Power supply delima
I just finished constructing a power supply for a tube amp.
The B+ transformer is 510-0-510 but I am getting 700+ when all I want is around 500V
setup:
transformer > Full Wave > Cap > Choke >Cap
The transformer is a hammond 717 Specs
Is there any way to regulate this simply?
Thanks
Keith
I just finished constructing a power supply for a tube amp.
The B+ transformer is 510-0-510 but I am getting 700+ when all I want is around 500V
setup:
transformer > Full Wave > Cap > Choke >Cap
The transformer is a hammond 717 Specs
Is there any way to regulate this simply?
Thanks
Keith
getting a higher voltage than 500V makes sense, seeing as it's a cap input filter... 510*sqrt(2) = 720. if you wanted better regulation, you could expect around 90% of the voltage, or 460.
Yes I have put a load on it and the voltage is still way to high.
How exactly could I regulate the voltage?
How exactly could I regulate the voltage?
Hi kff322,
Remove the first cap. Provide a minimum load on the supply so the choke does not "drop out". That should do it for you.
-Chris
Remove the first cap. Provide a minimum load on the supply so the choke does not "drop out". That should do it for you.
-Chris
Kff322,
Chris is correct. To get the rail voltage where you want it, you should use a (tweaked) choke I/P filter. What is the value of the choke you are currently using? The critical current draw (in mA.) needed for good regulation is approx. V/L. Please observe that larger inductors require a smaller minimum draw for proper performance.
Are you using SS diodes? If so, protective measures are in order. Inductive "kick back" spikes that are not taken into account can DESTROY SS diodes with HIGH PIV ratings.
Older editions of the ARRL handbook teach that the way to execute a choke I/P filter is LCLC. The 1st inductor takes a BEATING and must be robust. The 2nd inductor can be of "ordinary" construction.
Chris is correct. To get the rail voltage where you want it, you should use a (tweaked) choke I/P filter. What is the value of the choke you are currently using? The critical current draw (in mA.) needed for good regulation is approx. V/L. Please observe that larger inductors require a smaller minimum draw for proper performance.
Are you using SS diodes? If so, protective measures are in order. Inductive "kick back" spikes that are not taken into account can DESTROY SS diodes with HIGH PIV ratings.
Older editions of the ARRL handbook teach that the way to execute a choke I/P filter is LCLC. The 1st inductor takes a BEATING and must be robust. The 2nd inductor can be of "ordinary" construction.
Remember transformer voltage ratings are in RMS which means your rectified DC voltage will be 1.41 x transformer voltage rating. Then subtract (idle current X DC resistance of the choke). The Most common way to reduce voltage in a tube amp is to put a resistor followed by a decoupling cap.
excuse me for this intervention.
on datasheet hammond trasfo i read CCS & ICAS
What does it mean CCS and ICAS ?
tnx !
on datasheet hammond trasfo i read CCS & ICAS
What does it mean CCS and ICAS ?
tnx !
The terms refer to radio transmitters. Amateur (aka ham) radio operators tend to transmit for a few seconds while talking, then the transmitter goes on standby while they listen. Commercial transmitters tend to transmit continuously for hours at a time. The difference is that in the intermittent case the tubes, transformers, whatever will not have a chance to get very hot if they are run hard for only a few seconds at a time.
With a little thought it's not too hard to realize that an audio playback amp is being run more or less continuously, so the ICAS rating is the one to pay attention to.
-- Dave
Kff322,
While your 3 H. choke is hefty, it is inadequate for duty as the 1st inductor in a choke I/P filter. Along with the minimum current draw, there is a minimum inductance requirement. The higher the rail voltage, the larger the 1st inductor must be. 3 H. is insufficient in this application, in the 1st position, but it's OK for the 2nd inductor. You need a 10 H. Hammond 193Q (HEFTY) in the 1st position.
To protect the SS diodes from inductive kick back, a 10 nF. ceramic cap. of the highest WVDC you can obtain connects the tied cathodes to ground. Follow the 10 H. 1st inductor with a 47 muF. 'lytic paralleled by a 50 W./10 KOhm power resistor. The 10 KOhm bleeder insures that the minimum current draw is always present. Follow the initial LC section with the 3 H. choke and pile the capacitance up after the 2nd inductor.
