Welcome To the Hoffman Amplifiers Forum

September 06, 2025, 12:56:08 pm
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: 5881 Cold Bias Help  (Read 623 times)

0 Members and 1 Guest are viewing this topic.

Offline jjschessmaster

  • Level 1
  • *
  • Posts: 7
  • I love Tube amps
Hoffman Amps Forum image
5881 Cold Bias Help
« on: June 02, 2025, 09:59:03 pm »
Hi All!  I built a soldano slo 6l6 nakid following robrobs layout.  I put 6l6s and 5881s in it and currently have 5881.  All works except bias is a little cold I think.

Bias I'm reading 24ma with 453vdc plate voltage with the bias maxed out.  I think thats around 45% dissipation.  Ideally I'd bump that up some.  How would I modify the amp to get a hotter bias?

https://robrobinette.com/images/Guitar/Soldano/SLO-Nakid/SLO-Nakid_6L6_Layout.pdf

Offline Esquirefreak

  • Level 2
  • **
  • Posts: 390
  • I love Tube amps
Hoffman Amps Forum image
Re: 5881 Cold Bias Help
« Reply #1 on: June 02, 2025, 11:10:29 pm »
Either increase the 470R or decrease the 7k5R. The former is probably easier. Try a 1k.

/Max

Offline jjschessmaster

  • Level 1
  • *
  • Posts: 7
  • I love Tube amps
Hoffman Amps Forum image
Re: 5881 Cold Bias Help
« Reply #2 on: June 03, 2025, 06:54:51 am »
You're the best!  Changed to 1k and I biased up this morning and had enough range.  100% agree not touching that bias pot resistor, I remember more than one frustration wiring that up so the big resistor was easy and accessible

 


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