Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Balticnoiseforge on May 13, 2024, 07:24:14 am

Title: Ampeg V4b Ultra low switch ( last switch )
Post by: Balticnoiseforge on May 13, 2024, 07:24:14 am

Hallo anyone that has experience with the V4B circuit?

Specific about the ultra low switch and the last bit, ie the C22 0.03 and R59: 5m6
As it is written in the schematic the switch does nothing.

Is this some kind of missprint or what? Is it supposed to break contact between 0.03uF and 5m6? Or is 5m6 supposed to be a antipop across the switch?

Also what does the filter do on its own? ( Disregarding the rest of the ultra low circuit ).

I thought it was some passive bass boosting shelving filter, but couldnt figure it out with values plate output impendence, 0.03uF, 5m6?

Or is it simply a capacitator shunting filter?

So if anyone know about either of the things please enlighten me! 🤓👍

Title: Re: Ampeg V4b Ultra low switch ( last switch )
Post by: Balticnoiseforge on May 13, 2024, 12:14:17 pm

Sorry somewhat found the answer i believe.

went back and looked at older ampegs, found this in Ampeg B15s and as locked in GS-12R , so must be same in the V4B. Ie the 5m6 should be across the switch which means it is a basic anode bypass capacitator. Which cuts abit of treble and therefore boosts bass. 🙄

So some sort of Anode output resistance and the anode bypass capacitator should yield a shelving filter at a certain hZ.