Cap size for Aikido heater PS? - diyAudio
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Old 13th October 2007, 06:00 PM   #1
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Default Cap size for Aikido heater PS?

I need some help. I've attached the drawing for the power supply I'm using in my Aikido preamp. My question is do I need to increase the voltage rating of the caps in the heater supply due to the bias voltage from the B+. The bias voltage will be 75 Volts and the caps are only rated at 25 volts, I'm using a transfomer with 290V and running the output of the B+ which should be 340V though a regulator which should drop the B+ voltage down to 300V. In the heater supply to obtain the bias voltage I replaced the value of R6 with a 100K resistor and paralleled a small cap with it and then bridged the two with a 300K resistor and attached the 300K resistor to the regulated B+ 300V. I want to make sure I'm on the right track before I fire this thing up today.

Thanks
Steve
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Old 13th October 2007, 09:27 PM   #2
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Does bias votlage actually increse the voltage of the circuit?
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Old 14th October 2007, 02:31 AM   #3
jnb is offline jnb  Australia
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Respect for HT is a good thing. In this case you are wanting 12V across the caps and that is what the (properly working) circuit will present. Floating the heater by connecting it at just one place to the HT will not put a higher voltage across the capacitor. If it did, your heaters would complain!

Two things you may want to keep in mind. Firstly it makes sense to me to keep the cans physically isolated from other parts of the circuit. Secondly, except that you are using regulators which may make this moot, it is better to use larger caps to handle the ripple from a heater supply.
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Old 15th October 2007, 11:36 AM   #4
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jnb

Thank you much for the reply. That helps!
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Old 15th October 2007, 10:51 PM   #5
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I tested the PS today and all worked. Well I got the desired voltage but R1 got really hot and started to smoke. I shut it down right away. But I don't understand why it got so hot. Does the PS need to under load when tested? How do I make sure I didn't damage R1?
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Old 15th October 2007, 11:08 PM   #6
jnb is offline jnb  Australia
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If it smoked, you could pull it and measure it but I'd preferrably replace it.

In order to dissipate 3W, R1 would have needed more than 50mA. In your case it could have been much more. You say you don't have the pre connected? Perhaps you need to go back and check your board, especially for solder bridges.

There don't seem to be any components that would draw that much current if a fault arose unless you were supplied the wrong values or they have failed short.
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Old 15th October 2007, 11:55 PM   #7
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Thanks jnb, I think the problem lies in the regulator after it, and that just a guess. I wasn't 100% sure of connection when I was building it. I measured R1 in place is that the wrong way to do it? The value seemed ok?
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Old 15th October 2007, 11:57 PM   #8
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Oh and the preamp wasn't attached. Thank you again.
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Old 16th October 2007, 02:26 AM   #9
jnb is offline jnb  Australia
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Quote:
Originally posted by Steve Fay
I measured R1 in place is that the wrong way to do it? The value seemed ok?
In this case it should be OK. You could lift the choke to see that you have 440VDC across the first caps (discharge them through a resistance before proceeding). Anything less might indicate a problem with the caps, wiring or other.

The only devices that would load the circuit, apart from an accidental short circuit, are the caps (if faulty), the zeners and the 150k resistor.

The next thing I'd check is whether the zeners are in backward as they'd then be close to a short to ground and this could have stressed the transistors.


Edit: Vis-a-vis my first suggestion, I just noticed C2 is rated at 400V in the schematic. Though this should be OK under normal use (when loaded), my personal preference would be to increase the voltage rating if for no other reason than that it would be exceeded under a no load condition, should something go wrong. Small caps in HT circuits tend to sound like a .22 calibre round when pushed too far.
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Old 16th October 2007, 01:11 PM   #10
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jnb,
Thanks again for your help! I did increase C2 to a 600v cap before I assembeled the board. I'm going to replace the 150K resistor because it measures 0.642k. I did use Cree CSDO4060 for D1, D2 and D3. I've used them before with good results. I have them in a TO-220 pkg and pin 1 should be the blocking pin. If I'm correct the orinetation is correct. The caps check out ok. I have attached a drawing of the regulator that this PS board feeds. I've attached the B+ and the ground of my power supply to this regulator which I got off John Broski's site. Then attached the ground coming out of the regulator to the case. The only part of the regulator that I question is the pin connections on the IXCY10M45S. I attached the + pin to the + rail and the - pin to the - rail and the gate to the 0.1 cap and the1M resistor as shown in the drawing. I'm not 100% sure if this is correct? I also concerned that this could be the source of the feedback into the power supply? HELP???

Thank you
Steve
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