitting at 370V and i'm got the bias at about -30V for about 25mA measured per tube through a resistor in series with the cathode (so 25mA = idle total current, maybe 22-23mA cathode to plate current = 60% is bias). I may set it a little higher later on. It's hooked up to a 16 ohm speaker via what I assume is the 8 ohm tap.

I'm now in the mood for tweaking ! Need to decide if i fancy upping the preamp gain a little.

I really need to swap out the 110V PT and put in a proper 240V one, the amp picks up a bit of hum from the step down auto-transformer.

G.