Electro harmonix lpb booster with different transistor (bc548)

[PRR]

> it may blow.

Put your finger on it. Is it hot?

(This is for 9V, maybe 25V, stuff. Do NOT finger-test 300V tube amps!!)

[aron]

> Do NOT finger-test 300V tube amps

Yep! Don't do it!!!!!

[antonis]

Measuring voltage across the diode measures 7v exactly. But no idea of wattage, so it may blow.

If your zener diameter is less than 2mm it's probably about 500mV..
If it's about 2.5mm it's about 1.5W..
(but it's a very brute approximation only for comparison between same manufacturer zeners..)

Anyway, your LPB circuit draws less than 1mA(*) maximum current so zener power dissipation should be less than 7mW..
(practically negligible..)

(*)IMHO, such a low current isn't enough for zener proper voltage regulation but in your case it works fine because you DON'T regulate anything - you just use zener for voltage drop..!!
(meaning that any existing voltage ripple before the zener is "transfered" unaltered after it - academically speaking, you make things worse by raising the final voltage ripple percentage..)

Is it possible to achieve this voltage limiting effect with a normal diode?

Yes, but for a voltage drop of v Volts you'll need n diodes in series where n = v/0.6

If you want to lower and stabilize your PS voltage, use a series resistor with a shunt zener, just as sir Mike told you..
(calculate resistor value for, 10mA say, for a voltage drop of your preferance - ignore zener's power rating 'cause it can't be more than 150mW - extreme case of 10mA current and 15V voltage drop..)

[Ryanhardy]

Have a problem again.  Seems the zener only works at controlling a wallwart (about 15v).  But when hooking up a 9v battery (measures 9.2) no current is getting pass the zener at all. But when using two 9 volt batterries in series (about 17 volts), the zener works in regulating voltage again.  Is it just a matter of trying different value zeners that work at regulating both the wallwart and one 9 volt battery?

[Ryanhardy]

I think i know what it is.  There is not enough current with the nine volt battery to activate the zener voltage.  I conclude this because depending on which point in the circuit the zener is introduced will decide if the zener starts to regulate.