Hi,
I'm going to power a tube with a heater current rating of 0.8 A, 6.3V.
The transformer I am considering has a secondary current rating of 2A no CT.
I plan to use a bridge rectifier and RC filter to produce DC at 6.3V.
Will the 2A 6.3 VDC transformer be sufficent to power the filament?
I have seen somewhere that the transformer current rating should be 1.8 times the load current when using a bridge.
I normally use a full wave for filaments but no CT in this case.
I'm going to power a tube with a heater current rating of 0.8 A, 6.3V.
The transformer I am considering has a secondary current rating of 2A no CT.
I plan to use a bridge rectifier and RC filter to produce DC at 6.3V.
Will the 2A 6.3 VDC transformer be sufficent to power the filament?
I have seen somewhere that the transformer current rating should be 1.8 times the load current when using a bridge.
I normally use a full wave for filaments but no CT in this case.
IIRC the factor is 1.4. But you have current excess by over two, so you're good. Are you going to regulate the DC to the filament? It is hard to get regulated 6.3vdc from a 6.3vac winding. You will have to use Schottky Diodes and lots of capacitance. The DC to the filament will have to be well filtered (or regulated) or it will cause hum also. Sometimes worse than ac on the filaments.
Good luck...Daniel
PS. I just thought of something else, which I have done with good results, but your transformer may not have enough current output. What I am talking about is configure the transformer as a voltage doubler. Use 2 Diodes and 2 capacitors over 10,000uf each. This will give you around 12-14 volts DC which can be regulated easily as there is enough voltage.
Good luck...Daniel
PS. I just thought of something else, which I have done with good results, but your transformer may not have enough current output. What I am talking about is configure the transformer as a voltage doubler. Use 2 Diodes and 2 capacitors over 10,000uf each. This will give you around 12-14 volts DC which can be regulated easily as there is enough voltage.
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Hi, 1.8 x 0.8A =1.44 times.
2A divide by 0.8A =2.5 times. Theory =1.8? More than adequate even if
power loss is incuded.😀 That's for one tube,if it's for two tubes it will get hot.
So double up if that's the case to run cool. (2 tubes,1.6A X1.8 =2.88) singa
2A divide by 0.8A =2.5 times. Theory =1.8? More than adequate even if
power loss is incuded.😀 That's for one tube,if it's for two tubes it will get hot.
So double up if that's the case to run cool. (2 tubes,1.6A X1.8 =2.88) singa
Thanks,
I plan to run one tube on this supply.
I may try a regulator when the transformers arrive but I'm not sure if I can get enough voltage as I only have 6.3 to start with.
I had not considered the doubler but it is a possibility as well.
I plan to run one tube on this supply.
I may try a regulator when the transformers arrive but I'm not sure if I can get enough voltage as I only have 6.3 to start with.
I had not considered the doubler but it is a possibility as well.
Hi again,
Look at the LT1084, LT1085, LT1086 regulators from Linear Technology. They have low dropout voltage and if you use the above diodes I mentioned with LOTS of capacitance you should be able to pull off regulation.
Daniel
Look at the LT1084, LT1085, LT1086 regulators from Linear Technology. They have low dropout voltage and if you use the above diodes I mentioned with LOTS of capacitance you should be able to pull off regulation.
Daniel
Having so little headroom has bothered me to the point where I changed the transformer design.
I'll go with 8V@ 4 Amps so I will be certain to have enough power to overcome the losses incurred in rectification and regulation and I can run a second tube if needed.
I was going to go with a 6BM8 mu follower to drive my SET output but now I may go with 6SL7 - 6SN7 in the Aikido configuration.
My mistake was in trying to economize on cost, size and weight of the final product.
I'll go with 8V@ 4 Amps so I will be certain to have enough power to overcome the losses incurred in rectification and regulation and I can run a second tube if needed.
I was going to go with a 6BM8 mu follower to drive my SET output but now I may go with 6SL7 - 6SN7 in the Aikido configuration.
My mistake was in trying to economize on cost, size and weight of the final product.
I personally bought a switch mode power supply with adjustable output and called it a day(cost me $20),otherwise I was going to build one custom. Smps are more stable and 80% or better efficient
If you are working on the cheap and only need power for one or two heaters, you can usually find a suitable wall wart at the goodwill for a dollar. Take a DMM with you because you will likely find that half of them are shot. You may want to use a 6 or 12 volt regulator with it.
Hello,
In my playing with stuff I have found that 6.3 Volt transformers with full 4 diode bridge rectifiers do not put out 6.3 volts DC let alone have any voltage to spare for a regulator. 12.6 volt AC transformers with a CT can use a 2 diode full wave rectifiers and work ok. The voltage drop across two diodes in series in the bridge rectifier consumes too much voltage.