Expect the rail voltage to come in around 450 V. If you need a few more Volts, parallel the 10 nF. safety part with a SMALL (< 1 muF.) amount of additional capacitance. The exact value of the "fudge factor" cap. has to be determined experimentally at the bench.
While your 3 H. choke is hefty, it is inadequate for duty as the 1st inductor in a choke I/P filter. Along with the minimum current draw, there is a minimum inductance requirement. The higher the rail voltage, the larger the 1st inductor must be. 3 H. is insufficient in this application, in the 1st position, but it's OK for the 2nd inductor. You need a 10 H. Hammond 193Q (HEFTY) in the 1st position.
To protect the SS diodes from inductive kick back, a 10 nF. ceramic cap. of the highest WVDC you can obtain connects the tied cathodes to ground. Follow the 10 H. 1st inductor with a 47 muF. 'lytic paralleled by a 50 W./10 KOhm power resistor. The 10 KOhm bleeder insures that the minimum current draw is always present. Follow the initial LC section with the 3 H. choke and pile the capacitance up after the 2nd inductor.
Expect the rail voltage to come in around 450 V. If you need a few more Volts, parallel the 10 nF. safety part with a SMALL (< 1 muF.) amount of additional capacitance. The exact value of the "fudge factor" cap. has to be determined experimentally at the bench.
Thanks Guys
Alrighty thanks a lot guys, I think theres enough info posted here to begin some tinkering.
Because it is hard to support an audiophile budget as a high school student working at Stop & Shop in NJ, I have to make due with the 3H choke and I cant buy a 50Watt resistor. anyways.
Eli Duttman, could you tell me more about minimum inductance requirement?
I think I may end up using a step down transformer or something
Alrighty thanks a lot guys, I think theres enough info posted here to begin some tinkering.
Because it is hard to support an audiophile budget as a high school student working at Stop & Shop in NJ, I have to make due with the 3H choke and I cant buy a 50Watt resistor. anyways.
Eli Duttman, could you tell me more about minimum inductance requirement?
I think I may end up using a step down transformer or something
Kieth,
Keep TANSTAAFL firmly in mind. The Laws of Physics restrict your options. Hammond 700 series power trafos are rated for use with choke I/P filters. If a cap. I/P filter is used, figure on getting about 1/2 the current you'd get with choke I/P filtration.
How much DC current do you really need? Forget about using a cap. I/P filter above 250 mA. with your power trafo. If 250 mA. is enough, we can try to tackle the problem in a less costly fashion than buying that BIG choke.
Critical inductance and critical current are terms relating to choke I/P filtration. You don't worry about them when cap. I/P filtration is employed. An inductor stores energy in a magnetic field. Large inductors store more energy than small inductors. Sufficient energy storage is needed to deal with a given voltage. More energy storage is needed at higher voltages. Assuming the minimum inductance requirement for a particular voltage is met, the critical current = a draw sufficient to result in the rectifier winding conducting 100% of the time. Ignoring the inevitable losses, a choke I/P filter yields a DC voltage = average of the AC voltage. 0.9X RMS is a good approximation.
I leave it for a REAL expert to provide the mathematically rigorous derivation of the rules of thumb we use.
Keep TANSTAAFL firmly in mind. The Laws of Physics restrict your options. Hammond 700 series power trafos are rated for use with choke I/P filters. If a cap. I/P filter is used, figure on getting about 1/2 the current you'd get with choke I/P filtration.
How much DC current do you really need? Forget about using a cap. I/P filter above 250 mA. with your power trafo. If 250 mA. is enough, we can try to tackle the problem in a less costly fashion than buying that BIG choke.
Critical inductance and critical current are terms relating to choke I/P filtration. You don't worry about them when cap. I/P filtration is employed. An inductor stores energy in a magnetic field. Large inductors store more energy than small inductors. Sufficient energy storage is needed to deal with a given voltage. More energy storage is needed at higher voltages. Assuming the minimum inductance requirement for a particular voltage is met, the critical current = a draw sufficient to result in the rectifier winding conducting 100% of the time. Ignoring the inevitable losses, a choke I/P filter yields a DC voltage = average of the AC voltage. 0.9X RMS is a good approximation.
