Re: If the IRF-510 is blown will the radio output anything at all?

Jerry Gaffke

There's a few milliwatts of 7mhz going into the base of Q13.
So Q13, Q14 or Q15 could be blown, and unless your rig is well shielded (doubtful) you will hear it on a nearby receiver.

If you can press the PTT button and see 100ma (or much of anything) going into the PA +12v (into the IRF510 drain),  then the IRF510 is probably ok.

Q13 can blow if a nearby QRO transmitter injects a few volts of RF into the base, maybe add diode protection described below
Q13 runs kind of hot, quiescent current causes it to dissipate more than the SOT23 package is rated for, maybe make it a 2n3904 in the TO92 package.
Q14's emitter resistor is likewise running hot, maybe go to a 100 ohm 1/4 Watt resistor.

You might check this post:
for voltage readings through the transmit PA.
Start with just the DC voltages (with PTT pressed).

If it was a nearby transmitter blowing Q13, you might check this out on adding back to back diodes for protection:
The idea was originally from Raj:
His incandescent bulb increases it's resistance drastically when it heats up, so is worth considering in addition to the diodes.

I'd be suspicious of that new power supply, obviously.
Perhaps it momentarily went to 20v when you first turned it on?
That would be bad.

Jerry, KE7ER

On Mon, Aug 14, 2017 at 10:01 am, <joshuaclough4@...> wrote:

First use I know everything was working and it was moving my SWR/Power meter.

Second use, I upgraded my power supply to a 12v 3.5amp. Little to nothing moving.
Switched back, still the same.
I was assuming the IRF-510 was blown since that seems to be the easiest thing to do with these.
But I can still see my ssb voice modulation (now weakly) on my sdr which is in the same room.
Is there anyway my (cheaper rtl-sdr) SDR is picking up something from the radio anyway? If what I said is even the problem?

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