Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: phsyconoodler on December 16, 2010, 12:43:54 pm

Title: bias supply for full wave bridge
Post by: phsyconoodler on December 16, 2010, 12:43:54 pm

I have a PT that I need a bias supply for.It uses a full wave bridge rectifier but I haven't built one for this type of recifier before.
  I can't locate a schematic that may be close to what I need.I need at least -50v.

Any insight is appreciated!

Title: Re: bias supply for full wave bridge
Post by: sluckey on December 16, 2010, 01:01:26 pm

You gotta start takin' notes! This come up monthly. Write this down now.    :grin:

Marshall JCM 900 or many of the old blue diamond Ampegs. Or, look on page 5 of this pdf...

http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf

Title: Re: bias supply for full wave bridge
Post by: phsyconoodler on December 16, 2010, 01:28:10 pm

Thanks Sluckey,I do know HOW to do it,it's the math to come up with the right resistor values is what I'm lacking.I never learned how to use Ohm's Law properly. :color:

You are a real Godsend for us morons!

Title: Re: bias supply for full wave bridge
Post by: sluckey on December 16, 2010, 01:36:10 pm

Ain't no math to it. Just copy it exactly. The hard part is remembering where the info is. That's why I write it down and also leave little sticky notes that have clues about where I wrote it down. Here lately though, I've realized that I need a second tier of sticky notes!   :cry:

Title: Re: bias supply for full wave bridge
Post by: phsyconoodler on December 16, 2010, 01:37:54 pm

You definitely have the gift of giving.Of your knowledge.
  It is appreciated!

Title: Re: bias supply for full wave bridge
Post by: PRR on December 16, 2010, 03:21:56 pm

> I never learned how to use Ohm's Law properly.

WHY NOT??! :protest:

However for THIS problem, the math is non-trivial, nonlinear, awkward. _I_ won't try it.

The JCM900 plan WILL work for most audio amps. Just steal it and build it. Don't put tubes in yet. Check that the bias supply gives somewhat higher (more negative) voltage than you think you need. Now tube-up and tweak.

Title: Re: bias supply for full wave bridge
Post by: phsyconoodler on December 16, 2010, 05:07:55 pm

WHY NOT??!

Because I don't design that much stuff;more of a plagerizer really.I ALWAYS check bias voltage before I put tubes in.
  It's like memorizing the color band system on resistors.I just measure them.
 while you and sluckey were learning that stuff I was racing Motorcycles,cars and Karts.The only math I used was for dew points and barometric pressures into horsepower formulas for altitude-corrected horse power on my Dyno.
  I'm really not that stupid,I just spent a large part of life working out different problems. :smiley: