MARSHALL P.A. S/A 50W sag resistors ?

[Colas LeGrippa]

Hi,

I had this beauty on my bench, the circuit seems to be the same as the picture but for the 3 ( light blue/white ) resistors ( caps ? ) . I am wondering if these are sag resistors ?
I couldn't see no traces of removal, in the one I had.
At the same time, does anybody have the schem of this very good sounding amp? It is a MARSHALL S/A xxxxA  P.A. model  ( 1970 make ).

Thanx

Colas

http://www.amparchives.com/album/Marshall/50%20Watt%20Series%201966-1981/1985%20PA%2050W/70%201985%20JMP%20PA%2050W%20SN%20SAxxxxA/slides/mars%201970%204.html

[TubeGeek]

The blue and white parts are 0.22uf capacitors.  I have a Marshall master pa amp that pre-dates yours and has those caps too.

[Colas LeGrippa]

mine is 1970 and doesn't have these caps, what are they for ?

thanx

[Willabe]

For cleaning up the SS diode switching noise. The caps short the hi freq. hash to ground. Those caps used with ultra fast diodes gives a very quite SS rectifier B+ PSU.

Marshall used them in a number of there amps.

KOC is fond of this in his TUT books. Merlin writes of them in his book too.


             Brad    

[TubeGeek]

Brad beat me to it!

[Colas LeGrippa]

I see 2 caps from a/c HV to gnd, no prob about that,  but how's the third one in the amp hooked up to ?

Colas

[Willabe]

Hi Alvin,     

3'rd cap is in parallel with the reservoir cap to ground.


                 Brad       

[Colas LeGrippa]

same value, .22 uF ?

Alvin

[Willabe]

Yes, Alvin.
           

                Brad          

[Colas LeGrippa]

Thanx, buddy.

[Willabe]