So i just finished up my
EL84 SIPP OddWatt amp.
It sounds awesome! no hum!....
Ill post up some pics later after i get them off my camera...i took a lot of pics
I do have a few issues however..
For starters, the balance between each channel is not quite right, but i attribute this to a faulty dual gang input pot, i tested it with my meter and each gang doesn't read the same resistance except at either extreme of the travel. Its not that each gang is log or lin, they are both log, but one reads improper from about 10%-90% travel, hardly changing at all, then it will jump at the extremes to the proper value....so i think its faulty...I'm in the process of getting a new one.
Second problem..more serious...since i don't have a UL output tranny, i used a DPDT switch to change between pentode and triode strapped configs. As per gofar99's advice, i used a 1k resistor from the shield to the primary winding of the OPT or to the center tap. Now only on 1 channel, and on one of the tubes, the 1K resistor gets very very very hot, and burns up....this however doesn't prevent the amp from playing music....
Am i doing something wrong? i checked the wiring for each channel and they are the same...so why is only 1 resistor burning up...and why doesn't it prevent music from being played.
Last issue for now...tube bias...so in another post i made the newb mistake about how i correctly bias the tubes, but gofar's design...i think...is nearly like a fixed bias, using the LM317 as a const. current device. Now i do realize that no two tubes are exactly the same, so there is an adjustment pot built in as well as 1 ohm resistor as a test point...my question is, the 1ohm resistor is only on one side of the pot...how can i ensure that equal current is going to each tube??? because doesn't the pot act like a voltage divider? shouldn't i need another 1ohm resistor on the other side to the other tube and use both as a test point?
Anyways, see this thread for my past issues:
viewtopic.php?f=9&t=1232and i got my plan from this page
http://diyaudioprojects.com/Tubes/EL84- ... -Tube-Amp/ - in the circuit diagram it is the inserted 1K resistor off pin 9 on the bottom EL84 tube (the one grounded through the 220ohm resistor)