Re: Something has been blown

Arv Evans

César EA3IAV

I would not worry too much about using Ebay sourced IRF510s.  Apparently
International Rectifier no longer makes the IRF5xx line of devices but has
licensed Samsung and others to manufacture them.  Many of these licensed
units then become available through Ebay vendors.  In modern solid state
manufacturing most all devices are tested with software controlled test
setups so possibility of a bad device reaching the marketplace is much less
than was the case in past years. 

It is possible that only one of your MOSFETs is bad.  This could explain the
ability to adjust current and current flow when the PTT is activated.

A power supply that has current limiting might be a good way to power your
BITX.  Something around 3 amps should be adequate to keep from frying the
MOSFETs and still be adequate for normal operation.

Strong near-field reception is normal as long as there is some signal being
generated.  Leakage through power cables and control wiring is locally 
quite strong, even if the finals are not working.  If only one IRF510 is working
and you are adjusting the bias as if two were working it could be that you are
running that one device in a relatively linear mode due to higher than normal
current.  This could also explain strong signals on a local receiver. 

Arv  K7HKL

On Fri, Jan 26, 2018 at 12:31 AM, César EA3IAV <Cesarleon@...> wrote:
Hi follks for the the ideas!
Antenna was matched with less than 1.4 swr
transistors were isolated and tested.

The only thing I can think of is that maybe, before considering to have the fets atached to the box I may shorted them by accident while initial testing

One doubt: even if they are blown, why i can transmit and be received in a nearby receiver? is it possible?
why it drains power if they are blown?

maybe it is just ine of them blown?

this afternont I will inspect tracks. I have some spare irf510 from ebay, but i was trying not to swap them because I don’t know if they are legit and the checking scenario could go very crazy with errrstuc fets...

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