Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dpm309 on July 03, 2020, 04:37:30 pm

Title: Speed Twin Bias Setting
Post by: dpm309 on July 03, 2020, 04:37:30 pm

What would be a target bias setting for a 100 Watt TE Speed Twin using KT77s. Swapping out the original 18 YO EL34s. The bias probe and adjustment pot are easily accessible from the rear.

Title: Re: Speed Twin Bias Setting
Post by: SILVERGUN on July 03, 2020, 05:32:39 pm

You need to consider plate voltage to determine proper mA

Title: Re: Speed Twin Bias Setting
Post by: dpm309 on July 03, 2020, 05:44:05 pm

Plate voltage is about 425VDC. I reinstalled the Weber bias Calculator (hard drive crashed and lost all of my bookmarks) and according to it, I should be looking at 35mA. I read that you can bias the KT77s a little hotter, so I might go for closer to 40mA. Sorry, should have checked the bias calculator first.

Title: Re: Speed Twin Bias Setting
Post by: SILVERGUN on July 03, 2020, 05:51:37 pm

That sounds good. No need to be sorry. Its just you cant tell one without the other.

Title: Re: Speed Twin Bias Setting
Post by: dpm309 on July 03, 2020, 06:21:24 pm

 Thanks,