Welcome To the Hoffman Amplifiers Forum

September 08, 2025, 04:30:48 pm
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Fixed and self bias  (Read 2233 times)

0 Members and 1 Guest are viewing this topic.

Offline shooter

  • Level 5
  • *******
  • Posts: 11018
  • Karma Loves haters
Hoffman Amps Forum image
Fixed and self bias
« on: December 05, 2018, 05:39:29 pm »
I should know this but don’t!  :think1:
You start with fixed biased amp, and 1ohm Rk for current calcs.

now I up Rk to 10 ohms cuz I want to made things hard, and re-bias the fixed side – if needed.

If I keep uppin Rk n tweaking fixed, can I get to a point where even and odd harmonics “balance”, unintended consequences, or am I just wasting gray matter n cloud space  :dontknow:

 
Went Class C for efficiency

Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: Fixed and self bias
« Reply #1 on: December 06, 2018, 02:26:17 pm »
It's complicated. And maybe not worth much.

Quit picking your brain and apply the soldering iron.

Offline shooter

  • Level 5
  • *******
  • Posts: 11018
  • Karma Loves haters
Hoffman Amps Forum image
Re: Fixed and self bias
« Reply #2 on: December 06, 2018, 03:05:09 pm »
Quote
It's complicated.

 :laugh:
ya, it's stuck in an endless loop!  I'm doing woodworking outdoors so my brain just shuts down  :icon_biggrin:
Went Class C for efficiency

Offline jjasilli

  • Level 5
  • *******
  • Posts: 6731
  • Took the power supply test. . . got a B+
Hoffman Amps Forum image
Re: Fixed and self bias
« Reply #3 on: December 06, 2018, 06:50:44 pm »
Maybe that's what Fender hoped when they went from BF to SF.


Anyway 10R can act as fuse & bias sense.

Offline shooter

  • Level 5
  • *******
  • Posts: 11018
  • Karma Loves haters
Hoffman Amps Forum image
Re: Fixed and self bias
« Reply #4 on: December 06, 2018, 07:25:00 pm »
Quote
10R can act
That's what got the whole mess in my brain started, Willabe's KT88 conversion.  The PA tubes use 10r guessing as the "correct" value for the meter's, Then...........  :think1:
I have a small understanding of amp history, and a quick search only yielded spy vs spy instead of working together.

I'll be getting the soldering gun out soon, gotta wire up lights for my ghetto camper II  :icon_biggrin:
Went Class C for efficiency

Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: Fixed and self bias
« Reply #5 on: December 06, 2018, 07:55:53 pm »
Few power tubes have Gm as low as 1/50r, so a "significant" resistor will be 100 Ohms up.

10 Ohms was standard when good meters read 1.5V on the lowest range. 50mA was 0.5V or 1/3rd-scale, you can read that. With 1 Ohm it is 0.050V, hard to squint on a 1.5V scale. But sweet on DVMs where the natural input is 199mV.

 


Choose a link from the
Hoffman Amplifiers parts catalog
Mobile Device
Catalog Link
Yard Sale
Discontinued
Misc. Hardware
What's New Board Building
 Parts
Amp trim
Handles
Lamps
Diodes
Hoffman Turret
 Boards
Channel
Switching
Resistors Fender Eyelet
 Boards
Screws/Nuts
Washers
Jacks/Plugs
Connectors
Misc Eyelet
Boards
Tools
Capacitors Custom Boards
Tubes
Valves
Pots
Knobs
Fuses/Cords Chassis
Tube
Sockets
Switches Wire
Cable


Handy Links
Tube Amp Library
Tube Amp
Schematics library
Design a custom Eyelet or
Turret Board
DIY Layout Creator
File analyzer program
DIY Layout Creator
File library
Transformer Wiring
Diagrams
Hoffmanamps
Facebook page
Hoffman Amplifiers
Discount Program


password