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Old 9th April 2012, 02:13 AM   #12171
Rixsta is offline Rixsta  United Kingdom
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I have put the Thermistors very close to the mosfets, when i hold my finger on the mosfets the temp goes from luke warm to scortching within 20 - 40 seconds then slowly go back to warm, then over again.
when the thermistors are half inch away from the mosfet, the heating and cooling effect speeds up, bias goes up (presume that part is natural)
Is this normal ?
I have Mica Pads and thermal Grease on, and currently biased at .30v instead of .58v as im slowly working my way towards that value.

Last edited by Rixsta; 9th April 2012 at 02:19 AM.
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Old 9th April 2012, 02:43 AM   #12172
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43 degrees on the mosfet
34 degrees on the heatsink
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Old 9th April 2012, 11:25 AM   #12173
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does anyone know to get some nice psu boards? it would be awesome if diy audio store could sell some psu boards that match all those nice boards that the store sells.
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Old 9th April 2012, 01:07 PM   #12174
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Quote:
Originally Posted by Rixsta View Post
I have put the Thermistors very close to the mosfets, when i hold my finger on the mosfets the temp goes from luke warm to scortching within 20 - 40 seconds then slowly go back to warm, then over again.
when the thermistors are half inch away from the mosfet, the heating and cooling effect speeds up, bias goes up (presume that part is natural)
Is this normal ?
.
Yes all normal >thermistor change themperature >resistance change > bias >change >mosfet change temperature >thermistor change themperature >resistance change > bias >change >mosfet change temperature >thermistor change themperature >resistance change > bias >change >mosfet change temperature...

I glue them to drain leg of the mosfet right close to body, that is the hottest place apart from mosfet back metal tagg.
Being hot place and glued on no mather how hard I wave my fingher or shout at the thermistor the temperature wont change much (bead of epoxi resin around it isolating some from ambient)

Surround the thermistor with air and you can sing at it causing bias change.

Obwiously if you know better you are free to do as you like (not going in to this argument again)
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Old 9th April 2012, 02:17 PM   #12175
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Quote:
Originally Posted by TjongKristian View Post
does anyone know to get some nice psu boards? it would be awesome if diy audio store could sell some psu boards that match all those nice boards that the store sells.
There are 2 convenient options -

Peter Daniel's 'Universal' Power supply board from Audiosector.com (Contact Peter through his website, this board is not listed)

Click the image to open in full size.

This uses diode bridges that are not attached to the board. More information in this thread - Universal Power Supply PCB

And the 'Aleph PSU' board from chipamp.com --

Click the image to open in full size.

This has a single bridge that uses TO-220 diodes. It also has room for more filter capacitors.
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Old 9th April 2012, 02:42 PM   #12176
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Quote:
Originally Posted by Bksabath View Post
Yes all normal >
I glue them to drain leg of the mosfet right close to body, that is the hottest place apart from mosfet back metal tagg.
Being hot place and glued on no mather how hard I wave my fingher or shout at the thermistor the temperature wont change much (bead of epoxi resin around it isolating some from ambient)

Surround the thermistor with air and you can sing at it causing bias change.

Obwiously if you know better you are free to do as you like (not going in to this argument again)
Haha Cheers, good to know im a singer but ill be singing outside the chassis

Those PSU baords look great!
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Old 9th April 2012, 02:48 PM   #12177
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Thank you for the info. I do have Brian's PSU board but I am going to use it for my "almost done miniA that has been built for the last 3 years or so." Also, I really prefer the same "design and color" for the psu board.
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Old 9th April 2012, 03:10 PM   #12178
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Quote:
Originally Posted by fdlsys View Post
- as little of thermal paste as possible; basically, so thin that it's almost completely transparent
I made the mistake of adding too much thinking its better, you only need to fill the air gaps i see now about to take a bit off, also i read here at Rod Elliot ESP that with the mica pads u can often split them with a small knife

"So much for the descriptions, but why would mica get a section all of its own? Simply because the quality control is virtually non-existent (from what I have seen lately). The overall shape is fine, but the thickness is generally too great - commonly by a huge margin. I have used mica washers that were so thick that I was able to separate them with a (very) sharp knife, and obtained four washers for the price of one (plus some scrap from the splitting operation). "

Worked Wonders! so im going to try that and find out if the thermals are better or worse, actualy i seperated one with my finger nail haha

Last edited by Rixsta; 9th April 2012 at 03:12 PM.
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Old 9th April 2012, 04:44 PM   #12179
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The answer is..... A Lot cooler Mosfets! a lot thinner Mica
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Old 10th April 2012, 09:45 AM   #12180
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Can I make a F5 with less power if I use a smaller power supply?
What is the smallest Voltage which the F5 can use without loosing quality?
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