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Old 20th June 2006, 05:15 PM   #611
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Default Re: Just curious....

Quote:
Originally posted by quasi
My my Shawn that is a big main heatsink. Concerning the other one (the one that is supported by the transistors only!) how does it feel?
The driver heat sink is good and very light but I’m worried long term vibration and mechanical shock would jeopardize the solder points so I have reconsidered and mounting brackets are a must.

Quote:
Originally posted by quasi
Anyway I go to some length to make sure the 10 FET board can be printed on an A4 page, and what do I discover? .....a mezzanine DC detect board?[/B]
And it breaks your heart There is a few reasons and luck too. I decided when reading the beginning of the thread to build the Quasi amp, then further in reading the 10fet amp came up but I already bought a few parts ie PCB boards. I use presensitized PCBs and the 12 inch boards cost a small fortune$$. The aluminum extrusions will be stacked side by side with the fins vertical for max convection. Two extrusions wide only measures 10-1/4 inches, that’s lucky.

Quote:
Originally posted by quasi
Seriously your construction thus far looks good, let us know when you fire it up. Cheers [/B]
Thank you but I have a few questions first in a post to follow…

Quote:
Originally posted by bigpanda
Hi Shawn,
Just what size of heatsink are we looking at ?
I purchased 4 or 5 of those and it measures 3-1/2” by 5-1/16” by 14” long. The PCBs will be mounted perpendicular to the direction on the fins and the image is just a test set up. Also, in the same purchase there is a bunch of heat sinks of the same extrusion but the length is shorter at 9-1/4 inches long. I have 4 of the smaller ones.

Quote:
Originally posted by quasi
. So is Shawn's amp the first 10 FET version about to be fired up, or have others built it? Cheers
I like the thought of that, is it a race to the finish, do I get a prize…oh yeah, I get a nice amp.

Shawn.
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Old 20th June 2006, 05:21 PM   #612
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Default Initial power up

Set up and test:
Open potentiometers to highest ohm
Replace fuses with 100ohm resistors?
Then what?

Shawn.

P.S. I have a variac, scope and two digital VOMs.
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Old 20th June 2006, 05:30 PM   #613
AndrewT is offline AndrewT  Scotland
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Hi Tom,
plug in your series mains light bulb, it''ll protect the Variac if your amp has a short or serious overload.

I assume you have built one.
It consists of plug top, bulbholder and socket outlet. It can be used for first start up of any mains project.
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regards Andrew T.
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Old 20th June 2006, 05:31 PM   #614
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Default IRFP450 isolation on tab

The data sheet for the International Rectifier IRFP450 says," ...the TO-247 is similar but superior to the earlier TO-218 package because of its isolated mounting hole."

I have seen in various pictures people mounting these FET's with insulated washers? Are these people using a different FET? I tested the conductance from the three leads to the steel portion on the backs of these HEXFETs and there is none.

Can I mount just using grease and a bolt? It all sounds right to me and I would get much better heat dissipation.

Cheers,

Shawn.
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Old 20th June 2006, 07:16 PM   #615
sek is offline sek  Germany
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Hi Shawn,

that's about the mounting hole. The screwhead (there it is again ) rests on top of the plastic device...
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Old 20th June 2006, 08:24 PM   #616
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Default Screwsheads and IRPF450s

Quote:
Originally posted by sek
Hi Shawn,

that's about the mounting hole. The screwhead (there it is again ) rests on top of the plastic device...
The top and the shaft of the through mounting hole have no metal near them. On the back, mounting side, there is a piece of bare metal but it does not make electrical contact with any of the three leads on the device.

Is it safe to mount without insulating washer?

Shawn.

(there it is again) You rock.

P.S. I remember the slang of that expression from the classic DeNiro flick Taxi Driver and of later impression as sampled by The Clash in the lyric from Red Angel Dragnet. Everytime I see it or hear it, trigger...I'm weird.
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Old 20th June 2006, 10:15 PM   #617
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Default Re: IRFP450 isolation on tab

Shawn,

You had my curiousity sparked from your reading and observations of the IRFP450. I took out some IRFP450s and checked them. Sure enough the middle lead, drain, is same as the metal back electrically. In other words the drain lead and metal back are same.

