I have high voltage wires a half a block away and a transformer across the street. The transformer was designed for a 115 vac input. I just measured the line at 121.3 volts. Even if it drops a few volts I'll still be above six volts.
Is there a voltage point at which ripple is inaudible? And ripple is just measuring any AC voltage in the supply correct?
Is there a voltage point at which ripple is inaudible? And ripple is just measuring any AC voltage in the supply correct?
Not to confuse you, but ripple is the ac part of the dc line.
Um.. think of it as a really really small ac wave with a dc offset.
Ac lines can be anywhere from 110 to 130.
Personally i think this thread derailed with the first post (who has a tube with a dc only heater?).
The only reason to run dc heaters is if thats your last resort to get rid of hum. it can be painless if its simple with low current heaters and a lm317 with 12vac in. It can be harder if its 6vac in and you have to crc filter the voltage down to 6.3vdc.
Since you have only 300ma of current needed, you could just get a standard 12volt switch mode power supply(here comes the growns) and use a lm317 (or the newer nicer LD1085)to lower the voltage down to 6.3 using some simple online calculators.
Um.. think of it as a really really small ac wave with a dc offset.
Ac lines can be anywhere from 110 to 130.
Personally i think this thread derailed with the first post (who has a tube with a dc only heater?).
The only reason to run dc heaters is if thats your last resort to get rid of hum. it can be painless if its simple with low current heaters and a lm317 with 12vac in. It can be harder if its 6vac in and you have to crc filter the voltage down to 6.3vdc.
Since you have only 300ma of current needed, you could just get a standard 12volt switch mode power supply(here comes the growns) and use a lm317 (or the newer nicer LD1085)to lower the voltage down to 6.3 using some simple online calculators.
Hello,
Many, most, all somewhere in there. Indirectly heated tubes were designed to operate with AC on the heaters. Ripple is a matter of taste. If I can hear it, it is too loud.
IMHO use regulators on sensitive low level circuits as RIAA or microphone preamplifiers. Otherwise leave it alone. Then fix it if it is broken.
Sagging voltage on your heaters may change the operation of your amplifier in not so subtle ways.
Ripple is that little wave on the pond when you toss in a pebble.
DT
All just for fun!
If you want to get it down you have to crc not ccc. Inbetween each cap add a small .5 to 2 ohm resistor. This will reduce the ripple (why are we doing this again?) alot more then just 1 big cap.
I'm guilty. I already finished the chassis and had it painted when I found that my main transformer wasn't strong enough to do all the heaters. so I found this small 6 volt that would fit inside the chassis. I've never built a voltage regulator and didn't know how much voltage it would cost. Then it came out that the voltage was near perfect without the regulator. If I had more experience I wouldn't have gotten into this situation in the first place. Its not cost its having to modify the painted chassis, again.
But it occurs that if the heaters were meant to use ac then a little ripple shouldn't be a problem. I'm going to finish the rest of the amp and listen to it and see how it works.
But it occurs that if the heaters were meant to use ac then a little ripple shouldn't be a problem. I'm going to finish the rest of the amp and listen to it and see how it works.
Back to the question: Open encl pic. Using these methods:- There are limitations.
1:- One needs a low impedance high current heater winding with LowVf Schottky rects as the cap-input circuit relies on peak currents to charge the capacitor to peak value voltage;
2:- If using a regulator; a LDO type works well, (LM2940 ?) Or even better the discrete circuit shown which has a dropout of around 0.2V, depending on % rippple.
richy
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Re: 6.35V vs. 6.3V versus higher or lower...
I think I remember reading an article claiming that tube life increased by a lot if the heater voltage was reduced (not sure if that was by 15% or 10%...). 15% below 6.3V is 5.4V, which seems way too low to me. 5% below 6.3V is about 6V, which seems reasonable to me.
According to that same article, increasing heater voltage significantly decreased the life expectancy of the tube.
The lesson was that for longer life, the heater voltage should be dropped a little. I usually aim for 6.1V to 6.2V on the heaters.
It's absolutely true that if you decrease the heater voltage, you'll decrease the emission of the cathode to plate in the tube. That makes sense, as the cathode won't be made quite as hot from the lower voltage heater. Plate resistance would go up, transconductance would go down... It would be something like working with an aged, worn version of the tube. So don't reduce the heater voltage to the point that performance suffers markedly...
