Author Topic: Bias Advice for: Model T and 2000s  (Read 3141 times)

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Offline N2000s

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Bias Advice for: Model T and 2000s
« on: November 04, 2014, 09:21:20 pm »
I just picked up a 73 Model T. I replaced the tubes with Gold Lion KT88's. I used a bias probe and multimeter. I had read somewhere years ago to bias around 50ma. Does this sound about right? Also as a side note my 1970 2000s was biased to around 29 on the original Tung-Sol 6550's. Any amp techs out there to give some feedback about biasing with a multimeter and bias probe and what's a good range to bias the KT88's in a first gen Model T or in the 2000's amps?

Offline BassHog

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Re: Bias Advice for: Model T and 2000s
« Reply #1 on: November 05, 2014, 12:04:54 pm »
Bias depends on the plate voltage, you cannot just bias to a "ma" number without using the plate voltage to calculate the proper draw per tube.
You can use some of the bias calculators online to help you figure it out.

http://www.webervst.com/tubes1/calcbias.htm

right at the top of that link there is a section where you select the tube type, put in the plate voltage and it will give you the draw in "ma". That is per tube so if you have more than one pair of output tubes you need to factor that into your final "ma" draw per side.
There are also some tables toward the bottom that will give you some baseline settings for cold, avg, or hot by tube type and plate voltage.
67 Sunn Solarus
70 Sunn Sceptre
71 Sunn 350B

Offline N2000s

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Re: Bias Advice for: Model T and 2000s
« Reply #2 on: November 11, 2014, 02:59:53 pm »
Great, thanks for the help and link. I had biased the Model T with Gold Lion KT88's @50ma. All seems fine but I will check the chart to see if that's a good ballpark.