Hi,
While swapping big output caps on my Scott 388B I incidentally broke a diode leg in the amplifier output section. The diode is marked SR1-5 and described in the service manual as "silicon rectifier". I attached diagram of my Scotts' output section with these diodes marked.
I know very little about diode types and I could use some forum help to choose the right type for replacement - specific to the power output section of the amp. I only know that the diode should be rated for 70V as this is what comes out from the connected transistor.
My questions:
Thank you,
-Peter
While swapping big output caps on my Scott 388B I incidentally broke a diode leg in the amplifier output section. The diode is marked SR1-5 and described in the service manual as "silicon rectifier". I attached diagram of my Scotts' output section with these diodes marked.
I know very little about diode types and I could use some forum help to choose the right type for replacement - specific to the power output section of the amp. I only know that the diode should be rated for 70V as this is what comes out from the connected transistor.
My questions:
- what type of diode is good for amp output section(normal rectifier or maybe Schottky)?
- does material (silicon in this case) matter?
- amperage rating? (my guess 3A might be good enough but I don't really know deciding factor here).
Thank you,
-Peter
Welcome to diyAudio 🙂
Those diodes appear to be connected in inverse parallel across the supply rails and so in simple terms they probably never even come into play. We usually see that sort of thing in lower power circuitry. I would guess they are used as 'catch diodes' in the very unlikely event some weird inductive load caused some transient pulse. The diodes are just a clamp.
So... silicon by default and something like a 1N5408 should be ample. Those are generic common parts and rated at 1000v 3A. They are not critical at all.
Those diodes appear to be connected in inverse parallel across the supply rails and so in simple terms they probably never even come into play. We usually see that sort of thing in lower power circuitry. I would guess they are used as 'catch diodes' in the very unlikely event some weird inductive load caused some transient pulse. The diodes are just a clamp.
So... silicon by default and something like a 1N5408 should be ample. Those are generic common parts and rated at 1000v 3A. They are not critical at all.
And I'll just add seeing as we can't see the circuitry in detail and seeing as those large caps seem to go to the speaker switching. The diodes still perform the same function but are those caps on the rails or are they on the speaker output and the amp is AC coupled?
It makes no difference to the function and parts used though.
It makes no difference to the function and parts used though.
@Mooly Thank you so much for the answer! Looks like I have two Vishay "glass passivated" diodes in my parts box alerady https://www.mouser.com/ProductDetai...uctor/GP30G-E3-54?qs=NyKJzQ80QAzBfkM1/mLxCw==
This is a 400v 3A rectifier diode.
Do you know what "glass passivated" mean? I see on amazon this term mentioned together with "silicon" so I guess the passivation is just a feature of a regular silicon diode?
Thank you again for solving my problem!
-Peterr
This is a 400v 3A rectifier diode.
Do you know what "glass passivated" mean? I see on amazon this term mentioned together with "silicon" so I guess the passivation is just a feature of a regular silicon diode?
Thank you again for solving my problem!
-Peterr
Glass passivated diodes have been around for decades and tbh I've never looked into them in detail although they were common in switching power supplies and high voltage TV line output stages years ago. I always associated them with high speed 'soft recovery' types... because that was always the type they seemed to be in the stuff we worked on.
There's lots of info on them on the web.
From here:
https://forum.digikey.com/t/diodes/12789
There's lots of info on them on the web.
From here:
https://forum.digikey.com/t/diodes/12789
This explains 'clamp diodes' and what they do. Have a look at figure 2
https://www.ti.com/lit/an/snoa718/snoa718.pdf
https://www.ti.com/lit/an/snoa718/snoa718.pdf
Even 1N4001’s are glass passivated these days.
And the old slow types are fine in this application. By the time the current limiters activate, and send voltage spikes to the rail it already sounds terrible. The length of the spike is determined by the stored energy in the VC and it is what it is. So decreasing the recovery time to 35 ns on the falling edge isn’t any real help at all.
And the old slow types are fine in this application. By the time the current limiters activate, and send voltage spikes to the rail it already sounds terrible. The length of the spike is determined by the stored energy in the VC and it is what it is. So decreasing the recovery time to 35 ns on the falling edge isn’t any real help at all.