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Old 9th May 2011, 01:14 AM   #10601
6L6 is offline 6L6  United States
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Quote:
Originally Posted by merlin2069er View Post
I'm using 5x20mm 2.5A fuses (slow blow) for my F5. I just popped one with my transformer and bridges hooked up into the power supply unit.
I tested each primary side of the transformer to the outputs of each bridge ok.
I might have a short somewhere in the power supply I guess.
The most logical place to start is to make sure that you have each of the primaries connected properly, and then double check that the secondaries are also connected proper.

You should have continuity between the each black and red primaries, and the same on the green/blue secondaries. If you have any wire mis-connected, it will screw up half of the transformer, and pop the fuse.

Photos of your build would be very helpful to assist in troubleshooting.

Here are some pictures of the connections in various builds -

Click the image to open in full size.

Click the image to open in full size.
Note the 'A' and 'B' primaries are the twisted pairs.

Click the image to open in full size.

Click the image to open in full size.
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Old 9th May 2011, 07:30 AM   #10602
Marra is offline Marra  United Kingdom
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Follow Andrew T's guidelines and use a bulb tester it saves a lot of hearache.
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Old 9th May 2011, 07:29 PM   #10603
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Default F5 finished

I finished my F5 today and it is working properly. Adjusted now at 90% of target Iqs for a few days to come and than I will test it again. Sound is already great. I am a happy man!! Thanks Peter Daniel for your pcb's and all your advices, h_a for the matched transistors, Zen Mod's very practical initial testing manual an of course mister Pass for giving us the scheme. Enjoying time started. Here are a few pics.
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File Type: jpg F5_2.jpg (591.7 KB, 406 views)
File Type: jpg F5_3.jpg (497.1 KB, 378 views)
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Old 9th May 2011, 08:00 PM   #10604
NYCOne is offline NYCOne  United States
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Quote:
Originally Posted by Nelson Pass View Post


Who summons the JFET genie?
Can I call the MOSFET genie about cascoding outputs of an F5?
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Old 9th May 2011, 08:15 PM   #10605
Zen Mod is offline Zen Mod  Serbia
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you don't need cascoding outputs on F5

just keep each one in safe area regardng dissipation and - if you need more overall dissipation - double number of outputs

they're more than capable , voltage vise

possible benefits from cascoding are smaller than harm induced by voltage losses
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Old 9th May 2011, 09:11 PM   #10606
NYCOne is offline NYCOne  United States
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Quote:
Originally Posted by Zen Mod View Post
not Mosfet Genie itself but resident Court Jester

you don't need cascoding outputs on F5

just keep each one in safe area regarding dissipation and - if you need more overall dissipation - double number of outputs

they're more than capable , voltage vise

possible benefits from cascoding are smaller than harm induced by voltage losses
You may not have seen my earlier post, I want to use Toshiba 2SK3497/2SJ618 at least in single, and perhaps as multiple outputs. They have a high Ciss. I'd like to cascode in any case. I haven't seen much if anything about cascoding F5 outputs. I could be going down the wrong path, but it seems like cascoding might help in this case.

Do you have any thoughts on cascoding the output Mosfets on the F5, it opens up a lot of possibilities.
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Old 9th May 2011, 09:49 PM   #10607
alazira is offline alazira  United States
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Quote:
Originally Posted by 6L6 View Post

Click the image to open in full size.

The top row red/black wires look to be a half mm from shorting in that picture.
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Old 9th May 2011, 09:52 PM   #10608
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by NYCOne View Post
......

Do you have any thoughts on cascoding the output Mosfets on the F5, it opens up a lot of possibilities.
patent 5343166

fig. 5

use PAT2PDF - Free PDF copies of patents: Download and print!

set cascode to have at least 15V across each gain mosfet

edit - disregard additional current sources across gain mosfets on Fig.5
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Last edited by Zen Mod; 9th May 2011 at 09:59 PM.
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Old 9th May 2011, 10:02 PM   #10609
flg is offline flg  United States
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Yes, cascoding could probably provide the best sound with the transistors your speaking of. The downside is going to be when you figure out how much heat sink and power supply you'll need and how little the power output is. you'll need something like twice the rail voltage. That probably will be twice the power dissapation to get the same output power as a pair of IRFs or Faichilds. They probably work better at higher voltage too!
It's not usually done for those reasons. Having said that, I would say your biggest bang for the buck, is higher bias with more heat sink.
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Old 9th May 2011, 11:19 PM   #10610
NYCOne is offline NYCOne  United States
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Quote:
Originally Posted by flg View Post
Yes, cascoding could probably provide the best sound with the transistors your speaking of. The downside is going to be when you figure out how much heat sink and power supply you'll need and how little the power output is. you'll need something like twice the rail voltage. That probably will be twice the power dissapation to get the same output power as a pair of IRFs or Faichilds. They probably work better at higher voltage too!
It's not usually done for those reasons. Having said that, I would say your biggest bang for the buck, is higher bias with more heat sink.
I guess I'll try them as a drop in replacement to the 2SK1530/2SJ201s and see what happens.
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