GuitarsByDelaney wrote: ↑Fri Mar 27, 2020 7:46 pmI was just curious about whether there was a particular rationale for the CT location vs. any other possible point
Strictly a choice for convenience.
GuitarsByDelaney wrote: ↑Fri Mar 27, 2020 7:46 pmI was actually just reading about the one ohm resistor biasing method yesterday on the EL84 World website, which is interesting to me as I used the OT resistance method most recently on my Fenders. This seems quicker and more accurate.
Quicker and safer. But you have to remember the current at the cathode includes screen current along with plate current. Screen current is a small percentage of overall current, so it's not a big deal. If you bias to X using this approach, you'll actually be a little under your target.
I build and repair tube amps. http://amps.monkeymatic.com
You could also just measure with the most accurate DMM you've got and find two that read exactly 1.0 or very close. If not, it's not the end of the world, you'll be able to record the actual value if needed and do the math, so if you measure 1.1 ohm its;
mV * 1.1 = mA
or just be lazy and assume since it's so close the mA is pretty close.
Also that method doesn't eliminate screen current so you, in theory have an additional ~5mA of safety fudge factor there that's 'on top' of the acutal anode current you're supposed to base the bias on, so you'd be a little lower than whatever you're aiming for.
xtian wrote: ↑Fri Mar 27, 2020 8:30 pm
Strictly a choice for convenience.
I +1 this one, I once built my marshall dual with them under a board in a particularly BAD spot and paid the price. To fix them I had to dig them out carefully and painfully, and then I put them back in a different location that was easy to replace. They had burned up in a PT failure, so I was needing to remove the dead ones and then add in a new PT
I dunno if y'all are familiar with Rob Robinette's website, but he's got these fantastic step-by-step walkthroughs of several Fender circuits and tons of breakaway pages with in-depth looks at all kinds of circuit elements and how they work. It's an awesome website that's completely on topic for someone like me who's interested in amplifier electronics while also getting exposed to foundational science. Despite reading lots of it many times much is still Greek to me, but I'm continually learning and I love it.
It was on his site I saw the artificial CT concept installed on a power tube socket. Looks like as good a place as any and I may just employ it in this build as opposed to running it off the lamp.
Any pictures of the power section and power tube sockets would be appreciated. I can slowly read music and I can sort of read a schematic, still learning on both...
The choke leads aren't long enough so I'm going to have to extend those but I think everything else reaches.
Look at the power supply layouts of the dumbles. They're all pretty consistently similar, but in this case the board lets you put the screen resistors on it, so you don't have to try connecting them yourself. (i.e. some put them on pin 4 to connect over to pin6 etc, but you can just run the leads from the board over to the pin directly as the screen dropper is on there)
Also make sure you look up the pinout of the tube you're using to make sure you get all the right things connected as well.
Make sure you tin (apply solder to) any stranded wires before screwing them into those green terminals. You will also benefit from retightening the screws after playing for a few hours.
Power wiring stays the way it came, stock. From wall voltage, black and white AC wires go to power switch. From power switch, black (hot) goes to fuse, then to PT; white (neutral) goes directly to PT.
I do not use Standby switches in my builds, so I just added a wire jumper to the PCB where the Standby switch pads are.
2019-Monkeymatic-Pinnacle-#1-04.jpg
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I build and repair tube amps. http://amps.monkeymatic.com
xtian wrote: ↑Tue Mar 31, 2020 2:28 am
Looking good!
Make sure you tin (apply solder to) any stranded wires before screwing them into those green terminals. You will also benefit from retightening the screws after playing for a few hours.
Power wiring stays the way it came, stock. From wall voltage, black and white AC wires go to power switch. From power switch, black (hot) goes to fuse, then to PT; white (neutral) goes directly to PT.
I do not use Standby switches in my builds, so I just added a wire jumper to the PCB where the Standby switch pads are.
2019-Monkeymatic-Pinnacle-#1-04.jpg
Thanks, it all made sense and clicked when I looked at it after you gave those directions. I saw the circuitry and its appropriate paths.
Definitely tinning all my leads. It's moment like these when running all the sockets and pots I realize how much I like pre-tinned wire vs. stranded. It just makes it go so much faster!
Do I need to jumper the standby then if I omit the switch?
If you omit the standby switch, yes, you must jumper the pads on the PCB.
You did not put the 5K6 grid stoppers on your power tube sockets. Look again at my photo. The 5K6 resistors go on pins 5 and 6, and the green wires go to pin 6 (I know the silkscreen legend on the PCB says pin 5, which is the ultimate destination...but the signal needs to run thru the 5K6 resistors before arriving at pin 5).
On your preamp tubes, it's ok to cluster each triode's leads together (pins 1-3 and pins 6-8) but separate these two groups from each other a little more.
I am reminded that this project is not for beginners! Many of these things are implied, but not specified explicitly.
I build and repair tube amps. http://amps.monkeymatic.com
