Transmission1

ch25 wrote: ↑11 Jun 2018, 14:02 Not at all. You can use 40MHz crystal to be more sure

Quick question Chris . Any idea why the 2312/2166 have an extra junction between emitter and collector ?
Sammy

Because it have a protection diode inside. Exactly like on your image.

Hello

2SC2166 is particular case

@+
Claude

ch25 wrote: ↑30 Dec 2019, 20:30 Because it have a protection diode inside. Exactly like on your image.

Yeah , but to protect it against what exactly .

Sorry Against inductive load.

ch25 wrote: ↑31 Dec 2019, 11:15 Sorry Against inductive load.

OK . Thanks . Technical term would be a flyback diode then Chris ? Cheers , and happy New Year !

I guess
HNY

ch25 wrote: ↑31 Dec 2019, 12:50 I guess
HNY

Got that from our old friend Google . I'd never heard of it myself . Or maybe I did back in 83 when I was in college ....

Cheers

I'm intrigued,

So this "flyback" protection diode. Will it potentially blow saving the transistor just that once? Transistor carries on being useful but no more protection the next time?
However you have no way to tell if you have a transistor with 1 or both lives left intact?

Or is it just protection and when that protection is used/gone then the Transistor is gone?

I like its other name "freewheeling diode"

I'm not sure , but I'm assuming that it now physically looks like something like this ... ? (Excuse the crappy Paint editing ..)
If it does , and the diode junction went open , then I presume it wouldn't make any difference . Is the 2SC1969 the same ? I'm assuming that it's only added in power RF transistors ?

Sammy

Diode does not act like fuse. It just shorts unwanted signal.
Many other transistors have built in diode. Especially those for inductive switching circuits.

Thanks Paul & Chris, Diode does not act like a fuse explains it well for me.

The fakes that are coming in from China are probably cheep low power audio transistors, that's why they don't work well at 27MHz.
The Youtube video linked to in the first post will not differentiate between a genuine RF transistor and a audio transistor.

Mike

Crackle wrote: ↑30 Jun 2020, 06:54 The fakes that are coming in from China are probably cheep low power audio transistors, that's why they don't work well at 27MHz.
The Youtube video linked to in the first post will not differentiate between a genuine RF transistor and a audio transistor.

Mike

This is true. But it's entirety down to the individual to do their research prior to buying any transistors including the 1969. If they price is cheap they're most likely cheap copies. Genuine 2sc1969's sell at a premium price these days. The Eleflow CB-20 is a good alternative replacement.

I bought a good few last year from dougie at knights apparently new old stock...