The transformers that I like with the full bridge rectifier are 8 volt AC. The 8 volt AC through the diodes and capacitors puts out ~ 9 volts. 9 volts raw DC works well with the 1085 low drop out regulators.
Rule of thumb, I select a transformer with a VA rating at least twice the watts used by the connected heaters. This way the transformer does not get real hot and the voltage does not dip too low.
DT
All just for fun!
In my playing with stuff I have found that 6.3 Volt transformers with full 4 diode bridge rectifiers do not put out 6.3 volts DC let alone have any voltage to spare for a regulator. 12.6 volt AC transformers with a CT can use a 2 diode full wave rectifiers and work ok. The voltage drop across two diodes in series in the bridge rectifier consumes too much voltage.
The transformers that I like with the full bridge rectifier are 8 volt AC. The 8 volt AC through the diodes and capacitors puts out ~ 9 volts. 9 volts raw DC works well with the 1085 low drop out regulators.
Rule of thumb, I select a transformer with a VA rating at least twice the watts used by the connected heaters. This way the transformer does not get real hot and the voltage does not dip too low.
DT
All just for fun!
Theres also the fact that heaters consume a lot on power on. My amplifiers 12.6v supply needed to handle 8 to 10 amps for first two seconds and then 4.5 amps or so thereafter.
Hello,
The internal impedance of the transformer and the charging of the capacitors provides a soft start of sorts for the heaters. You may also consider adding a GE Sensing inrush limiter in the transformer primary to further soften the power inrush in the tube heaters.The transformer has plenty of mass to soak up the heat, the heaters do not. It is about thermal shock.
DT
All just for fun!
Hello, still anyone here ?
I want to use a LT1083 regulator unit to feed 4 tubes.Max power is 3,25 ma.
The LT unit have:
• a 4700uf capacitor at the entrance.
•4 rectifiers bridge
Capacitor's impédance at 100hz is 0,33 Ohms.
I think a 220v/9v ac could be fine.
Max DC voltage is 13,3v.
So the max call current at start is 41 A !
How to size the transformer's power ,please ?
Is there a rule of thumb ?
Regards
I want to use a LT1083 regulator unit to feed 4 tubes.Max power is 3,25 ma.
The LT unit have:
• a 4700uf capacitor at the entrance.
•4 rectifiers bridge
Capacitor's impédance at 100hz is 0,33 Ohms.
I think a 220v/9v ac could be fine.
Max DC voltage is 13,3v.
So the max call current at start is 41 A !
How to size the transformer's power ,please ?
Is there a rule of thumb ?
Regards
It's not impossible. You need at least 1V of compliance and you'll have to work backwards to ensure that regardless of what your powerline voltage is, that 1V will always be there. So if your incoming AC voltage is 220V to 240V, you need to design your raw DC supply to have 1V of compliance with 220V of line voltage.
9V AC bridge rectified into a big capacitor will give you about ~7.75V-9V (I don't count the peaks of the rectified waveform). You'll need a winding rated for 6A for this. Using Schottky diodes will give you more available DC voltage, but you'll need to be mindful of how much current you're drawing through them and how hot they get. Very few TO-220 Schottky diodes will tolerate that kind of draw without a heatsink. If you use a chassis mount bridge rectifier, you'll have a more convenient place to dump the heat but you'll also lose valuable compliance.
Which package of 1083 are you planning to use? They will get quite hot with this kind of current demand.
9V AC bridge rectified into a big capacitor will give you about ~7.75V-9V (I don't count the peaks of the rectified waveform). You'll need a winding rated for 6A for this. Using Schottky diodes will give you more available DC voltage, but you'll need to be mindful of how much current you're drawing through them and how hot they get. Very few TO-220 Schottky diodes will tolerate that kind of draw without a heatsink. If you use a chassis mount bridge rectifier, you'll have a more convenient place to dump the heat but you'll also lose valuable compliance.
Which package of 1083 are you planning to use? They will get quite hot with this kind of current demand.
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Thanks a lot for your reply.
I will choose à 80w 220v/9v transformer, it will bé safe.
The voltage regulator,less than 10$, 4700uf.
For the power dissipation i have calculated 13,5w without voltage drop due to rectifier.
LT1083 Adjustable HIFI Line Regulated Power Supply Module One Channel Output 665230857154 | eBay
I will choose à 80w 220v/9v transformer, it will bé safe.
The voltage regulator,less than 10$, 4700uf.
For the power dissipation i have calculated 13,5w without voltage drop due to rectifier.
LT1083 Adjustable HIFI Line Regulated Power Supply Module One Channel Output 665230857154 | eBay
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I would not buy anything like that from AliExpress or eBay. The Chinese are notorious for making poor copies of expensive voltage regulators.
13.5W of dissipation is tons. I wouldn't put more than 2W into the heatsink on the board you linked to.
13.5W of dissipation is tons. I wouldn't put more than 2W into the heatsink on the board you linked to.