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Nelson Pass F3 amplifier help wanted
Nelson Pass F3 amplifier help wanted
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Old 1st September 2017, 08:50 PM   #21
JeffYoung is offline JeffYoung  Ireland
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Nelson Pass F3 amplifier help wanted
What's the voltage across the resistors that are getting hot? (They're all in parallel, so you can just measure any one of them.)

Also, what's the voltage across the one at the bottom which is also discoloured? (You should read about 21V here.)

You could also check the voltages on the JFET (the small transistor hanging off the board just below the smoking resistors). You should get about 3.5V at the D, and about 1.1V at the S.

Report back with results.

(BTW, Nelson posted the F3 schematic and some other good stuff here: Pictures of a >>GENUINE<< Lovoltech LU1014D Wanted!)
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Old 2nd September 2017, 01:58 AM   #22
russell66 is offline russell66  Australia
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Ok
So #1 and all the parts that attach to the heat sink need to be isolated with the small light blue pads, if any metal touches the heat sink it will cause a short?
The blue pad allows heat dissipation but stop electrical current?
#2 The Pcb should be lifted away from the heat sink so as to avoid unwanted contact from the rear solder points to the heat sink?
How should this be achieved as there is limited distance available because of the metal tag lengths that attach the black parts 1 to the PCB?
What is the optimum distance as the PCB always looks close to the heat sink on other amps I have seen?
How could I dismantle and test as the black parts attached to the PCB always need to be attached to the heat sink don't they to avoid over heating?
What is #3 called perhaps PSU??
#3 does seem to have enough clearance from the chasis but should I add more?
Any links to pictures or advice on re build it properly would be could as that is my intention, also should I consider adding any parts?
It is normal to have the PCB mirroring each other or should I turn one of them?
As always thank you for the help, i am really enjoying this Forum I wish I had found it sooner.
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Old 2nd September 2017, 02:14 AM   #23
2 picoDumbs is offline 2 picoDumbs  Australia
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1) Yes, but use the keratherm pads from the diyaudio store. The blue silicone pads are rubbish.
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Old 2nd September 2017, 02:15 AM   #24
2 picoDumbs is offline 2 picoDumbs  Australia
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2) Absolutely. You've possibly destroyed a few components. 5mm bare minimum. Use stand offs.
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Old 2nd September 2017, 02:17 AM   #25
Soundhappy is offline Soundhappy  France
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Nelson Pass F3 amplifier help wanted
Blue pads is only for transistors.
Components like resistors, capacitors etc.
on the pcb's can't touch of conductive heat sinks
Better if your transistors from pcb right side be in the same position of the left one.
Psu resistors is rated 5 watts that little short if you can change
for the same resistance value but more power say rated 10 watts or more.
Twist audio wires outputs RCA and speaker as well. See First Watt excellent quality builds and inspire
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Old 2nd September 2017, 02:18 AM   #26
2 picoDumbs is offline 2 picoDumbs  Australia
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Read one of 6L6 build threads. It should answer nearly all your questions
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Old 2nd September 2017, 02:20 AM   #27
Soundhappy is offline Soundhappy  France
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Nelson Pass F3 amplifier help wanted
Quote:
Originally Posted by 2 picoDumbs View Post
Read one of 6L6 build threads. It should answer nearly all your questions
Yes Thanks 6L6

The diyAudio build guides
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Old 2nd September 2017, 02:21 AM   #28
Zen Mod is online now Zen Mod  Serbia
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Nelson Pass F3 amplifier help wanted
that service is too complicated for complete novice
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clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
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Old 2nd September 2017, 02:28 AM   #29
Soundhappy is offline Soundhappy  France
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Nelson Pass F3 amplifier help wanted
Quote:
Originally Posted by Zen Mod View Post
that service is too complicated for complete novice
Yup maybe 2PicoD can restore them for good working and safe.
Cost is small only one zillion $$$$$$$$$$$ me joke
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Old 2nd September 2017, 02:32 AM   #30
grimberg is offline grimberg  United States
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The Lovoltech's heat sinking requirements add to the complication. It has short leads which, I am guessing, is the reason the original builder did not use standoffs.
russell66, there should be 4 transistors touching the heat sink. Three identical large ones (IRFP240) and another, much smaller. Could you take a well lit picture of that one? Any changes to mounting the PCB will be restricted by that device.
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