Transistor gain calculations (R.G's transistor tester)

[salocin]

Hi,

Just polished off building R.G's transistor tester:


Just wanting to double check that I've understood things correctly, so hoping someone here will be kind enough to check my workings for me...

Voltage reading with switch open is 0.73v
Voltage reading with switch closed is 2.02v

Gain calculation:
2.02 - 0.73 = 1.29
1.29 * 100 = gain of 129

Leakage calculation:
leakage * 2472 = voltage with switch open
leakage = voltage with switch open / 2472
leakage = 0.73 / 2472
leakage = 0.00029531
leakage = 29.5 uA

Is this correct?

Thanks in advance to anyone who can help.

[salocin]

P.S: http://www.geofex.com/Article_Folders/ffselect.htm is my source for the calculations

[slacker]

Yeah that's correct.

[mac]

if this is the Ge tester I can't imagine a fnished FF. Gold enclosure?

If you like maths this can be helpful:
http://www.diystompboxes.com/smfforum/index.php?topic=45481.0

mac

[mat]

Nice tester !

On R.G.'s document: 'any transistor that shows more than a few micro amps of leakage is suspect'.

'Voltage reading with switch open is 0.73v' -seems to be too much of leakage or is it?

On R.G.'s document:  'Let's say the device really leaks 93uA, and has a gain of 110 - a prime specimen. What happens when we test? We chuck the thing in the socket, and read (93uA)*(2472) = .229V. Then we press the switch, and read 1.330V. To get the real gain, we subtract 0.229V from 1.330V and get 1.101V'

So 0.23V on the DMM means less than 100uA leakage. So anything that reads under 0.5V might work..hmm..

What would be the max voltage with switch open people accept for the transistors for Fuzz Face or Range Master builds ?

On the document: 'How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad.'

Matti T.

[frank_p]

if this is the Ge tester I can't imagine a fnished FF. Gold enclosure?
If you like maths this can be helpful:
http://www.diystompboxes.com/smfforum/index.php?topic=45481.0
mac

This one also:
http://www.diystompboxes.com/smfforum/index.php?topic=66592.msg529316#msg529316

[frank_p]

Oh !
And for the next, you could build this one:
http://sound.westhost.com/project31.htm

[mat]

Nice tester !

On R.G.'s document: 'any transistor that shows more than a few micro amps of leakage is suspect'.

'Voltage reading with switch open is 0.73v' -seems to be too much of leakage or is it?

On R.G.'s document:  'Let's say the device really leaks 93uA, and has a gain of 110 - a prime specimen. What happens when we test? We chuck the thing in the socket, and read (93uA)*(2472) = .229V. Then we press the switch, and read 1.330V. To get the real gain, we subtract 0.229V from 1.330V and get 1.101V'

So 0.23V on the DMM means less than 100uA leakage. So anything that reads under 0.5V might work..hmm..

What would be the max voltage with switch open people accept for the transistors for Fuzz Face or Range Master builds ?

On the document: 'How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad.'

Matti T.

Can someone confirm this above text: 'So anything that reads under 0.5V might work' ?

Thanks,
Matti T.

[salocin]

Nice tester !

On R.G.'s document: 'any transistor that shows more than a few micro amps of leakage is suspect'.

'Voltage reading with switch open is 0.73v' -seems to be too much of leakage or is it?

On R.G.'s document:  'Let's say the device really leaks 93uA, and has a gain of 110 - a prime specimen. What happens when we test? We chuck the thing in the socket, and read (93uA)*(2472) = .229V. Then we press the switch, and read 1.330V. To get the real gain, we subtract 0.229V from 1.330V and get 1.101V'

So 0.23V on the DMM means less than 100uA leakage. So anything that reads under 0.5V might work..hmm..

What would be the max voltage with switch open people accept for the transistors for Fuzz Face or Range Master builds ?

On the document: 'How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad.'

Matti T.

The transistor I tested in that example was definitely the odd one out. Most of the ones I have checked since have read, from memory, closer to 0.3V.

The voltage with switch open relates directly to the leakage, so by determining what leakage you would be happy to accept you could determine what voltage would be acceptable.

[mat]

Nice tester !

On R.G.'s document: 'any transistor that shows more than a few micro amps of leakage is suspect'.

'Voltage reading with switch open is 0.73v' -seems to be too much of leakage or is it?

On R.G.'s document:  'Let's say the device really leaks 93uA, and has a gain of 110 - a prime specimen. What happens when we test? We chuck the thing in the socket, and read (93uA)*(2472) = .229V. Then we press the switch, and read 1.330V. To get the real gain, we subtract 0.229V from 1.330V and get 1.101V'

So 0.23V on the DMM means less than 100uA leakage. So anything that reads under 0.5V might work..hmm..

What would be the max voltage with switch open people accept for the transistors for Fuzz Face or Range Master builds ?

On the document: 'How much leakage is too much? 100uA is common, 200 happens pretty often. More than 300uA means the device is suspicious, and more than 500uA I would say is bad.'

Matti T.

The transistor I tested in that example was definitely the odd one out. Most of the ones I have checked since have read, from memory, closer to 0.3V.

The voltage with switch open relates directly to the leakage, so by determining what leakage you would be happy to accept you could determine what voltage would be acceptable.

salocin, thanks for Your answer. I just hoped that someone would confirm the '0.5V rule'. Ok, now to build a rangemaster and FF !

Matti T.