Re: Output stages voltage for reference

Soundararajan Ra.
 

Thanks john for your comments and suggestions .
soundar
vu2rjw

On Sun, Jan 8, 2017 at 1:36 PM, iam74@... [BITX20] <BITX20@...> wrote:
 

Very good.

Check out the variants of this amplifier on the web. There are many, ranging to 400 W. or more. Check the BITX messages and files for some. Usually the maximum voltage used is 48v; but that is for multiple units. 20-24v. is the maximum for a single unit. 19-20v. should work FB.

Look at the voltage on the gate. It should be ~3.5-4.5v. I wouldn't try to tweak this very much. If you are going to change things here, check the impedance of the drive. But it is not a thing to do lightly.

Since you are feeding it into a 50 ohm load, it should work. However 50 ohms at the output of the LPF is not 50 ohms at the drain of the IRF510. So you may have to make some adjustments. Make very sure you are matching your antenna to the output.

Usually some kind of relatively high voltage capacitor (mica?) is connected at the drain to compensate. Also to suppress ocillations, especially VHF oscillations. Try about 470 pF. to begin with if there are signs of trouble.
Watch out for spurious oscillations; they are easy to generate!

You will need a much larger heat sink to handle 20 W.

Try it and see what happens. Have another IRF510 handy to replace it if it blows. If it does, back off the bias a bit and it should work fine.

An alternative is to build a Class D amplifier, but that is relatively complicated. Another alternative is to replace the IRF510 with a RF MOSFET like the RDHFFxx series. But these are usually limited to 12v. and lower wattage. And the input would have to be adjusted to compensate.

I have found that the original International Rectifier devices are the most reliable. But, again, they are not consistent and have wide variances. There are many makers of these devices. They are very popular, and the quality available is wide-ranging.

john
AD5YE

 ---In BITX20@..., wrote :


today i fed 19volt to the IRF power supply using laptop powersupply unit. .Power output of 15 to 20 Watt was read in my sx200 diamond swr meter.
Is it necessary to adjust 0 singnal current of IRF (idle current) ?
When i fed 12v volt IRF 510 current is 85ma..


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