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Old 28th September 2003, 01:39 PM   #11
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Hi,

Quote:
It would reduce switching transcients and reduce noise presumably...
In the hybrid rectifier as shown there is NO switching noise so a simple pair of 1N4007 would do just fine.

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Old 28th September 2003, 01:57 PM   #12
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Yeah...I thought he was referring to other all SS rectifier applications...for the tube application...I guess you will just use whatever you have in hand...
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Old 28th September 2003, 03:06 PM   #13
Raj1 is offline Raj1  United Kingdom
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Hi everyone,

The transformer I have is rated at 120va.

Another silly question for you all

in ultranalog's schematic, he's attatched pins 3 & 4 to B+.

But in the diagram shown in the az1 pinout data only pin 3 is connected to B+.

I've tried the rectifier like in the data sheet with only pin 3 connected accross 1 of the 47 ohm resistors, I'm getting 175 volts at this point.


So should pin 2 be connected also???

Or should I just be using pin 3, and the 47 ohm resistors in parrallel?

Thanks
Raja
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Old 28th September 2003, 03:15 PM   #14
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Hi,

To the best of my knowledge there's nothing connected to pins #s

1, 4, 6 and 7.

Pin # 2 & 3 are the heaters (cathode)

Pins 5 & 8 are the anode connections.

Keep in mind that this a directly heated full wave rectifier.

Cheers,
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Old 28th September 2003, 03:36 PM   #15
Raj1 is offline Raj1  United Kingdom
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Hi Fdegrove,

Should I connect like this,
http://www.diyaudio.com/forums/attac...&postid=232367
only pin 3 to B+



or this?
http://www.ultranalog.com/cdenhancer...ancer2_3a5.pdf
both pins 2 & 3 to B+

Sorry if I'm getting confused here, ultranalog's schematic just looks a bit different to the datasheet................

IN any case it looks as if I'm getting to much volatge on B+ it's reading 175 volts after the 680 ohm resistor.

The max for the 3a5's is 135 volts. How come it's so high?

I measured 130v accross the secondries with my dmm. Antrim does state that the reading will be higher than the stated 120v in off load conditions, but I figured it wouldn't be over by this much...

Luckily I havn't yet connected the 3a5's to the circuit.

The choke has a stated dc resitence of 150 ohms.

Can I drop the voltage to a safe margin with another resistor after the 680 ohm res?

Thanks
Raja
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Old 28th September 2003, 03:56 PM   #16
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Hi,

Quote:
both pins 2 & 3 to B+
I don't see that in the PDF file you link to but nevermind...

2 and 3 are connected to the heater supply and the output is behind the 2 resistors. That's your B+.

Either way will work but you'll probably have a little too much voltage.

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Old 28th September 2003, 04:32 PM   #17
Raj1 is offline Raj1  United Kingdom
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Default Too much voltage

The az1's glowing nicely.........

Yep you're right, either way I get 170v after the 680ohm resistor at the end of the circuit.

I doubt whether the total of 14ma drawn by the 3a5's is going to cause 'major sag' on the rail.

1) How many volts can I expect the rail to drop once the 3a5's are connected?

2) So how can I work out how much more resistence I need to get the right voltage at the output?

3) Why has the voltage risen by so much, I thought tube rec's dropped around 15v, and yet here I am with more voltage at B+ than at the secondries....?

Thanks
Raja
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Old 28th September 2003, 05:31 PM   #18
Raj1 is offline Raj1  United Kingdom
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Default dropping voltage

Hi,

Have I worked this out right???


R=V/I

R=110/0.014

R=7857 ohms

7K 857 ohms?????


So if I subtract from 7857, the total value of resistence in the circuit, I should get the value I of resistor I need to drop the voltage???

By the way using my dmm I checked the resistence on the choke pins, which read 270 ohms.

so 680+270+47= 997

7857-997= 6860

I do realise my questions must be irratating guys, but I'm learning, and I do apologise for taking up so much of everyone's time......


Thanks
Raja
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Old 28th September 2003, 05:35 PM   #19
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Hi,

QQ 1 & 2 Ohms law allows for the calculation of that.

Don't work on circuits without a load attached, use a lightbulb or a 15W 470K resistor or similar.

Q 3 I did tell you to remember you're working with a full wave rectifier, hence the higher rectified B+.

Cheers,

Edit: Just noticed your latest post: yes, 7000 ohms = 7K.
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Old 28th September 2003, 05:43 PM   #20
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Hi,

Quote:
7857-997= 6860
Don't forget the internal resistance of the 3A5s as well.

Easiest way to go about it is to build the circuit, check it for short, put the valves in place, than measure the B+ after a few minutes warm up.

See how much voltage you need to drop and using Ohms' magic adjust the dropping resistors.

Always check that the circuit is fully discharged befor putting a hand in it.

Cheers,
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