RG's Germ leakage and Hfe tester- quest about a symbol

[jimbob]

Im sure this is an over asked question, but i still havnt got around to making one. (RG's Germ leakage and Hfe tester) Whats the easiest and best way to make one?

I found it on RG's site but i bet there has to be an easier way to test and see what transistors will work in a fuzz face or tonebender rather than just sticking them in a socket.

Thanks

James

[gaussmarkov]

breadboard. 

edit: whoa--that was my 500th post.  i actually have a pic of one on my breadboard here.

[jimbob]

I found this at smallbear: near the bottom of the page and it makes sense except for the symbol thats in between the 1 meg and the base of the tested resistor. Can anyone tell me what that symbol is- kinda reminds me of a switch?

http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

How do I measure Gain?

Based on an explanation of the basics from R. G. Keen, I worked out a bare-bones method for getting an estimate of the static DC gain of a transistor, good enough for sorting devices for the FF and clones. You'll need the following:

    * A DVM
    * a 1 meg resistor
    * a 9-volt battery or power supply
    * a few test leads with alligator clips

The temperature sensitivity of older germanium transistors has to be seen to be believed; when setting up these tests, only pick up the devices using tweezers or wearing gloves. The polarities of the battery and meters are shown for PNP devices; they are reversed for NPN.

First, measure the leakage current:

It may take a few minutes for this reading to become stable. (I swear that some of the ones I have tested are reacting to variations in room temp and/or my body heat!) Record the figure on the meter. This is the leakage current.

Keen has noted that too much leakage makes suspect the long-term reliability of a device. How much is too much? My own spec has always been to reject any device that leaks more than 300 microamps at room temp.

Now apply forward base bias through the resistor:

Again, wait for a stable reading. Record the figure for collector current.

Do the following arithmetic to get Hfe:

(Collector Current - Leakage Current)

__________________________________________________________

Base Current

[gaussmarkov]

I found this at smallbear: near the bottom of the page and it makes sense except for the symbol thats in between the 1 meg and the base of the tested resistor. Can anyone tell me what that symbol is- kinda reminds me of a switch?

yes, that is a switch, if i understand your question correctly.  it's a momentary switch that closes when you push it and opens when you release.  when the switch is open, you can measure the leakage current.  when it is closed, you are wiring in the 1M resistor and measuring the collector current.  use 9 uA for the base current (as an approximation).

on a breadboard you can use a jumper wire for the momentary switch.

i hope this helps, gm

[jimbob]

Thanks - Ill give it a try.

[mac]

read this, it is the generic test:

http://www.diystompboxes.com/smfforum/index.php?topic=45481.0


mac