germanium diodes

[tiges_ tendres]

are germanium diodes similar in terms of quality as germanium transistors?

What I mean is, are they as unreliable.  As in two transistors can leave the same day but one can be great and one can be crappy.

Is this true of ge diodes too?

[petemoore]

You can measure the foreward voltage threshold of diodes.
 Ge transistors and diodes should have close to the same readings, some inconsistancy in both, but not much if used as just a diode.
 Transistors active gain may go up/down with temperature, diodes aren't active and therefore have not gain.

[Paul Perry (Frostwave)]

All the Ge diodes I've seen have been on-spec.
Unless they have been damaged by very clumsy soldering.
I've never struck a faulty unused one.

[Mark Hammer]

I don't know if "crappy" is the right word to use.  There IS some variation within the tolerances/specs of the component, and some manufacturers may have a different spec for the same *numbered* component, so hand selection using a DMM may help to identify components that are "better-suited" to the circuit or tonal goals.

Personally, I find about 100mv range exists within Ge diodes of the same part number.  Is a 1N34 with a forward voltage of 197mv "better" or "worse" than one with a forward voltage of 283mv?  I don't know.  It depends on what you're trying to do.  If the diode is part of something that will set an upper limit on your output level, then 283 *could* be better by virtue of allowing more signal "out".  If there is a means of restoring level after the diode and the tonal goal is harder clipping, then 197mv is "better".  If the goal is providing two complementary half-waves so as to prodce an octave then matching forward voltage becomes more important than absolute forward voltage.

Ultimately, the question becomes one similar to "Which is better, 1-1/4" drywall screw or a 4" cement screw?"  The answer is, of course, "It depends on what you're trying to do and where you're doing it".

[petemoore]

If the goal is providing two complementary half-waves so as to prodce an octave then matching forward voltage becomes more important than absolute forward voltage.
 I figured that's true and measure bunches to find matches in octaves. Not sure how important this is, also not certain how much 'shaping' the values around a diode pair in an octave matters, but I mess with matching and playing with mismatched resistances around or near the diodes. It seems it would matter just exactly how symmetrical the + and - halves of the waveform are going into the 'doubling' section are, i tend to build these sections so that values can be tweeked...but shoot for 'symmetrical matches' in these areas...
 That's my story, and I'm sticking to it until I figure out a better one.

[tiges_ tendres]

Ok, that helps me alot!

I've been having trouble building a buzz box, from runoffgroove.com

Ive pretty much isolated some grounding issues I had, but I still can get it to octave the way it does in the sound clip.

I think its either that the battery isnt fresh enough, or that the diodes aren't properly matching.  Unfortunately I dont have a multi meter to test, nor if I did, have any clue how to use one.

So lets drink a toast to winging it!.  I socketed all the diodes because I figured with a build as easy as this, I was definitely going to encounter some problems!

all of your help is much appreciated

[Mark Hammer]

If the goal is providing two complementary half-waves so as to prodce an octave then matching forward voltage becomes more important than absolute forward voltage.
 I figured that's true and measure bunches to find matches in octaves. Not sure how important this is, also not certain how much 'shaping' the values around a diode pair in an octave matters, but I mess with matching and playing with mismatched resistances around or near the diodes. It seems it would matter just exactly how symmetrical the + and - halves of the waveform are going into the 'doubling' section are, i tend to build these sections so that values can be tweeked...but shoot for 'symmetrical matches' in these areas...
 That's my story, and I'm sticking to it until I figure out a better one.

Your take is bang on.  The complementary matching can take place in a variety ways.  If a series diode is critical, then matching diodes is important.  Looking over a couple of transistor phase-splitter type octave-up units, you can see the following:

Roger Mayer Octavia  Phase splitter made by MPS-A13.  Emitter and collector outputs come out through 22uf caps into a pair of 1N4148 diodes.  Caps are in parallel with resistors.  Matching involves caps, resistors and diodes.

Green Ringer Signal passes through cap/resistor network into diodes.  Matching involves all three.  JC Maillet's modded Green Ringer uses a trimpot to add resistance to collector output for balancing.

Univox Superfuzz  Phase Splitter outputs come through 10uf caps and 470R resistors.  Balancing levels involves resistors.  Balancing it across the entire spectrum involves comparable capacitance.

Fender Blender  Identical arrangement to Green Ringer - CR network and diode prior to mixing.

Ace-Tone FM-2 Fuzzmaster  Identical to Superfuzz except resistors come before caps.

Foxx Tone Machine  Same as Green Ringer and Fender Blender - CR network and diode.

So, sometimes matched diodes becomes part of producing two "anti-clones" of the input from the phase-splitter outputs, but sometimes it's just caps and resistors.  In most instances, regardless of diode matching being recommendable, matching them to within 0.01% does not mean your best efforts will not be undone by 5% resistors and 10% tolerance capacitors.  And conversely, matching the resistors and caps still requires diode matching if diodes are part of the octave-generating circuitry.