Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shooter on November 17, 2016, 11:08:56 am

Title: fixed bias ?
Post by: shooter on November 17, 2016, 11:08:56 am
Probably a slap me upside the head ? but...
If I have a 50VAC tap and I want 58vdc as center, my brain says a single diode - cap won't cut it, but a bridge plus fat cap would?
am I on the right page?

thanks as always
Title: Re: fixed bias ?
Post by: PRR on November 17, 2016, 11:38:14 am
The peak of a 50.0VAC wave is 70.7V. A simple diode and cap will catch almost 70V DC.

A 50K pot on top of a 100K resistor gives a range like 69V to 45V, with 58V nearly in the center.
Title: Re: fixed bias ?
Post by: shooter on November 17, 2016, 08:27:50 pm
Quote
The peak of a 50.0VAC wave is 70.7V
thanks,
for some reason I thought bridge did the 1.414x, but single diode did .9x - makes life easy
Title: Re: fixed bias ?
Post by: PRR on November 17, 2016, 10:54:52 pm
Diode to cap is 1.4.

Diode to choke to cap is 0.9.

X2 or /2 depending how you count CT windings or doublers.
Title: Re: fixed bias ?
Post by: shooter on November 18, 2016, 08:36:19 am
Thank you again, that nugget is now in my achieves!
I'll try and send you the 70 weather from here!!
Title: Re: fixed bias ?
Post by: PRR on November 18, 2016, 03:39:01 pm
> send you the 70 weather from here!!

Thanks. I'm hustling to re-hose my backhoe because the 50 degree weather is ending and at 40 degrees it gets tougher to work with old/cold fingers. I did put a washer pump in the Honda, but the plow-truck seems to have eaten another fuel pump.
Title: Re: fixed bias ?
Post by: shooter on November 18, 2016, 06:59:51 pm
Quote
gets tougher to work with old/cold fingers
uh huh!  you got 1-2 days then Canada is gonna add it's 2cents to our weather
Title: Re: fixed bias ?
Post by: pompeiisneaks on November 18, 2016, 09:23:27 pm
Not to derail this thread more, (ok nvm I am) but an old coworker lives in Upstate NY and its 72 there today :P

~Phil