I have 2 questions, they might seem very rudimentary but I can not find any direct answer to them.
1. The heater of the EZ81 is rated at 6.3V (6-6.6V spec). I'd like to use a toroidal transformer to power it, however I can only find one rated at 6V. For most tubes it'll most likely be fine, but I read that it is important to to underheat rectifier tubes because often they run close to their current output limit. My question is will this be a problem?
2. I am thinking of using a C-RC filtered unregulated DC to supply the heater for 6H30. From PSUD2 simulation the ripple is at 0.3V. My question is, will this be ok?
Thank you.
1. The heater of the EZ81 is rated at 6.3V (6-6.6V spec). I'd like to use a toroidal transformer to power it, however I can only find one rated at 6V. For most tubes it'll most likely be fine, but I read that it is important to to underheat rectifier tubes because often they run close to their current output limit. My question is will this be a problem?
2. I am thinking of using a C-RC filtered unregulated DC to supply the heater for 6H30. From PSUD2 simulation the ripple is at 0.3V. My question is, will this be ok?
Thank you.
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1. This is quite easy to fix, in practice. Just choose a toroid with a (say) 5A secondary. Trafos are usually rated to give the rated voltage at full load - so at one fifth load or less, you should get plenty of extra voltage. If you get too much, add some series resistance.
If you connect the heater to the dc output though, please remember that the secondary winding of most toroids is the OUTER winding, and that you should take care that the insulation is not compromised. Especially: mount the trafo on some insulating material between the chassis and the trafo.
2. 0.3V ripple for phono stage may be too much, but for other applications, it's OK.
If you connect the heater to the dc output though, please remember that the secondary winding of most toroids is the OUTER winding, and that you should take care that the insulation is not compromised. Especially: mount the trafo on some insulating material between the chassis and the trafo.
2. 0.3V ripple for phono stage may be too much, but for other applications, it's OK.
Thanks Rod. 
1. My initial plan was to use a 15V toroid to power them in series (12.6V), and use a high powered 2.4 ohms resistor to reduce the voltage (I am not even sure if I can assume the heater as a fixed resistive load). If it is as you said I guess I would just use a larger toroid and risk it. The rectifier tube is is feeding a 20mA supply, which I guess is on the low side.
2. It is for a "spud" headphone amplifier which tend to be more sensitive than say a pre amp.
1. My initial plan was to use a 15V toroid to power them in series (12.6V), and use a high powered 2.4 ohms resistor to reduce the voltage (I am not even sure if I can assume the heater as a fixed resistive load). If it is as you said I guess I would just use a larger toroid and risk it. The rectifier tube is is feeding a 20mA supply, which I guess is on the low side.
2. It is for a "spud" headphone amplifier which tend to be more sensitive than say a pre amp.
The heater load will be different COLD than HOT but once HOT it is pretty constant.
Why not use an LM317 and regulate the heater supply. You could even use it in CCS configuration which will give the valves a degree of safety against heater element failure.
You only need a Bridge Rectifier, a relatively small cap 2200uF or so, the LM317 and a few resistors.
Why not use an LM317 and regulate the heater supply. You could even use it in CCS configuration which will give the valves a degree of safety against heater element failure.
You only need a Bridge Rectifier, a relatively small cap 2200uF or so, the LM317 and a few resistors.
I am open to all suggestions actually, given how little I know. Initially my plan was to use commercially available board kits, like this:
H-PS-1 low-voltage regulator
But it is out of stock now. I tried to look for alternatives, or schematic that is not too complicated, but have not found any. So I took the easy way out.
Basically I need 850mA at 6.3V per tube. A brief search finds me this:
LM317 High Current Voltage Regulator - Electric Circuit
Please point me to a schematic if you have any.
H-PS-1 low-voltage regulator
But it is out of stock now. I tried to look for alternatives, or schematic that is not too complicated, but have not found any. So I took the easy way out.
Basically I need 850mA at 6.3V per tube. A brief search finds me this:
LM317 High Current Voltage Regulator - Electric Circuit
Please point me to a schematic if you have any.
Hi!
6V will be fine for the rectifier, as suggested, if you pick a toroid with a higher current rating than required, the output will be a bit more and closer to 6.3V
I would suggest to try AC on the 6H30 first. If laid out neatly, it should not hum. You could still convert to DC if necessary
Best regards
Thomas
6V will be fine for the rectifier, as suggested, if you pick a toroid with a higher current rating than required, the output will be a bit more and closer to 6.3V
I would suggest to try AC on the 6H30 first. If laid out neatly, it should not hum. You could still convert to DC if necessary
Best regards
Thomas
I am lazy and I kinda like that idea, it's like cutting the gordian knot.
I am looking at this 6V 8A toroid (12V 4A CT), it might just work to supply all 4 tubes (6.3V 3.7A). I never seem to observe my mains go below 230V, which I suppose I should be able to hit 6V which is the lower bracket.
If it hums, I guess I could use the 12V CT and make me a 6.3V DC?
I am looking at this 6V 8A toroid (12V 4A CT), it might just work to supply all 4 tubes (6.3V 3.7A). I never seem to observe my mains go below 230V, which I suppose I should be able to hit 6V which is the lower bracket.
If it hums, I guess I could use the 12V CT and make me a 6.3V DC?
Hi!