I think the reference the IRFP450 datasheet makes, that you quoted, at start of data sheet is strickly about the mounting hole, which is in fact isolated. The older IRF data sheets, including IRFP450, IRFP240 do not list the case and pinout information on the datasheet, but refer one to a different page that is of course not part of the data sheet.

The IRFP450 information is found at:

http://ec.irf.com/v6/en/US/adirect/i...uctID=IRFP450:

On that page is a link to the package type "TO-247AC" that leads you to:

http://www.irf.com/package/pkhexfet.html

On that page you will find "TO-247AC", "Package Outline"

http://www.irf.com/package/hexfet/to247.pdf

Here you will note that "2" and "4" are both drain, "2" being the pin, an "4" being the "THERMAL PAD" of "VIEW A-A".

This means that you still have to insulate the IRFP450's from the heatsink, notwithstanding the mounting hole is in fact insulated.

I hope this clarifies why you still need to insulate electrically, but thermally couple the IRPF450 to the heatsink or for that matter any TO-247(AC) case stype device.


Regards,

John L. Males
Willowdale, Ontario
Canada
20 June 2006 18:18
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P.S. My appologies in advance for any typo errors. If you cannot "decode" the typo or feel there is a typo (some typos are correctly typed spelling, but can be mix of wrong/omitted words) speak up and ask me to clarify. jlm
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Old 20th June 2006, 10:32 PM   #618
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Default Re: Re: IRFP450 isolation on tab

Quote:
Originally posted by the drooling keypunch
What T8 device did you choose? Enjoy the hockey game
Canadian players win but Canadian teams can not and what is up with the Losers, I mean Leafs? Ha Ha its all over.

I will be using the external T8 in the actual power amp but for testing I am in the hole.

Quote:
Originally posted by keypunch This means that you still have to insulate the IRFP450's from the heatsink...[/B]
I appologise everybody, the back tab shares the drain. I did the measurements last night !!! As you were. Thanks John.

Again whats the set up procedure and measurements to set the two pots?

Shawn.
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Old 20th June 2006, 11:44 PM   #619
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Quote:
Originally posted by jacco vermeulen


Care to give the title ?

(Quasi, whip Guuseroo for the Croatia/Hrvatska thingy)
Hi Jacco,

Here is the information for the book:

Thomas L. Floyd

ELECTRONICS FUNDAMENTALS: CURCUITS, DEVICES AND APPLICATIONS


Merrill Publishing Company
A Bell & Howell Information Company
Columbus Toronto London Melbourne

Published by
Merrill Publishing Company
A Bell & Howell Information Company
Columbus, Ohio 43216


Copyright 1987

Library of Congress Catalog Number: 86-61567
International Standard Book Number: 0-675-20714-2
Published in the United States of America
4 5 6 7 8 9-91 90 89


Regards,

John L. Males
Willowdale, Ontario
Canada
20 June 2006 19:46
20 June 2006 20:13 Removed stray quote jlm
__________________
P.S. My appologies in advance for any typo errors. If you cannot "decode" the typo or feel there is a typo (some typos are correctly typed spelling, but can be mix of wrong/omitted words) speak up and ask me to clarify. jlm
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Old 21st June 2006, 12:09 AM   #620
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Hi Shawn,

I was aware you would use an "external" T8, and it would be a TO-126 device. I was curious what you were going to use, as in a BD139, etc?

Have you fired up either of the modules yet? Even tried to play music through after the initial Vbe bias setup?


Regards,

John L. Males
Willowdale, Ontario
Canada
20 June 2006 20:12
__________________
P.S. My appologies in advance for any typo errors. If you cannot "decode" the typo or feel there is a typo (some typos are correctly typed spelling, but can be mix of wrong/omitted words) speak up and ask me to clarify. jlm
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