Re: IRF510 amplifier failures

Arv Evans
 

Interesting comments thus far regarding IRF510 failures. 
  • Power supply current limiting (2.5 to 3A) seems to work.

  • Bias voltage shutdown on high current (3A) seems to work.

  • Driver impedance to IRF510 gate should be quite "stiff".  Use a 50 ohm pad.

  • Use small resistance (4.7 ohms) in series with each IRF510 gate lead.

  • Keep IRF510 leads short.

  • Impedance presented to the IRF510 drain should be 12.5 ohms.
    RF output transformer should be 1:2 windings for 1:4 impedance transition.
    Binocular core may work better...?

  • Avoid the problem by using some other MOSFET.

  • Use plastic fuses at 3A for self-healing action.

  • Fuse rig power at 2 to 3A to avoid IRF510 failures.
Some of the on-line information also mentioned low level background noise being
generated by MOSFET RF PA stages that remain powered during receive mode. 
Possible solution here might be to add a MOSFET switch in the DC power lead
going to the IRF510s so this power could be shut off during receive.

All good info.  Now how to keep within the original BITX objective of making rigs
that can be afforded by those with limited spare cash and still make them reliable
and inexpensive.  This solution(s) has potential for modification of existing
transceivers, and for future redesign of the similar units.  It also has application
for designing and adding homebuilt RF amplifiers for your BITX rig.

Arv  K7HKL
_._


On Fri, Jan 26, 2018 at 10:32 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
The RD15HVF1's should be operated at not much more than 12v.
At 12v, the IRF510's would survive just fine with no antenna connected.
That's an infinite VSWR.

So not obvious that this is a solution to blown FET's.
Though I do think the the Ids curves go up more slowly as Vgs increases on the RD15HF1's,
which makes RV2,RV3 not so touchy.
And the RD15HF1's might be easier to drive at 30mhz.
If you do swap them in, let us know how much power you get at 30mhz.

Jerry, KE7ER

On Fri, Jan 26, 2018 at 03:54 am, KD8CGH wrote:
Wouldn't it be better to change to a RD15HVF1 for high VSWR


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