Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jjschessmaster on June 02, 2025, 09:59:03 pm

Title: 5881 Cold Bias Help
Post by: jjschessmaster 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

Title: Re: 5881 Cold Bias Help
Post by: Esquirefreak 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

Title: Re: 5881 Cold Bias Help
Post by: jjschessmaster 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