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Old 29th August 2012, 02:02 AM   #3141
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Hi, better measure the consumption of the unit when playing signal, then just add 20mA to that number and set the ccs there. If its really 72mA you need 92mA ccs for example. 1 Ohm in series with its now B+ can let you know the draw by I=Vrdrop/1R in Amps.
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Old 29th August 2012, 02:25 AM   #3142
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OK. I'll give that a shot (still need to build it though !).
So more shunt current isn't necessarily better, or is it more to limit the power dissipation ?
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Old 29th August 2012, 02:36 AM   #3143
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20mA surplus is good to feed own reg needs and keep output impedance low enough. More produces heat fast on the sink due to there is high voltage involved, and in your case when approaching 100mA+ at some point soon you are going to meet the Supertex depletion MOSFET's current generation limit. It is called IDSS and is not the same in each production sample.
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Old 29th August 2012, 02:41 AM   #3144
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You will judge your sinking, given the limit your trimmer will allow along with the MOSFET. If you will afford a bit more surplus current, it does good.
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Old 1st September 2012, 11:13 AM   #3145
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Default SSHV1 BJT version?

Hi,

is it possible to change IRF9610 and IRF840 mosfets for BJTs? If so, any tips on good substitute types?

Thanks.
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Old 1st September 2012, 03:00 PM   #3146
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No good tips because never tried it.
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Old 17th September 2012, 07:52 PM   #3147
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Hi,

I am sure questions like this get covered a lot, so please direct me to the post if you can.

I have my power supply feeding 135V my SSHVII board which is just sitting on my table, which then feeds my #26 preamp in a seperate chassis.

I went through the power on steps - read about 25mA at the test points.

Connected to my preamp, still reading steady current but no HT. It was about 3V.

There is some kind of interference because when I place a meter probe on the test points the LED cuts out, this also happens when I touch the heat sinks - even though these are definitely isolated from the board. Is this a grounding issue? Or maybe a blown device?

Does this sound common? I am checking over everything again and again because 9/10 it's wiring issue with me, but I thought I would ask too.

Thanks

Charlie
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Old 17th September 2012, 08:04 PM   #3148
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Did you check with dummy load first, was it working OK for setting the voltage also? Are the 4 wires to load routed as per instruction sheet?
One thing to know is to have set sufficient ccs current. Try 35mA for two #26 channels because the reg itself will need +20mA on top of those. Then it is going to need 10V minimum input to output difference, 20V is recommended. Is that preamp set for only 105V B+?
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Old 17th September 2012, 08:08 PM   #3149
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What are the consumption and B+ requirements for your preamp per channel?
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Old 17th September 2012, 09:06 PM   #3150
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I followed the instructions for the wiring, and it was working OK with the dummy load.

Consumption for per channel is 6mA plus 20mA across the reg as you said. I do think now that I may be too conservative with my voltage margains - I am aiming for about 105V for the #26, but maybe I need to up the input HT...

It seemed curious that by placing the probe on the board it gave different readings and made the LED shine. Is the LED meant to shine constantly?

Cheers

Charlie
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Last edited by Brouilly; 17th September 2012 at 09:13 PM. Reason: stupid question
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