If unregulated, then the heater voltage will go up and down with mains voltage. If your 6.35VDC from 122VAC mains leaves you with "only" 6VDC from a 115VDC mains, then I wouldn't worry about it. Actually, that might be a good voltage point to run an unregulated DC heater supply.
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I think I remember reading an article claiming that tube life increased by a lot if the heater voltage was reduced (not sure if that was by 15% or 10%...). 15% below 6.3V is 5.4V, which seems way too low to me. 5% below 6.3V is about 6V, which seems reasonable to me.
According to that same article, increasing heater voltage significantly decreased the life expectancy of the tube.
The lesson was that for longer life, the heater voltage should be dropped a little. I usually aim for 6.1V to 6.2V on the heaters.
It's absolutely true that if you decrease the heater voltage, you'll decrease the emission of the cathode to plate in the tube. That makes sense, as the cathode won't be made quite as hot from the lower voltage heater. Plate resistance would go up, transconductance would go down... It would be something like working with an aged, worn version of the tube. So don't reduce the heater voltage to the point that performance suffers markedly...
If unregulated, then the heater voltage will go up and down with mains voltage. If your 6.35VDC from 122VAC mains leaves you with "only" 6VDC from a 115VDC mains, then I wouldn't worry about it. Actually, that might be a good voltage point to run an unregulated DC heater supply.
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That is the headache. I darn't' run the earlier 6550 power tubes, esp the B version at lower heater volts/current; these are more emisson sensitive to heater volts/current variations and the cathode current takes ages to creep up. These tubes like it hot, and they get it. The others, KT88's 6L6 families are far more emission stable. Somewhere I read that under current is more damaging than over current. Will did it out.
richy
Yes I also remember that article in Sound Practices.
I tend to use slightly lower voltage on those IHT - about 6~6.1Vac for those 6.3V tubes - simply by small resistors in series with the supply. I've also used 4.6Vdc on 300B. I got good results, no problem at all, for all these years.
However, I had a not-so-good experience with the lowered-than-rating supply on 2A3 recently. The anode current is directly affected by the emission of cathode, and directly linked to filament temperature, traced back to the supply voltage. These factors are tightly bonded (at least on my EH 2A3). Lower supply voltage gives me lower current, lower gain, and recessed / thinner sound. Once I found it, I fed them with sufficient voltage (and current). Over here, I don't care how lower supply can lengthen its life.
I tend to use slightly lower voltage on those IHT - about 6~6.1Vac for those 6.3V tubes - simply by small resistors in series with the supply. I've also used 4.6Vdc on 300B. I got good results, no problem at all, for all these years.
However, I had a not-so-good experience with the lowered-than-rating supply on 2A3 recently. The anode current is directly affected by the emission of cathode, and directly linked to filament temperature, traced back to the supply voltage. These factors are tightly bonded (at least on my EH 2A3). Lower supply voltage gives me lower current, lower gain, and recessed / thinner sound. Once I found it, I fed them with sufficient voltage (and current). Over here, I don't care how lower supply can lengthen its life.
Hello all,
I've read on the JJ website that the 12ax7 can use either 6.3 volt or 12.6 volt supply to the heaters. If I wanted to use a 6.3 volt DC supply for the heaters how do you wire the tube? If you wire 12.6 AC to pin 9 (center) then the other leg to pin 4 with a jumper to pin 5. Would you just wire to 6.3 volts DC to pin 4 and pin 5 to ground?
Kevin
I've read on the JJ website that the 12ax7 can use either 6.3 volt or 12.6 volt supply to the heaters. If I wanted to use a 6.3 volt DC supply for the heaters how do you wire the tube? If you wire 12.6 AC to pin 9 (center) then the other leg to pin 4 with a jumper to pin 5. Would you just wire to 6.3 volts DC to pin 4 and pin 5 to ground?
Kevin
Hey All,
Amateur here asking an amateur question. If you rectify the heater supply to DC without any serious filtration of ripple would it really matter? I mean originally the heaters were supposed to run on AC. So if most of the current flow is DC with just a little ripple out of the rectifier would you be able to hear that as hum? I mean low ripple is cool but if you can't hear it why would it matter?
Kevin
Amateur here asking an amateur question. If you rectify the heater supply to DC without any serious filtration of ripple would it really matter? I mean originally the heaters were supposed to run on AC. So if most of the current flow is DC with just a little ripple out of the rectifier would you be able to hear that as hum? I mean low ripple is cool but if you can't hear it why would it matter?
Kevin
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