Germanium diode and regulator ?

[zamproject]

hey

Restoring some old studer module
Have a dead germanium AAZ18 on the modul regulator (aux master send and ret)
is there any reason using germanium over silic at this place ??? (other than it's an old module...)

Schem attached.
Global regulated -22 come from the left, modul rail (0/-10/-20) on the right

i go to put a 4448 to test and i'm back

Zam

 

[JohnRoberts]

I don't see an AAz18 on that schematic but only one diode so I will ASSume you are talking about that.

Germanium will generally exhibit a smaller forward voltage drop so in series with the output you will get a few 1/10th of a volt more voltage.

A GP silicon will probably work OK as long as precise rail voltage is not critical.

JR

 

[zamproject]

Hi JR

the AAZ18 are between fuse and Q1

I'm back from soldering and test
looks ok with 4448
I measure the AAZ18 out of the pcb seems ok (but look black under glass, like blowed...)i also change the fuse (dead)
So it was the fuse, I don't check it before as i got some voltage at output 

you mean the germanium are more stable? over time ? over heat ?

i will say it ist critical here. This part of the module change the regulated single -22v to a dual +/- 10v (relative to -10) for all DOA

 

[JohnRoberts]

Hi JR

the AAZ18 are between fuse and Q1

I'm back from soldering and test
looks ok with 4448
I measure the AAZ18 out of the pcb seems ok (but look black under glass, like blowed...)i also change the fuse (dead)
So it was the fuse, I don't check it before as i got some voltage at output 

you mean the germanium are more stable? over time ? over heat ?

No I said what I mean... the germanium semiconductor junction drops less forward voltage than silicon junctions. Silicon diodes are nominally .5V, germanium 1/10th V or more less than that.

i will say it ist critical here. This part of the module change the regulated single -22v to a dual +/- 10v (relative to -10) for all DOA

Ist?

JR

 

[zamproject]

Tks JR

I'm not sure to understand what you call "precise rail", that's why I talk about "critical"


(and full schematic below)

 

[radardoug]

Its not that critical. The transistor is only being used as a slow rampup or filter circuit. The centre voltage is derived from the two resistors, so they should be accurate.

 

[JohnRoberts]

Tks JR

I'm not sure to understand what you call "precise rail", that's why I talk about "critical"


(and full schematic below)

By precise I mean does the voltage need to be "exactly" the same? The silicon diode will drop a little more voltage than the germanium.

JR

 

[zamproject]

No 
I don't think one module with +/- 10v will have significant difference in sound with one with +/-10.2V
The input modules have another topologies, and line out card have only the resistor divider so it's +/-11V

Resistors are 1% should be ok 

tks both for help an advise !

Zam