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Marsfrogie 27th March 2008 10:37 PM

Starting a First Watt F3 build and need some help
Hello all. I'm getting ready to start a First Watt F3 build and have a few questions about some components. On a scale of 1 to 10 I would rate my knowledge of electronic components at a 3 so take it easy on me. I just want to make sure I'm not buying the wrong stuff.

For resistors I'm using metal film where possible, metal oxide for higher wattage resistors and ceramic where that's all I can find. Is this ok?

For the potentiometers I'm using these. Are these OK?

Family Rotary - Linear
Resistance In Ohms 5.00K
Power (Watts) 0.25W, 1/4W

Will this work for the inrush current limiter?

Family Inrush Current Limiters (ICL)
R @ 25C 15 Ohm
Current - Steady State Max 3A
R @ Current 0.335 Ohm
Tolerance 20%

Is this bridge rectifier ok?

Diode/Rectifier Type Single Phase
Voltage - Rated 200V
Current Rating 35A
Package / Case MB-35
Packaging Tray
Speed Standard Recovery >500ns, > 200mA

Thinking about using this transformer:
AVEL's Y23 series power
Load Capacity: 160 VA
Secondary Voltage: 18V + 18V
Dimensions: 4.0" D x 1.7" H
Weight: 3.3 lbs.

Probably will use a stepped attenuator for volume control. Hopefully it all works out ok. Seems a little overwhelming right now but these projects normally seem to come together with parts in hand. Thanks for any help and thanks Nelson Pass for your great contribution to the DIY community.

MikeW 28th March 2008 12:31 AM

You can get most of the parts from Digi-key or Mouser. You will need a bigger transformer >300 VA or 2 of the 160's. Get a CL_60 thermistor. I have extra if you need one.

Marsfrogie 28th March 2008 01:11 AM

How does this one look?

400VA 18+18Vac secondaries. Dual 115Vac Primaries.

I can't seem to find a CL60 thermistor on digikey. Does it go by another name?

Marsfrogie 28th March 2008 01:34 AM

I found the CL60 at digikey, Thanks.

Marsfrogie 28th March 2008 01:54 AM

Also thinking about picking up this heatsink and running a bandsaw through the middle. Seems like it would be almost perfect.

Marsfrogie 1st April 2008 01:56 AM

I have been making some more progress on getting all of my parts together. Picked up a 400VA transformer and tracked down the LU1014's. I decided that I'm going to build the heatsink out of some aluminum stock I have lying around.

On the F3 schematics it says that the R5 is matched to the JFET. How do I do this?

Also, how do I adjust the 5K trim pots?

One other question, on the stepped attenuator for volume control, I should match that to the output on the CD player correct? Which in my case is 50K.


MikeW 1st April 2008 02:06 AM
The answer to all your questions are here.:wiz:

Do not underestimate the size of your heatsink. The ones I have are 11 inches x 11 inches x 2.5 inch fins.

Marsfrogie 1st April 2008 02:41 AM

This is what I had in mind. How hot do yours run? Have you measured? Thanks for the link!

Marsfrogie 3rd April 2008 02:21 AM

Bear with me here. I've been reading the Z9 manual but it only has 1 5K pot in the circuit. The F3 has two and one more IRFP240 than the Z9. Do I measure the drain on Q5 and then adust P2 until the drain on Q3 is half? I am rather confused and don't want to smoke anything.

Thanks for clearing this up.

Nelson Pass 3rd April 2008 03:01 AM

The extra Mosfet in the F3 is the power supply regulator.
The extra pot is for trimming the gain of the current source.

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