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Here are some waveforms of Q507 from a working QMX+.? All are of the transmission of a single 30wpm 'dit'. My supply voltage was about 11.7V, scales as labeled, with zero baseline one line up from

thank you for the link Stan...73 S

I hit the 510s with circuit chiller while it was acting up.? No luv. Hit the rest of the amp parts as well.? Nothing. -- regards, Bryan, N0LUF

Thanks Ron. I will do that. :)

For some time (several months) I had what I thought was some intermittent QRM, where the band was covered in spikes spaced exactly 100 Hz apart. Here's how it presents itself in the WSJT-X (there

Okay Nick. I appreciate the quick response. I need to put the radio away for the night anyhow but i think if i find the source of the transmit problem, i may find the source of the receive problem as

Now take this with a pinch of salt, but looking at the component values in the QMX+ a DAC output of 1.92V into the base of Q513 should turn the TX hard on. ?However it’s late in the evening here

Hi Joel, with your measurements the VGS of Q507 is -1.3V, which is not enough to turn it on. The specs for the FET are -1.5 minimum and -2.5V typical. The modulator circuit is to my understanding for

Would love to be part of a group buy. 72/72 de OZ1ES Erik

BTW, one more thing....What sort of signal and p.p. voltage should i see on either the base or emitter of those transistors? thanks. VY2KW wrote:

Hi nick. I have tested and yes, R506 and R507 coincide with the source and gate voltages at Q507. The next step i guess, will be to check the gate of Q507 with my scope and see if i am seeing a

I should add that when installing the new pads, test for shorts and reset the bias. Too much bias can cause excessive heat.

Bryan, I suspect that the connection to the heatsink is the problem.? It should be getting warm.? Try resetting the IRF510s on the heatsink.? I also suggest switching to AlN (Aluminum Nitride)

Thanks for confirming Gus, I've been waiting to hear back from you. I've now got a new PCM1804 chip and I'm plucking up the courage to have a go at replacing it.

Just following up to confirm that what I had previously expected was the actual culprit. A bad PCM1804 was causing the AGC to engage constantly resulting in almost no signal reception on all bands.

Lidiette, try it with only a dummy load attached and see if the problem persists. Ron [email protected]> wrote:

Ok, so the BNC connector was a little bit loose. I re-soldered and it is firm.? I connected the antenna which it is the antenna that I currently use for my home base station. I connected the qrp

Scott, See the description at this link, which is on the QMX page regarding a fix to a 20m receive sensitivity issue: https://qrp-labs.com/qmx/qmx20m To take proper advantage of the new windings, you

Thanks Len Cheers Paul

Yes Paul, there is a DC short between the center pin and ground of the BNC……but NOT at RF. Len KJ9E