i tried it again but they still seem to heat up. i only use two diodes on one leg, using two on both legs brings the voltage down too low.
they heat up to about 110F
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In that case you probably need rectifiers with a little more capacity. 5A ought to do the trick.
BTW you really can't parallel rectifiers very effectively. You are better off having a rectifier that has the capacity for the task. I would look at the data sheets for them, as various devices have different forward voltage drops. You can put rectifiers in series, but as a design rule I would not expect the reverse breakdown voltage to be any different. What can be useful about this is that you can use the forward voltage drop to your advantage.
Have you tried silicon rectifiers? They usually have about 0.7V for a Vf. So 2 in series is about 1.4V and they are pretty good about staying that way over the range of current they can handle.
BTW you really can't parallel rectifiers very effectively. You are better off having a rectifier that has the capacity for the task. I would look at the data sheets for them, as various devices have different forward voltage drops. You can put rectifiers in series, but as a design rule I would not expect the reverse breakdown voltage to be any different. What can be useful about this is that you can use the forward voltage drop to your advantage.
Have you tried silicon rectifiers? They usually have about 0.7V for a Vf. So 2 in series is about 1.4V and they are pretty good about staying that way over the range of current they can handle.
i guess i hit a defective diode the first try because it works allright now. i found heat sink that fits well over both diodes.
thanks for the replies
for C4 is .01uF 63v good enough?
im finaly getting around to trying this!
i installed the parallel diodes on the ac heater legs and it has dropped the voltage about 1 volt to just over 6v and the thing makes a lot less noise now but i think i do pick up some radio frequencies i guess the grid stopper will deal with that.
im eager to hear what your design sounds like!
your schematic is on page 8 of this thread
thanks
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No, it is definitely not enough unless you were driving extremely high-Z load (multiple megaohms worth), plus its voltage rating must be high enough, depending on your PSU voltage.
Use 1 uF or larger as stated, 250-400V rating if unsure, preferrably MKP type.
C4 is output capacitor, not input 😕 Its voltage rating is important as it will see half the supply voltage across it.
As for C1, its voltage rating is irrelevant as there shouldn't be more than few milivolts of offset present (way less than 1V).
sorry. yeah i saw that thanks for the info. you are really helping me learn this art. im trying to follow your calculations.
with the 33k plate resistor
8mA=270v
5mA=170v
2mA=70v
this is the load line
operating point at about 4mA with 150v plate assumes -2.5v grid so;
R=2.5/.004
R=625ohms
just like you indicated!!
thanks!!!
the original design has a 220k plate resistor! how can the thing even function with such a low plate voltage.
lol!
Not well 😀 It was tucked down into very nonlinear region so it was mangling sound more than anything else. This is what we've been trying to tell you.
yeah. i know. but im a bit leary about taking other people's word for it. im definately going to apply your circuit.
do you think the cathode follower is even necessary? of what benefit is it since all it does is increase current output thereby decreasing that output impedance and i dont need a lot of current to run the st70.
ofcourse i dont understand what im talking about really but im just fishin' for more info.
thanks
Wouldn't a resistor work better? No switching noise. Diodes can add a "buzz" sound because they make a high frequency (radio) spike 120 times per second. You can try and bypass each diode with a low value ceramic cap. but a low value resistor will do a well as the diode and it keeps the waveform clean
Chop,
On your heater circuit, you should only need one set of 2 diodes on one side of the centertap. The centertap splits the voltage down to +/-3.15v. on each side so when added they are 6.3. 2 sets would double the drop.
On your heater circuit, you should only need one set of 2 diodes on one side of the centertap. The centertap splits the voltage down to +/-3.15v. on each side so when added they are 6.3. 2 sets would double the drop.
so this will get picked up in the audio signal?
maybe i will try some resistors just for fun.
i want to drop 1 volt
1/2.4=.42ohm
each tube pulls 600mA
2.4 amps total
.5ohm resistor
p=I^2/R
p=11.5 watts
is this correct. that is one large resistor!
thanks
The amplitude of the "spike" is so small it's hardly a spike, and the frequency is so high it's also ultrasonic. Even though it happens on each phase reversal, the duration is so short it's frequency is ultrasonic.
Ok, perfect. All the more reason to only use 1 set. I thought I had seen a post about 100 posts back that showed a centertap on your heater circuit. If not, one set is all you need in any case.
I'm listening to an amp this very minute using 2 schottky 5A diodes. They get warm, but that's OK. But you must be certain the amperage rating for yours can handle the circuit total. There is some room for safety if you match the rating because each diode rests for half cycle as the other one carrys the current. Give them a little air space between them for radiational cooling, so they don't transfer heat to each other.
I don't think any of this is necessary since IIRC you're using line level signal source but you wanted a preamplifier with cathode follower output utilizing 6N1P tubes and that's what I gave you schematic for.
People do many things that aren't necessary, I guess this is just one of those things 🙂 If it was me I'd simply install the attenuator into the amplifier if it was missing it.
i tried with one set but the voltage was still well above 6.2 and the second set brought it to just above 6 volts. i read somewhere that this will extend the life span of the tubes.
thanks a bunch for the info!!
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