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F5 Turbo is posted
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Old 31st March 2014, 09:25 AM   #621
AndrewT is offline AndrewT  Scotland
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the current in the upper half is the same as the current in the lower half, because the load is disconnected.

If you are reading 470mVrs and 430mVrs, then there is something wrong with your methodology, the currents cannot be different.

Did you select your Source Resistors?
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Old 31st March 2014, 11:50 PM   #622
Omid is offline Omid  Canada
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I 'm measuring the voltage across the 1 ohm resistors. I have a few digital meters so I'm measuring the N and P sides at the same time. I have shorted the input, but I have also (and I guess that's where the problem is, based on your post) strapped an 8 ohms 20 W resistor across the speaker output terminals. Do you think think that's the issue?
I'll take it off when I get home and retest my voltages.
Thanks for the input AndrewT.
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Old 31st March 2014, 11:55 PM   #623
6L6 is offline 6L6  United States
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F5 Turbo is posted
If you are reading zero DC offset then you will be OK.

I set the bias with no load attached. That may be the culprit, however you mention that your Mosfets are unmatched, you may be reading across one that is current hogging.

Also you mention that your Mosfet are at 75C. Reduce bias until they are stable at 65C.
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Old 1st April 2014, 02:03 AM   #624
Omid is offline Omid  Canada
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Thanks. I measured the voltages without a load. It made no difference. Then rather than always measuring the same Mosfet on each rail (TP 3 and 4 on the PCB bought from this site), I measured the other Mosfet's current, to check for a current hog as you suggested.

You were right, because they're unmatched, one Mosfet draws more current than the other. I expect the sum of the currents on the N side equals the sum on the P side. I guess I should match them if I don't want one Mosfet to get way hotter than the rest. (I'll measure the temp, if it's not different I might to just forget about it).

As an interesting aside, as I'd turned the bias pretty high up, and the diodes hadn't kicked in, I was beginning to wonder if they ever would...They eventually did in spectacular fashion: As I was trouble shooting my bias problem, I decided to add a 3 W 10 Ohms to the 1 ohm resistors on the N side. It did correct the bias problem in the right direction. In the various changes I was making, I once had the bias turned too high, and the variac turned all the way up when I flicked it on. The 10 Ohm resistor burst into flames ! No wonder the manual says you may want to have a fire extinguisher! Luckily nothing else was affected, so all's good.

Last edited by Omid; 1st April 2014 at 02:04 AM. Reason: mistyped
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Old 1st April 2014, 02:32 AM   #625
6L6 is offline 6L6  United States
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F5 Turbo is posted
I believe you are now in the "Fearless Amplifier Builder's Club."

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Old 1st April 2014, 05:01 AM   #626
Omid is offline Omid  Canada
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Yep, almost made it in the hairless amplifier builder's club!
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Old 1st April 2014, 10:54 AM   #627
AndrewT is offline AndrewT  Scotland
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Default setting up F5

The input must be fitted with a dummy load. This ensures there is NO DC voltage applied to the input.
The output load MUST be disconnected.
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Old 4th April 2014, 12:18 PM   #628
Erlend Sæterdal is offline Erlend Sæterdal  Denmark
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F5 Turbo is posted
Default Power Supply PCB

Hi does anybody know where to buy pcb for 16 x 10000 uf 50 V 30 mm Ø ? Just bought 32 ROE 105 celcius from Vilnius .
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Old 4th April 2014, 12:41 PM   #629
AndrewT is offline AndrewT  Scotland
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Bolt or glue the capacitors to the chassis.
Hard wire the pins.
Ensure the loop areas of the hard wiring are minimised.

I use clear silicone window sealer as a glue.
Sometimes to the floor of the chassis, sometimes to the side panel, even to the back panel, if that suits the layout of the other components.
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Old 4th April 2014, 12:46 PM   #630
Erlend Sæterdal is offline Erlend Sæterdal  Denmark
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F5 Turbo is posted
Quote:
Originally Posted by AndrewT View Post
Bolt or glue the capacitors to the chassis.
Hard wire the pins.
Ensure the loop areas of the hard wiring are minimised.

I use clear silicone window sealer as a glue.
Sometimes to the floor of the chassis, sometimes to the side panel, even to the back panel, if that suits the layout of the other components.
Hehe Andrew thats what I usally do. Wanted it to look more professionel this time.
Another thing is I wonder why it use those CRC. 0,07 ohm does not improve anything in my world ?
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