EMRFD Message Archive 6519
Message Date From Subject 6519 2011-07-31 08:16:07 John low output IRF510
I've built a 75 meter QRP SSB transceiver called the 'California Board" by VE7ZM. It uses a 741 op amp after the mic, 602 mixers and a IRF510 and VN10KM for the PA. I've set the IRF510 at 20 ma. at rest and the VNVN10KM at 10 ma.- per the build instructions. I can hear myself with a separate receiver clearly but the max current draw (voice peaking) looks to be about 50 ma. not the 300 the author says to expect. My question is- is it more likely I'm under driving the PA (the feedback resistor on the 741 has the gain set to 27 not 100 (27K/1K)), I'm using a really cheap CB dynamic mic, and it's possible the IRF510 was static compromised. Should I try a higher gain mic, boost the 741 gain to 100 or replace the IRF510? I know it could be other things but these are my likely suspects. Any other thought are indeed welcome.
John Greusel
KC9OJV6521 2011-07-31 09:07:23 Ashhar Farhan Re: low output IRF510
(capable of dissipating 10 watts or so). Can you measure the output at
each succesive stage? That will allow you to narrow down to the
under-performing block.
20ma seems a tad low for a single ended IRF510. You might want to bump
it up to 50mils.
Btw, it is possible that the IRF510 is already dead. At times, it dies
in a way that the input appears almost intact at the output.
I have long suffered the IRF510s until I switched to the JBOT amp.
They are tricky and unforgiving. They were never meant for this
purpose in any case. Never teach a pig to sing, it wastes your time
and it annoys the pig.
- farhan
On 7/31/11, John <greusel@sbcglobal.net> wrote:
> I think I could use some wisdom from this group.
> I've built a 75 meter QRP SSB transceiver called the 'California Board" by
> VE7ZM. It uses a 741 op amp after the mic, 602 mixers and a IRF510 and
> VN10KM for the PA. I've set the IRF510 at 20 ma. at rest and the VNVN10KM at
> 10 ma.- per the build instructions. I can hear myself with a separate
> receiver clearly but the max current draw (voice peaking) looks to be about
> 50 ma. not the 300 the author says to expect. My question is- is it more
> likely I'm under driving the PA (the feedback resistor on the 741 has the
> gain set to 27 not 100 (27K/1K)), I'm using a really cheap CB dynamic mic,
> and it's possible the IRF510 was static compromised. Should I try a higher
> gain mic, boost the 741 gain to 100 or replace the IRF510? I know it could
> be other things but these are my likely suspects. Any other thought are
> indeed welcome.
>
> John Greusel
> KC9OJV
>
>
--
Sent from my mobile device6522 2011-07-31 11:04:19 JOHN GREUSEL Re: low output IRF510
Thanks for the suggestions. I'm somewhat challenged in the diagnostic equipment area.
I'll try swapping the IRF510 and bump the current a little and see what I get then.
John
KC9OJV
________________________________