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Old 4th May 2019, 11:30 AM   #2041
Zen Mod is offline Zen Mod  Serbia
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Originally Posted by EmeryBB View Post
Yup IRFP250.
50W per TO247 package is highest I'm good with , whatever actual temp. is
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Old 4th May 2019, 10:52 PM   #2042
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Originally Posted by EmeryBB View Post
...I have 35V output cap on the big MoFo, do I need to change it to higher voltage to accommodate the higher B+?
Check it. IIRC this cap only blocks the DC Volts across the choke, which is surely 2V or less. So you need >2V rating.

An extreme (real unlikely) case would be large 0.1Hz signal which would try to swing large voltage into the cap with little voltage out. *But* you would need about a literal Ton of choke to support such swing, so this won't happen.

Start-up may try to swing voltage but again the choke won't support it for long, and electrolytics are pretty good about short-term overvoltage (big caps take time to heat-up).

For military work the cap must support the "ripple current" which is the audio current to the load. A physically large cap is normally fine all across the audio band. And in unclipped speech/music the average (heating) current is less than 1/10th of the peak current. Taking peak as 3A then the "average ripple" is 300mA and any speaker-size cap will stand that for decades. (For reference: a cheap 1000uFd 16V cap can carry 890mA, a 4,700uFd 35V 2,700mA, steady.)

In global NFB amps we sometimes use an output cap as small as 1,000uFd, but this is a deluxe amp and I assume >4,000uFd is typical for negligible loss and good damping to 40Hz.

So a >2V cap is probably fine, but uncommon, and too small to be impressive. 1,000uFd 6V is rated 500mA and might heat in steady test-tone power output tests. 4,700uFd 35V will take steady full output so is "overkill" for speech/music, and that's fine for us.
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Old 5th May 2019, 03:57 AM   #2043
EmeryBB is online now EmeryBB  Australia
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Thanks PRR, it's "Kick" from the choke I worried about, that's why I over rated the output cap. Looks like I have been worrying too much.
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Old 5th May 2019, 04:29 AM   #2044
xrk971 is online now xrk971  United States
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I have read somewhere in this thread Michael had build a version with 36V @4A
Perhaps that was the MOAMOFO and I run 37v at 4.65A and use a big 600w IXYS dissipating about 150w and cooled with a CPU cooler.

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I just made a new power supply called the SLB that can provide 4.4A with only 1mV ripple and two 15,000u bulk caps. This could be very useful for MoFo.

The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB
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Last edited by xrk971; 5th May 2019 at 04:32 AM.
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Old 5th May 2019, 05:38 AM   #2045
nautibuoy is online now nautibuoy  United Kingdom
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Originally Posted by xrk971 View Post
I just made a new power supply called the SLB that can provide 4.4A with only 1mV ripple and two 15,000u bulk caps. This could be very useful for MoFo.

That's why I was asking about the possibility of a single positive rail version of the SLB over on your SLB group buy thread.
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Old 5th May 2019, 06:19 AM   #2046
xrk971 is online now xrk971  United States
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Jhofland will make a single rail layout now that I have verified that the design works.
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Old 5th May 2019, 06:20 AM   #2047
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Default Adjustements

Good evening, gentlemen.
I ask the question again because modified alienation.
For the Mofo (version 19 Volts and 193 T Hammond).
I just tested a linear alimantation with a 300 VA transformer (2 x 15 vots) plus a diode bridge and a 44,000 F filter.
I mounted a series of resistors to drain 1.7A, the voltage is 20.5 Volts in charge.
For this voltage there, the 1.7A setting is correct?
By thanking you in advance.
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Old 5th May 2019, 02:01 PM   #2048
6L6 is offline 6L6  United States
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20.5v PSU voltage will work very well.
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Old 5th May 2019, 02:14 PM   #2049
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Default remerciement

Merci
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Old 7th May 2019, 05:09 AM   #2050
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Chokes and heatsinks arrived, should i be scared .
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