F5 power amplifier

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#2,521
Hi,
clip the Gate lead on the Mosfet short, 2mm from the thick part.
Clip the gate resistor lead short, about 3mm, and solder this short end around the 2mm stub on the FET.
Attach the flex wire from resistor to PCB
Add your insulation sleeve over the gate stub/resistor/soldered flex lead end.

This very short connection from gate resistor to gate, reduces lead inductance. It's lead inductance between the gate and gate resistor that causes the oscillation.
 
#2,522
OK,

thanks AndrewT and others.


Question: If I do change from resistor on PCB to resistor at mosfet, I just put in a link on the PCB where the resistor was?

And would 50R be ok instead of 47R (no more of them left and I have a good number of 100R dales I can parallel)


Gate would be pin 1 on both, right?


Fran
 
#2,526
jackinnj said:

TNX,
I have had to raise some prices -- I am out of my OLD stock on the IRF/Vishay HEXFET's -- and since Vishay took over IRF's discrete products the prices have really shot up. (Pretty unbelievable if you look at the bomb Intel laid on the market, but discretes is discretes.)

I think 1 shipment may have gone astray over Christmas -- have been away for 2 wks.
Click to expand...
_____________________________________________________

I see matched pairs of 2SK170 and of 2SJ74 for sale under
"Small Signal Transistors and JFETs" but no matched 2SK170 to 2SJ74
pairs for sale? :bawling: Would it be possible to order matched Ps to Ns? and at what cost?
 
#2,530
ichiban said:

_____________________________________________________

I see matched pairs of 2SK170 and of 2SJ74 for sale under
"Small Signal Transistors and JFETs" but no matched 2SK170 to 2SJ74
pairs for sale? :bawling: Would it be possible to order matched Ps to Ns? and at what cost?
Click to expand...

I'm trying to peddle as fast as I can.

NP said that it is probably NOT a necessity to match the N and P channel JFET's for Idss or gm -- I don't want to second guess "the great one" but I need to demonstrate it for myself.

This is a remarkably simple and high quality DIY amp to get going -- and I have 4 of them in operation.
 
#2,531
Tonight I got the feet made for the amp. I'm doing a similar line to the ceraball type set-up.

The "feet" themselves are discarded plugs from a replacement part in an instrument in my workplace. A ball sits on the top of them and then that whole lot sits into a alu cup.

The parts:

An externally hosted image should be here but it was not working when we last tested it.


So the alu cup screws to the bottom of the amp (ie its upside down in the pic) and then the feet/ball sits up into that. Assembled foot, again, upside down:

An externally hosted image should be here but it was not working when we last tested it.


The idea is that the ball acts as a point isolation and the o-ring gives lateral isolation. the whole thing is height adjustable for levelling.

the 4 feet:

An externally hosted image should be here but it was not working when we last tested it.



More assembly tomorrow night!

Fran
 
#2,533
I think this one will work.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BC2313-ND

The one I bought doesnt seem to be around anymore.
Uriah

edit:
Wait. Here is my post asking if the one I found was alright. Zen said not to worry and that if it sees much current then I have more problems than a wimpy thermistor
http://parts.digikey.com/1/parts/953076-thermistor-ntc-1k-ohm-5-mf52a102j3470.html

http://parts.digikey.com/1/parts/953076-thermistor-ntc-1k-ohm-5-mf52a102j3470.html
 
#2,537
Peter Daniel said:


Both in F3 and now in F5 I'm using IXYS. Bought them years ago through the forum, but I guess Percy carries them too.

I intend to also try discrete diodes.
Click to expand...


Hey Peter, you are usally good about this kind of thing. How did you attach the wires to those pointy bridges? I've some myself and all I could think of doing was bending the leads and wrapping the wire around it, then soldering.
 
#2,539
Use these or new Pannys?

I have four each of these beasts.
100,000MFD @ 30Vdc and 61,000MFD @ 55Vcd
Six inch height and three inch diameter.

Should I save forty dollars and use these if these don't
test leaky OR should I go for new Pannys 15kUf~22kUf ?
 

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#2,540
It'll give a number of people here hives to hear me say this, but I've used old caps on a number of occasions and had no problems. If they poop out on you, it'll smell bad and you'll have to buy new ones, but as long as you're not standing on top of them when they vent, you'll live to see another day.
Moral of the story? If they've been sitting for a long time, apply voltage slowly, and at the end of several feet of wire.

Grey
 
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