• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

tubes n needles


2004-08-28 1:38 pm
Hi everyone.

i'm going to mount a needle- level meter on my HBW amp, monitoring signal on line stage input. Driver is simple, a buffer/opamp rectifier drive a peak-envelope filter.

So i wonder... how it can be done with tubes? i know it gotta be difficult, and expensive, definitely not convenient; but i'm really curious: does anyone have some vintage schematics?:cool:
If you want to use a meter with tubes, use 6AL5s for signal rectifying diodes (or 1N4148 if you don't care) and do it passively, or add, at worst, a preamp/driver stage consisting of a gain stage with cathode follower hanging off it. Or you can put the diode(s) before an amplifier, though you have to pay more attention to DC stability. You might want to read up on VTVM (Vacuum Tube VoltMeter) schematics, too.