I had a reply ready and only then realized that you've already posted the PSU schematic so I have to amend it 🙂
With so low a B+ you really should consider using red LEDs (again the low luminance type, not the high Vf high brigtness ones !) instead of green ones, or 620R resistor instead of 680R. You should end up with 100V or thereabouts on the anode of first stage.
If it was me though I'd reduce the resistance in the PSU and increase the capacitance accordingly. 6N1P can sustain much higher anode voltage and will perform more linearly with higher current. As for the "optional" capacitor, I'd leave it out since you've got plenty of filtering as it is, it only causes undue stress to the rectifier tube.
Paralleling tubes is unnecessary in your case. It is usually done when more current is needed (when driving a load with too low an input impedance) which is not the case for you. There is no point in doing it besides cosmetics as you already have a nice enclosure with four sockets mounted. This enclosure will come in very handy after a while when you get bored with existing setup and go for something that utilizes all four sections to the full extent, i.e. Broskie's "Aikido".
As suspected, your existing circuit operates in the far right portion of the transfer characteristics of your tubes where they are producing masses of distortion, plus it was making excursions into positive Vg zone if your signal source is a modern audio component (a CD player for example).
in the datasheet it says that the anode supply voltage should be 100v but after the 220k plate resistor i only see about 13v. how do i calculate this. datasheet says that anode current is 15mA so the voltage drop across the resistor is E=I*R, E=.015*220000 ....?????😱
there is a 190v drop through the 220k I=E/R 190/220000= .0009 = .9mA
i guess the tube isnt drawing enough current at all.
is this right. is the tube a dud. yikes
good thing im a patient, easy rollin' mellow dude
Your tube is OK. You started with a 350 volts ps and ended up with 13 volts at the plate. Kind of funny or just plainly stupid, choose one. Don't change the tube, change the circuit. Arnulf posted a good one, didn't he?
But first fix your heater voltage
But first fix your heater voltage
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can you help me to calculate what voltage i should expect at the plate given the e88cc tube in series with a 220k resistor on a 205v B+ rail
yes Arnulf did. i just dont really understand the math involved and im struggling with it. i just want to clarify where my foggy
brain obscures my understanding.
i want to understand mathematicaly what is going on, im tired of going around blind bumping my head and stubbing my toe. i dont mean to cast doubts on anyone's sincerity and i dont want to appear ungratefull.
i trusted the initial designer of this amp to send me a kit that i could assemble, inhale some flux vapours and plug in to my ears delight.
i would like to see some equations to help me understand better.
i ordered all the parts to build Arnulf's circuit and i trust that it will work well as much as i trust anyone to give me good advice. i am in no way trying reflect negatively on anyone, i always hope for and assume the best.
Mathematically, strictly speaking, I would divide existing schematic by infinity, then add a new one well designed.
OK chopchip, it's easy. Look for Ohm's Law in this useful little program. You'll understand.
Electronics 2000 | Downloads - FREE Software
Electronics 2000 | Downloads - FREE Software
Huh?? That isn't right. 15 mils across a 220K resistor is 3300Volts!
The datasheet is giving you the maximum do-not-exceed current. This means that you can set the idle current (no signal) at no more than half that value. Also the datasheet maximums are such that you can only hit one at a time- IOW if at max current, then you can't do max voltage.
If your power supply is 200 volts or thereabouts and your plate voltage is about 100V, then we have the voltage across the resistor at 100V, that divided by the 220K resistance is only .45ma. The tube is **starving**!
The plate resistor *has* to be reduced. I think we need about 3-5 ma to make this work. If we did 3ma and a 100V drop across the resistor, then the resistor value would be 33K or thereabouts. The resistors in your power supply will create serious voltage drops- so they will have to be changed too. I suspect 2K-5K will be better values once this thing is up and running, but to find out you use Ohm's Law the same way, make sure to include the currents from both channels...
I'm going to disagree with Arnulf on the power supply- I would keep that 33uf input cap as the tube can handle that fine and without it your power supply voltage will drop down to an unacceptable level.
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Grab a copy of Morgan Jones "Valve Amplifiers" and read very carefully the section on load lines. Generally, these things are designed graphically, using the tubes' plate characteristics.
i was hoping you could walk me through it puuleeeasssseeeee.
if it comes as second nature to you could you please show me the calculations. if you have the time of course.
it would help me to verify my understanding
thanks very much.
Since the preamp already has 4 sockets. I'd rework it to reflect Arnulf's schema but use one triode in each tube such that the right channels uses the first triode in each tube and the left channel uses the second triode in each tube. This way you can "cool swap" like Artemis labs does.
computerese:
IOW= In Other Words
OTOH= On The Other Hand
IMO= In My Opinion
IME= In My Experience
IMHO= In My Humble Opinion
YMMV= Your Mileage May Vary
FWIW= For What Its Worth
If you would like a good Tube modeling software, this is the one I use and recomend:
Tube CAD: Tube Audiio Design Software
its $30 or so, but its simple to use.
Doug
Tube CAD: Tube Audiio Design Software
its $30 or so, but its simple to use.
Doug
Hello,
Where theory meets practice there is a point where theory fails to explain the details. Plate curves and load lines are not straight lines; rp, mu and gm are not constants. Theory and math is a place to start, understanding what you know is the goal.
For this current project put on your eye and ear protection, plug it in, measure it, record the data, turn it up until it explodes, go to bed, read, dream about it, adjust your assumptions and repeat the process for the next 30 years.
BTW Keep the transformer.
DT
It is all just for fun!
Where theory meets practice there is a point where theory fails to explain the details. Plate curves and load lines are not straight lines; rp, mu and gm are not constants. Theory and math is a place to start, understanding what you know is the goal.
For this current project put on your eye and ear protection, plug it in, measure it, record the data, turn it up until it explodes, go to bed, read, dream about it, adjust your assumptions and repeat the process for the next 30 years.
BTW Keep the transformer.
DT
It is all just for fun!
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