I've never been quite happy with the sound of the Jonathan Noble PP 300B since buying it earlier this year from KJS . The first improvement I found was swopping the 5687 in each mono-block out for an E182CC - this made the bass less boomy and improved clarity somewhat . No changes made to existing circuit . I should add that I did try a NOS matched pair of 5687's before the E182CC's ( "special quality " version of ECC82 or 12AU7 - with different pin-out to ECC82 , same pin-out as 5687 , higher GM than either ).
5687 : http://www.r-type.org/exhib/aaa0436.htm
E182CC : http://www.r-type.org/exhib/aag0112.htm
ECC82 : http://www.r-type.org/exhib/aai0081.htm
Next I thought I'd try replacing the rectifier , the 5AR4 . I ordered a pair from the Tube Depot ..... these didn't arrive , and the subsequent pair Tube Depot sent also haven't arrived ! So I thought it time to try a " cheap " Russian equivalent ( a quarter of the price ) . I won a pair of NOS 1979 Svetlana 5C3S's on a fleabay auction for round about $20 incl shipping . I popped them in today and WOW! , the Noble PP 300B sounds spectacular . Background noise has disappeared , and the amps sound extremely musical , a smooth and effortless sound . I'm ordering a backup pair or 2 right now !
5AR4 : http://www.r-type.org/exhib/aaa0997.htm
5C3S : http://www.drtube.com/datasheets/5c3s.pdf
GZ34 : http://www.r-type.org/exhib/aaa0013.htm
The really good part of this story is that I managed ( for now ) to side-step having to buy a matched quad of 300B's ( about R6-7000 to land a cheap set here ! ) . If only there was a russian equivalent to the 300B , and I don't mean the EH's .
5687 : http://www.r-type.org/exhib/aaa0436.htm
E182CC : http://www.r-type.org/exhib/aag0112.htm
ECC82 : http://www.r-type.org/exhib/aai0081.htm
Next I thought I'd try replacing the rectifier , the 5AR4 . I ordered a pair from the Tube Depot ..... these didn't arrive , and the subsequent pair Tube Depot sent also haven't arrived ! So I thought it time to try a " cheap " Russian equivalent ( a quarter of the price ) . I won a pair of NOS 1979 Svetlana 5C3S's on a fleabay auction for round about $20 incl shipping . I popped them in today and WOW! , the Noble PP 300B sounds spectacular . Background noise has disappeared , and the amps sound extremely musical , a smooth and effortless sound . I'm ordering a backup pair or 2 right now !
5AR4 : http://www.r-type.org/exhib/aaa0997.htm
5C3S : http://www.drtube.com/datasheets/5c3s.pdf
GZ34 : http://www.r-type.org/exhib/aaa0013.htm
The really good part of this story is that I managed ( for now ) to side-step having to buy a matched quad of 300B's ( about R6-7000 to land a cheap set here ! ) . If only there was a russian equivalent to the 300B , and I don't mean the EH's .
