It is a 300B amp with the PSU based on the Time Bandit schematic and the rest based on primarily the JELabs design.
I was playing around with putting a CCS on the plates of the 6sn7 to 10mA...couldnt ever get more than 4 or 5. When I fired it up the 5U4G started making a terrible noise and one of the plates went red and the fuse blew.
Unhooked the CCS went back to standard plate load and put in a 5AR4 I had in spare...after about 10 seconds it started arcing and buzzing and I turned it off before the fuse blew...
Put the 5AR4 in a spare amp I had to see if it survived and it didnt...
The only thing I can think is that when the first time I fired up with the CCS I was pulling 79mA from the 300b's and then 10mA per 300b...The power xformer is an allied 6k7VG rated at 150ma so I realized that I was on the edge but the amp ran for many hours with no hiccups albeit hot.
The chokes are also rated at 90mA per "side" so I was maxing those out as well.
The logical places I have looked are for shorts on the caps or chokes but the DMM does not indicate a short...at least if Im doing it right. my DMM does not do capacitence though...I am thinking that when the first 5u4G blew it toasted the 50uF cap(s)...its a dual section JJ 500V unit.
While not ideal I think the chokes might be OK as long as I keep the 300b's below 80 and still shoot for 10 on the 6sn7s.
Thanks,
Carl
I was playing around with putting a CCS on the plates of the 6sn7 to 10mA...couldnt ever get more than 4 or 5. When I fired it up the 5U4G started making a terrible noise and one of the plates went red and the fuse blew.
Unhooked the CCS went back to standard plate load and put in a 5AR4 I had in spare...after about 10 seconds it started arcing and buzzing and I turned it off before the fuse blew...
Put the 5AR4 in a spare amp I had to see if it survived and it didnt...
The only thing I can think is that when the first time I fired up with the CCS I was pulling 79mA from the 300b's and then 10mA per 300b...The power xformer is an allied 6k7VG rated at 150ma so I realized that I was on the edge but the amp ran for many hours with no hiccups albeit hot.
The chokes are also rated at 90mA per "side" so I was maxing those out as well.
The logical places I have looked are for shorts on the caps or chokes but the DMM does not indicate a short...at least if Im doing it right. my DMM does not do capacitence though...I am thinking that when the first 5u4G blew it toasted the 50uF cap(s)...its a dual section JJ 500V unit.
While not ideal I think the chokes might be OK as long as I keep the 300b's below 80 and still shoot for 10 on the 6sn7s.
Thanks,
Carl

