Diod bap811

[bengt]

Hi !

Can anyone tell me what i can replace D101,D102 with. The number is Bap811 and I have tried to find about it but failur. Is it possible to replace with 1N4148 ???


bengt

 

[dhaen]

As you can see from the attached image (in Polish I think), this is a stabiliser diode with much greater voltage drop than a 1n4148. There must be more common types available today. If not, you could try 3 1n4148's in series.

 

[bengt]

Great !!!

I have search the internet for several days without finding any data for this Bap811 diode.
This is in a preamp and I will try to take 3 or four 1N4148 instead

Thanks for your fast reply !!!



cheers !!!


Bengt

 

[dhaen]

Maybe 3 is closer. I had edited my reply while you posted.

 

[mandat]

BAP811 was produced in UNITRA CEMI (Poland) a few years ago; Zener diode in TO-92 case
IF: 0,05A, Tjmax: 150C, Uz: 1.45-1.65V IR: 1uA for UR: 6V
It means that you can replaced it by 2 ordinary, low power silicon diodes, like 1N4148, coupled in series or even two CE junctions of low power transistors connected in the same manner e.g. BCxxx.
obudowa: TO-92
The link below leads you to a catalogue but in polish language.
http://www.eres.w3.alpha.pl/index1.php?text=25

 

[mandat]

erratum
BE junctions

 

[bengt]

So, this was the only thing left for testing my preamp and I tried with two 1N4148 for each Bap811 and it seems to work well.

But Mandat, you wrote that it is a zener diod. Is it possible to take just one zenerdiode with 3.1 volt instead of this two Bap811 ? just curious.....

Anyway, it seems to work well, thanks to you people here !!!!


Thanks,

Bengt

 

[Eva]

Changing the number of 1N4148 allows to select the operation mode of the output stage

With two 1N4148 it will work in class B, with three 1N4148 it would work in class AB and with more diodes it will work in class A. The optimun number of diodes depends on the load impedance and the supply voltage

The original design appears to work in class AB with 1 to 2mA biasing. I would recomend using at least four diodes or a Vbe multiplier [an additional BC550C/BC560C and two resistors]. A zener may be also suitable

 

[mandat]

I think that two BAP811 (stabilising diode) should not be replaced by one Zener diode (3.1 or 3.3 V) because these devices have different temperature coefficient, and some problems with preamp stability could arise.

 

[Eva]

With 330ohm emitter resistors, even a drift of 1 volt between 'hot' and 'cold' would cause a mere 1.47mA drift in bias current. Not a problem, I think. I would use 5mA bias [or even 10mA also reducing emitter resistors to 100-150 ohms]

 

[bengt]

So, I could try to have 4 1N4148 and reduce emitter resistor to ~150 ohm to have it to work in class A ?

Hmmm... I will try this later tonight

The supply 60V (2x30)

Thanks !

Bengt

 

[Eva]

I was expecting +-15V supplies. 10mA at +-30V causes each transistor to dissipate 300mW. With 233ºC/W junction to ambient thermal resistance this causes the die to be 70ºC hotter than the ambient. With such high power supplies 5mA bias would be a more conservative option [accomplished by four diodes and 150 ohm emitter resistors]

 

[bengt]

Ok, so I´ll go with 4 diodes and 330 ohm emitter resistors


Thanks

Bengt