PL300 series II

[Rick.ta.fied]

Hi all, I'm currently working on one, recapping, and I noticed that C111 was cut out of circuit on both L&R channels. It would appear from schematic that it is used to stop oscillations in the output, but is there a revision at one point to remove them? I noticed in another post C111 is removed (see picture from thread #20) https://forums.phxaudiotape.com/thr...overheating-on-one-side-at-low-volumes.10042/

Can anyone shead any light on this for me as I have seen others PL300 series II with the C111 (0.0027uf ceramic cap) installed on both channels?

 

[Rick.ta.fied]

Out of curiosity I checked a PL300 (not a series II) and the schematic does not show a capacitor directly across the output transistors to prevent oscillation in amplifier, is it possible a previous tech had been looking at the wrong schematic a PL300 rather than the Seriers II? This is the only explanation I can come up with at the moment, anybody with Series II can you check and comfirm the capacitor C111 is or is not installed?

 

[Rick.ta.fied]

I have installed a silver mica 0.0027uf in the C111 location (see pic)
Anybody?

 

[laatsch55]

On all my (4) 300 Ser II C111 is installed..

 

[Gibsonian]

 

[Rick.ta.fied]

Thank you for verification.

 

[Gibsonian]

Nothing in mine

 

[Rick.ta.fied]

Nothing in mine

Gibsonian, I checked out your picture and it's a bit too dark to see if your C111 is installed or not?
Laatsch55 does confirm they are installed in the 4 units that he has.

 

[Gibsonian]

No it’s not there

 

[Gibsonian]

 

[Rick.ta.fied]

Thanks for confirming that Gibsonian, I would think the capacitor would not be needed if there was no oscillation on O-scope, but if there was high frequency oscillation it would prevent the oscillation and self destruction of the amplifier; although it couldn't hurt anything with it in place either.
Anyone with more experience with this issue or amplifier please chime it...

 

[J!m]

I don't know much, but were there other changes that went hand-in-hand with the deletion of those caps?

If they are there on an earlier revision, was that the ONLY change that occurred on the later revision?

Just because some do, and some don't, doesn't really answer if they SHOULD be there or not...

 

[Rick.ta.fied]

When you say earlier version are you referring to the PL300 or PL300 Ser 2?
I checked both schematics and the PL300 did not have the capacitor as where the PL300 Ser2 did have C111? See schematic

 

[Gepetto]

When you say earlier version are you referring to the PL300 or PL300 Ser 2?
I checked both schematics and the PL300 did not have the capacitor as where the PL300 Ser2 did have C111? See schematic

C111 is simply a local power supply bypass capacitor. It does no harm to have this capacitor installed. Really has nothing to do with the loop stability of the amplifier.

 

[Gibsonian]

I bought mine recently, all stock and running it that way for now. Hopefully no oscillation but guessing as old as this is and running fine, very cool, it is not.

 

[Rick.ta.fied]

C111 is simply a local power supply bypass capacitor. It does no harm to have this capacitor installed. Really has nothing to do with the loop stability of the amplifier.

Thank you for the reply Gepetto, my bad about loop stability, any idea why would anyone would cut them out of circuit to begin with as was the one I'm working on?

 

[Gepetto]

No idea comes to mind unless it failed for some reason

 

[Gibsonian]

Upon further inspection, looks like an electrolytic in there. Or are the two holes I've circled is where it should go?

 

[Gibsonian]

I checked your pics Rick, looks like you have the same cans - whatever they are that I've identified and the C111 belongs in the empty holes that you see in my pic. Mine was without or it was removed. When I recap it I will add it back in. If it's a PS bypass cap I like em.

 

[Rick.ta.fied]

I checked your pics Rick, looks like you have the same cans - whatever they are that I've identified and the C111 belongs in the empty holes that you see in my pic. Mine was without or it was removed. When I recap it I will add it back in. If it's a PS bypass cap I like em.

Thanks Gibsonian, your correct about C111 location (2 small circles) , the large circle on your picture is the bias heatsink transistor, (same cans?) not sure what you ment there but the capacitor C111 is not an electrolytic type, it was originally a ceramic disc type .0027uf/150V.
I installed a silver mica .0027uf as seen in my picture (thread #3) rather than a ceramic disc type.