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Part Testing

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5/16/2003 11:47 PM
Andrew	Part Testing I was wondering what types of tests do builders perform on their parts when they get a shipment. How do you weed out bad footswitches, unmatched tubes, leaky transistors, noisey opamps, etc. What do you do with the failures when you find them ? Send them back, sell them cheap on EBay, save them for maybe another use. Andrew

5/17/2003 2:11 AM

There are two devices you mentioned that I always check. First the footswitches,I always open them up and lubricate everything in there with the lubricant thats already there, springs, plungers contacts etc. Then I put it all back together.If you don't do all this they quite frankly jam and presto - broken plunger as the lubricant is sticky. For transistors I use the RG Keen method for gain measurement - very elegant approach.Simple hfe tests won't work to good on germaniums. When the transistors are selected I place them in my test circuit and run the proper signals in and align the unit for the proper waveform. When all that is done I remove the injected signal power and take a noise measurement with the circuit full tilt. Anything over 5mv I start all over.I should mention this is a fuzz circuit I'm using as an example.

There was a time a few years back when virtually 80% of the transistors I was getting were so leaky they were 4 to 5X the max.hfe values, I returned them to the supplier and said check yourself if you don't believe me, they took them back. Now I buy in bulk from Europe and the odds have improved greatly.

Some of the transistors that exhibit higher than normal gain that are low noise I keep for future use, like buffers where the gain is always a humongous 1. The rest go in a drawer that I will open in 20 years to see if their gains are the same. I got a theory that as germanium ages and oxidizes the hfe's may change, as I can't figure why NOS are so good. Some say the process by which they were manufactured is the key, wet vs. dry methods.

Needless to say my next venture is with silicone. Oh yeh I always check my resistor values also.I use tight tolerance metal film with a color codeing that can be confusing if your not used to them. I made a mistake once where I used a 100k instead of a 1k and it took quite a while to figure out what the hell was going on. One of those unrepeatable errors.

5/17/2003 9:25 AM
zachary vex	change your source if the product sucks. scream and yell if you need your money back. find something that always works. don't settle for anything that isn' t almost perfect, and insist on the best price.

5/17/2003 9:39 AM

Chris ( CMW amps )

Before starting I did look for good suppliers with quality parts , I always use matched output-tubes and every amp is tested by measuring voltages , an on-the-road-test and sound/PLAYING

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Tested/matched tubes ( for example ) are a little more expensive then untested/single ones but it does save some bench-time for my custom-builts .

I think it's risky for you to sell those bad parts 'cause people can recognize you ( kinda like : "hey , that amp/fx-builder did sell me some bad parts" ) .

Contact the supplier in case of bad parts , wrong amounts and/or shipping damage .

Chris

5/17/2003 6:58 PM

I just found out that the supplier that I was getting my footswitches from are no longer going be carrying the switches. Too bad since the switches were good and cheap. I either have to find another supplier or another switch.

All the suppliers I've seen thus far that carry the switch need lead times of about a month to get the switches in which would make it hard for me to reacted to changes in production.

If I decided to go with another switch I'll have to evaluate and stress test it to see if it stands up. Oh joy.

I think I'll go write another article.

Andrew

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