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Low power setting? ...210-65


Posted on Friday, February 25, 2005 - 09:47 am:   


I just got my 210-65 back from my amp tech. He replaced the blown OT with a Mojotone OT, now it sounds great. What an amp!

Could anyone help with a couple of questions?

1) I asked him about the power differences between high and low power. He tested the watts...my high setting produced 50 watts, the low setting produced 16 watts.

Is this about what other amp owners have experienced?

Low being about a 1/3 of the high?

2) Just out of curiosity, how does the low power setting work, and how does the tube biasing factor in? I know that you bias the amp in the high setting, with approx. 700 volts. Then, is it true that the low power setting reduces the plate voltage? If that's it, how do the tubes remain properly biased at this lower plate voltage? Seems like with a lower voltage, the tubes would act much differently, and would require re-biasing.

thanks for your thoughts - - -

michael kaus
Posted on Friday, February 25, 2005 - 03:16 pm:   

It should be more proportional at true output. The thing is, at what % of dist. The amp will break up earlier at the low power setting therefore skewing the reults. THe power is switched in the primary coils so the voltage produced in the secondary changes as well. this means the bias voltage will change as well, proportionate to input voltage, That's whay no rebias. The thing is, depending on how your amp is biased, it can produce distortion at very low power outputs if under biased. Get a little more info from your <tech> and let us know. Maybe we can give yo a little better opinion. By the way, my 2-10 65 breaks up earlier on low than high so that can change the way you look at it. Mike.
michael kaus
Posted on Tuesday, March 01, 2005 - 04:42 am:   

By the way, you might ask your <tech> how he biased your amp. Too many yuppies think it's juist another EL amp and bias them like you would a marshal or anything with EL's and it's usually smoke city. If he's biasing by cathode current, per tube it should be around 21-23mA and you will make it last. Mike.