I'm pretty sure I know the answer, but good to ask anyway..
Can I use a QDX as the input to the 50w to test??

Vince

Hi Vince,

I have used the QDX to drive the QRP-Labs 50-watt amp.? Hans warns that the 50-watt amp is not designed to handle the high-duty cycle of FT8 or other digital modes.? I supplied 13.8 volts instead of 16 volts to reduce the power.? This worked well.

You will still need to be careful of very high mismatch antennas, as the mismatch can be reflected back to the QDX.? There is some interaction between the output and the input of the IRF510s.? You can also reduce the voltage to the QDX to reduce any stress on the QDX output devices.

I remember reading posts on this reflector with issues with the PTT (Push To Talk) signal from the QDX, so you may need to verify proper levels and drive capabilities.? I did not have the issue.

I have since gone to a multiband WA2EBY amp to take better advantage of the QDX band capabilities.? It has a COR (Carrier Operated Relay), so I do not need the PTT line.

73
Evan
AC9TU

Hi Evan,
got it..thanks for that..
1.? I think i've an issue with PTT on the QDX, I don't have a mini or qcx + handy that is built...have them both in the bag, I've been building QDXs for people
now building the 50w amp for someone.? With My QCX mini i was able with no issues, as built get PTT to work with my amp, but SMOKED the finals when adjusting R5...waiting for more finals from Digi-Key, and don't want to blow up this persons amp, but did want to get the PTT to switch the Amp to transmit. (haven't gotten it to do that).

2.? I also have a WA2EBY amp, it is sitting on the shelf..it works fine. but didn't want to use it with the QDX..so I'm glad you have used it..
gotta figure the PTT out
I'm not reading any voltage that gets pulled down outta the QDX on the RING..(+5 should go to zero)..it is pretty much zero
there is a setting in the testing that says on the cofiguration tab PTT Port as Serial 3..it was disabled, i enabled it, but still nada OH...duh..
just found it on the Band configuration...
I'll try that...duh missed that..

V

ugg...didn't make a diff...better read some more.
V

Hi Vince,

The WA2EBY amp does not need the PTT line.? The QRP-Labs amp requires +5 volts to turn on the amp and 0 volts to receive.? That is configurable in the QDX Band Configuration screen.??

NOTE:? The QRP-Labs amp is different than most amps.? Rather than pull it down to turn it on, you need to supply 5 volts.

73
Evan
AC9TU

that is the issue..
even in Band Config with PTT Transmit enabled (should be 5v) when PTT or transmit..zilch..zero volts..no 5v..

V

and i understand the WA2EBY doesn't need PTT..
V

Any COR-type of T/R control will to some extent "hot switch" the amplifier, driver and relays, since the RF drive must already be present to be detected and to actuate the relay.? So there will be a time when the driver and amplifier will both will see an open circuit load as the relays switch over.? Depending upon the relay sections' timing the amp may see the open load and RF drive simultaneously as the contacts bounce and settle.? Turn-off is not so bad since the RF drive will have gone away before the switchover.
For this reason I use a hard wired TX signal to switch my amplifiers.? It would be easy enough to modify the WA2EBY circuit to apply a 5V TX signal to the Q3 relay driver base through a 1K or so resistor.
73, Don N2VGU

To answer your original question, yes you can use the QDX to test the 50-Watt amp and set the bias.? The caveat is the amp needs set with NO DRIVE.? It needs switched to transmit without sending it any RF.? If you are on the "transmitter test" screen in the QDX serial screen you should be able to press "p" for PTT without sending any RF.??

That was what I was doing..Just to test the PTT to get the 50w TX led to illuminate..
The problem stems from the QDX, as i'm not getting the 5v from the PTT of the QDX..even with the setting in Band Config..(trying 40m) to match the 50w amp..
I'll try a different band..but not expecting anything different.?

I'm all good with the WA2EB amp..thanks for the info.

Vince

Alright, Vince.? Good luck with it.? I notice that part of my response got buried below the quoted text button.? I'll just ask again in case you didn't see.? Have you checked the QDX directly (before your PTT cable) or only after?

I do not have the schematic handy, but I believe that there is a pretty sizeable (4.7K?) resistor in series with the +5V output driver which may not be able to drive your amp control inout.? You may need to reduce the value or make a simple FET swtich.
73, Don N2VGU

There is a 470ohm resistor to limit the current through the BSS84 MOSFET.? It should work.? Try measuring the voltage without the 50-watt amp connected.??

Also, the plug on both devices is a stereo TRS so the TRRS cord will cause issues.? It would be best if you had an actual stereo cord, not a smartphone cord.

73
Evan
AC9TU

开云体育

Not sure this is your problem, but I’ll share just the same. ? If it seems right, I’ll try to find the original thread I started. ? ?I had two different QRP lab 50 watt amps that would not “turn on” even with the qdx sending the 5 volts. ? It turned out to be one of the transistors in the amp that failed, and caused a low resistance to ground. ? Not a short, but low enough that the QDX could not provide enough current to trigger the amp. ? ?Funny part was, and what really had be going in the wrong direction, a QCX could provide enough current, and the amp functioned normally with the bad transistor. ?

No I didn't check the QDX PTT line before connecting..only after..

Thanks Don,
I'll take a look..

Evan,
Thanks...
Just using a stereo TRS not a TRRS..
The issue is without the amp connected..no 5v out of PTT from QDX..
Havent had time to look at the the last day or so.
v

All,
Thanks for the help..so ..
Trying to watch the TX on the 50w when using the QDX...DUH DUH DUH...found the short between the headset.ttt
I was using the (T)ransmit on the Transmitter test..
which for some reason didn't key the PTT..
I tried the PTT and got the TX to illuminate as expected on the 50w..
thought that using (t) should have enabled the PTT....

tried again...all is well with the (t) keying the transmitter via PTT and Transmitting on QDX..
thanks all
Now to the other where I'm not getting the Audio and RF filter sweep to function which has no RX but TX working ok..on another thread message

Vince
vince

Ok..
so One QDX did not provide 5v for PTT..
changed out Q12..no help..
The person didn't need the PTT on the QDX so problem has been deferred.
thanks all for the suggestions.
vince