#1 Yeah, I was (and still am) confused as all hell about those numbers. Sticking to your numbers, and a wide safety margin, I'll just go with this a 390R Ohmite 10W resistor from Mouser.
Will order it soon and get it over here.
Since nobody has come up with a better number, Im sticking to my previous one that the output tubes idle at 25mA/section, 50mA/tube. Both channels together for 100mA.
|Since nobody has come up with a better number, Im sticking to my previous one that the output tubes idle at 25mA/section, 50mA/tube. Both channels together for 100mA.
My reverse engineering of the gain tubes puts them at 6mA/section, 12mA/bottle. Both together for 24mA.
All together for 124mA. At this current the single 390 ohm resistor dissipates about 5W, which requires a little planning to make work but is not impossible. Id buy some safety factor, but wire wound resistors are very easy to find in 10W or even larger power ratings.
|Those 4K 1/2W resistors I got are also getting replaced with 3.9K 2W to be safe.|
1) It works and plays music
2) It has some serious transformer hum
Maybe coupling from the transformer into the signal when you have things on top of each other. Otherwise it is most likely a grounding issue (know from personal experience )
3) It sounds distorted at the top and bottom end
Have you checked ALL voltages? Like B+ but more important the voltages across the respective cathode resistors? Nikongod did some pretty good reverse engineering ... verify those voltages to make sure everything is biased up properly or you will be running your valves biased in areas they are not supposed to make music.
It's all packed up to be moved back to Canada with me. I'm flying out in just 2 days! It's going FedEx across (yes, I know, there will be hefty customs and brokerage fees but it's traceable and USPS won't take boxes this big anyway). I should be able to look at it again in about 10 days.
B+ is 160V and heaters are a steady 6.2VAC. I haven't checked bias voltages but it will be first to look at. Ground looks surprisingly close to the schematic as the "grounds" on the "amp side" are actually all connected to a terminal strip and that terminal strip has a wire going to the star ground.
Well, as I've had this on the workbench for some time and could not resolve the buzzing issue, I've completely disassembled the amp and am going to rebuild it.
The PSU will stay as is as I see nothing immediately wrong with it (aside from the choke and 5V transformer having ground wires attached close by instead of at the star ground (the tower looking thing in the middle, just before the blue/green AC heater wires).
I'll post build photos soon, and any suggestions for how to lay out this build would be much appreciated. I'm currently thinking of building the amp part P2P on the top side again, but as "clean" as possible. A single star ground on the top and a single star ground on the bottom, connected via 1 wire.
I am a little concerned about running the AC heaters so close to signal wires, but not sure how to avoid that at the moment.
Also I was reading that I should have connected pin 9 of the 6N6p tube to ground as it might create buzzing, so that's also planned.
Looking over the schematic, I'm not completely understanding the purpose of the 100uF / 400V caps on pin 7 of the E88CC to ground between B+ and Ground.
Do these need to be as close to the tubes as possible to make sure there's enough current available at all times or can these be a couple of inches away, closer to the star ground?