I leave it for a REAL expert to provide the mathematically rigorous derivation of the rules of thumb we use.
The load I need is about 400ma max at ~500VDC as you know the transformer is rated for 500ma. It powers a Harman Kardon Cit II clone specificaly.
I did some more experimenting with various configurations and realized that this needs more work and the lowest I could get the voltage was around 545 with just Power Xforer > Choke > Cap which I know is not a healthy setup. I can order a verity of new parts as long as its not a new choke.
Thanks
BTW - how loud of a hum should the transformer be putting out unloaded?
I did some more experimenting with various configurations and realized that this needs more work and the lowest I could get the voltage was around 545 with just Power Xforer > Choke > Cap which I know is not a healthy setup. I can order a verity of new parts as long as its not a new choke.
Thanks
BTW - how loud of a hum should the transformer be putting out unloaded?
The transformer shouldn't hum at all with or without load... but then it IS a Hammond...
You're on the right track - 3 Henries is enough to regulate - barely. You can increase C if L-C still has too much ripple - you'll need to stack electrolytics - I can send you some 470/400V caps for my cost... postage.
You MUST use choke input to get 400 mA out of this transformer - figure 300 mA with cap input. With solid state diodes add an MOV across the input of the choke to ground, or a diode across the choke to limit inductive kick-back.
You're on the right track - 3 Henries is enough to regulate - barely. You can increase C if L-C still has too much ripple - you'll need to stack electrolytics - I can send you some 470/400V caps for my cost... postage.
You MUST use choke input to get 400 mA out of this transformer - figure 300 mA with cap input. With solid state diodes add an MOV across the input of the choke to ground, or a diode across the choke to limit inductive kick-back.
Kieth,
Tom Bavis' remark about your 3 H. choke being barely adequate for service in the 1st position is good news. You're going to need additional inductance in the 2nd position, but that can be purchased at reasonable cost.
You can't tolerate the loss a critical current bleeder resistor introduces. However, the 400 mA. draw of the amp more than meets the critical current criterion. As long as you sequence events properly, the amp will work well. Power MUST be applied to the bias supply and tube heaters before it is applied to the B+ supply. After sufficient time has passed for the O/P tubes to fully heat up, power is applied to the B+ PSU. Look here for a discussion about sequencing.
Since relatively small inductors are being employed, most of the ripple suppression will have to be done by the filter caps. Make the 1st filter cap. 100 muF. Follow the 1st filter cap. with a pair (1/channel) of Triode Electronics C354 chokes that cost $23. The pseudo dual mono topology improves channel separation. Use equal amounts of capacitance in both channels after the 2nd inductor. A good deal of energy storage is in order after each of the 2nd inductors.
B+ in a Cit. 2 should be about 480 V. You will have to use a "fudge factor" cap. to get that voltage. This is actually good news, since the tweaking capacitance will provide protection for the SS diodes against inductive kick back. Be certain you start with the 10 nF. part previously mentioned in place. That's the down payment on the kick back insurance policy.
Tom Bavis' remark about your 3 H. choke being barely adequate for service in the 1st position is good news. You're going to need additional inductance in the 2nd position, but that can be purchased at reasonable cost.
You can't tolerate the loss a critical current bleeder resistor introduces. However, the 400 mA. draw of the amp more than meets the critical current criterion. As long as you sequence events properly, the amp will work well. Power MUST be applied to the bias supply and tube heaters before it is applied to the B+ supply. After sufficient time has passed for the O/P tubes to fully heat up, power is applied to the B+ PSU. Look here for a discussion about sequencing.
Since relatively small inductors are being employed, most of the ripple suppression will have to be done by the filter caps. Make the 1st filter cap. 100 muF. Follow the 1st filter cap. with a pair (1/channel) of Triode Electronics C354 chokes that cost $23. The pseudo dual mono topology improves channel separation. Use equal amounts of capacitance in both channels after the 2nd inductor. A good deal of energy storage is in order after each of the 2nd inductors.
B+ in a Cit. 2 should be about 480 V. You will have to use a "fudge factor" cap. to get that voltage. This is actually good news, since the tweaking capacitance will provide protection for the SS diodes against inductive kick back. Be certain you start with the 10 nF. part previously mentioned in place. That's the down payment on the kick back insurance policy.
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