I'd keep the heaters of the rectifier and signal tubes separate! Connect the rectifier heater to the rectifier cathode at one point.
Often it is beneficial to bias the heater of signal tubes slightly positive say 20-25V. This is done by connecting one end of the heater to a voltage divider across B+. Connect a cap in parallel to the resistor to ground. This biases the parasitic diode between heater and cathode positive and minimizes leakage
Best regards
Thomas
I'd keep the heaters of the rectifier and signal tubes separate! Connect the rectifier heater to the rectifier cathode at one point.
Often it is beneficial to bias the heater of signal tubes slightly positive say 20-25V. This is done by connecting one end of the heater to a voltage divider across B+. Connect a cap in parallel to the resistor to ground. This biases the parasitic diode between heater and cathode positive and minimizes leakage
Best regards
Thomas
Hi Thomas,
Please pardon me as I know quite little of these stuffs.
For the rectifier tube, may I know what is the purpose of biasing the heater?
As for the signal tube, can you please correct me if I am wrong?
So I wire both ends of the heater to both end of the heater transformer as usual. And only on one end of the heater I have an extra wire that branches out, one end to the B+ supply (with a resistor in series) and another to the ground (with a resistor in series and a capacitor in parallel to the resistor)?
Thanks.
Please pardon me as I know quite little of these stuffs.
For the rectifier tube, may I know what is the purpose of biasing the heater?
As for the signal tube, can you please correct me if I am wrong?
So I wire both ends of the heater to both end of the heater transformer as usual. And only on one end of the heater I have an extra wire that branches out, one end to the B+ supply (with a resistor in series) and another to the ground (with a resistor in series and a capacitor in parallel to the resistor)?
Thanks.
Hi!
It avoids a large voltage difference bewteen heater and cathode. Although the tube is rated for this, it eases stress on the tube
I think you got it ok, just to be sure:
Say you have a 250V B+. Connect two resistors in series from B+ to ground, a 100k and a 10k. The 10k on the ground side. Add a 10uF/40V or higher parallel to the 10k. Connect one end of the heater to the connection point of the two resistors.
Best regards
Thomas
It avoids a large voltage difference bewteen heater and cathode. Although the tube is rated for this, it eases stress on the tube
I think you got it ok, just to be sure:
Say you have a 250V B+. Connect two resistors in series from B+ to ground, a 100k and a 10k. The 10k on the ground side. Add a 10uF/40V or higher parallel to the 10k. Connect one end of the heater to the connection point of the two resistors.
Best regards
Thomas
Another question.
So I got myself a 6-0-6V transformer (12V CT, not dual secondary). When I use one side of the 6V for the amplifier tube heater and bias it wit B+ as said earlier, can I still tie the cathode of the rectifier tube with the heater with the other side of 6V?
Should I not connect the cathode to the heater on the rectifier tube, since both the heater of the amplifier tube and the rectifier tube is connected through the transformer?
Is it even a good idea to share a transformer like that?
Thanks.
So I got myself a 6-0-6V transformer (12V CT, not dual secondary). When I use one side of the 6V for the amplifier tube heater and bias it wit B+ as said earlier, can I still tie the cathode of the rectifier tube with the heater with the other side of 6V?
Should I not connect the cathode to the heater on the rectifier tube, since both the heater of the amplifier tube and the rectifier tube is connected through the transformer?
Is it even a good idea to share a transformer like that?
Thanks.
You are right, if you bridge rectify and filter 6VAC or 6.3VAC you'll end up with 8.4 to 9VDC unloaded. And that will drop as you increase the number of filaments. So it has to be regulated. But the problem with using the LM317 is that it needs at least 1.5V of headroom so it is likely to drop out. And it's limited to 1.5A or so. So using only 6VAC input isn't safe except for low heater currents. I've had good success with the MIC29750-5.0 regulator (digikey has it) and two 1N914 diodes on the reference pin. Since it is a low dropout regulator, it can regulate with only 350mV of headroom, and supply at least 5A. With such a low headroom, you can mount the regulator to the chassis as a simple heatsink (using an insulator).
You guys are not reading the earlier post.
I will be feeding AC to the the heater.
But an unrelated question, supposedly I am feeding DC to the heater, would it still be beneficial to bias the heater?
But please answer my earlier questions.
So I got myself a 6-0-6V transformer (12V CT, not dual secondary). When I use one side of the 6V for the amplifier tube heater and bias it wit B+ as said earlier, can I still tie the cathode of the rectifier tube with the heater with the other side of 6V?
Should I not connect the cathode to the heater on the rectifier tube, since both the heater of the amplifier tube and the rectifier tube is connected through the transformer?
Is it even a good idea to share a transformer like that?
Thanks.
I will be feeding AC to the the heater.
But an unrelated question, supposedly I am feeding DC to the heater, would it still be beneficial to bias the heater?
But please answer my earlier questions.
So I got myself a 6-0-6V transformer (12V CT, not dual secondary). When I use one side of the 6V for the amplifier tube heater and bias it wit B+ as said earlier, can I still tie the cathode of the rectifier tube with the heater with the other side of 6V?
Should I not connect the cathode to the heater on the rectifier tube, since both the heater of the amplifier tube and the rectifier tube is connected through the transformer?
Is it even a good idea to share a transformer like that?
Thanks.
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