Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on March 09, 2017, 03:27:26 pm

Title: Limited B+ with a VVR - Which is the way to calculate the resistor ?
Post by: kagliostro on March 09, 2017, 03:27:26 pm

A simple VVR we use is this

(http://i.imgur.com/BubXqJy.jpg)

The 47k resistor set the lower voltage that can be reached

if we want we can add one other resistor between B+ and the pot to drop the higher voltage that can be reached rotating the pot to the max

(http://i.imgur.com/Bh8y8Oq.jpg)

I don't know how to establish the value of the added resistor, so I've think to the sum of resistor + pot as a resistor voltage divider

I did a bit of math and to me seems that around 420K will be a good value for that resistor
(assuming 350V B+ and 250V the max voltage to have on the output)

Can I consider that as the right way to calculate that resistor ?

Thanks

Franco

Title: Re: Limited B+ with a VVR - Which is the way to calculate the resistor ?
Post by: sluckey on March 09, 2017, 03:35:35 pm

That's the right answer (actually 418,800Ω), so I assume you did it correctly.

Title: Re: Limited B+ with a VVR - Which is the way to calculate the resistor ?
Post by: kagliostro on March 09, 2017, 05:11:19 pm

Many Thanks Steve


Franco