Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on April 06, 2020, 02:57:07 am

Title: Vactrol or LDR - There is one suitable to be used with LDR on catode ?
Post by: kagliostro on April 06, 2020, 02:57:07 am

May be title is not so clear, because of characters limit

I'm asking if you know if there is a Vactrol or LDR (have you a component to suggest) that can be connected to the cathode of a (preamp) tube with the variable resistor connected as RK (not the LED diode)

Or if it will be possible to connect it in parallel to a cathode resistor to vary the resistance ... say from 500R to 3K ???

Thanks


Franco

Title: Re: Vactrol or LDR - There is one suitable to be used with LDR on catode ?
Post by: PRR on April 06, 2020, 01:50:34 pm

What are you trying to do? Change bias? Change gain? Remotely?

Title: Re: Vactrol or LDR - There is one suitable to be used with LDR on catode ?
Post by: kagliostro on April 06, 2020, 02:43:35 pm

Ciao PRR

Change the response of the tube

is something like in the PI of the Egnater Rebel 20, but applied to a stage of the amp

that can be achieved using a simple pot, but rotating the pot will scratch, so the idea to use a Vactrol or LDR

Merlin in one of his books give that solution as an option on a PI circuit

(https://i.imgur.com/6CvIYmB.jpg)

(https://i.imgur.com/EpY79B4.jpg)

Franco