I'm using the Edcor XPWR124-120 for 300B tubes. It has 640V CT,at 150ma, 5V at 2A, and 6.3V CT at 4A. With the rectifier tube in I get 440V on B+, -292V on B-,and -140 and -145V on the Grid to 300B tube with the pots turned fully counter clockwise. 5842's adjusted to 175V each. So things seem to be checking out. But when I get to where he says to put a load on the output tranny's and put in the power tubes, and my B+ is at +440V I stopped. Is the B+ supposed to be this high with out the power tubes in? I don't want to screw up my 300b's. I only have one pair. So, is 440V on B+ without power tubes in place normal? Should I proceed as it says to and go ahead and put the power tubes in and adjust the bias on them, and plug in a source and let her play. Will B+ drop when the power tubes are put in and biased to something in the 350V to 370V range? Thank you all.
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IT LIIIVES
It lives, and sings beautifully. However after about 4 or 5 CD's I have the 300B Bias steady at .68 on my meters for both tubes. 300B filaments rock steady at 4.88V. B- steady at -243V, but my B+ started low at about 325V and has dipped to 317V after the 4 or 5 CD's. I have the called out 47uf in the C4 position. How do I raise the B+ about 50V?. I would kind of like to keep C4 at 47uf if possible. Any help would really be appreciated. Thank you all.
It lives, and sings beautifully. However after about 4 or 5 CD's I have the 300B Bias steady at .68 on my meters for both tubes. 300B filaments rock steady at 4.88V. B- steady at -243V, but my B+ started low at about 325V and has dipped to 317V after the 4 or 5 CD's. I have the called out 47uf in the C4 position. How do I raise the B+ about 50V?. I would kind of like to keep C4 at 47uf if possible. Any help would really be appreciated. Thank you all.
Looks like you are drawing a bit too much current from the B+, thus the transformer is not regulating all that well.
I'd suggest backing off the bias on the 300Bs to 60mAs each, which should bring the B+ to around 350V (an operating point thatsounds very good too).
Which rectifier tube are you using?
I'd suggest backing off the bias on the 300Bs to 60mAs each, which should bring the B+ to around 350V (an operating point thatsounds very good too).
Which rectifier tube are you using?
Thanks Izo,
I turned down the bias to 60, and the voltage did go up to 350V, so I guess I'm good. Thank you very much. Now to package this little baby up. I used two brds for this amp and cut them in half. So I have the complete power supply separate from the amp. The brds sit about a foot apart, connected by an umbilical. Seems to be working out just fine. I'll post picks when she is done. I'm using a Sovtek 5AR4 rectifier tube.
I turned down the bias to 60, and the voltage did go up to 350V, so I guess I'm good. Thank you very much. Now to package this little baby up. I used two brds for this amp and cut them in half. So I have the complete power supply separate from the amp. The brds sit about a foot apart, connected by an umbilical. Seems to be working out just fine. I'll post picks when she is done. I'm using a Sovtek 5AR4 rectifier tube.
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