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Hi everyone, My XPA125B unit is the one with the new circuit based on the AFT05MP075N transistor. Recently, during some operation on 80 meters band, I saw some smoke coming out from the amplifier. A bad day. After some PCB investigation, I could clearly see that the transistor was burned. The unit turns on, everything works, but in TX mode, it displays "low efficiency", it seems the damage is only to the transistor itself. I managed to import some spare transistors from Aliexpress (the exact same part number), I am planning to perform this maintenance myself. I need some help regarding the bias current adjustment. I believe I will have to adjust the bias current for the new transistor, but I am not sure about how to do it. There are two small potentiometers (trimmers) near the transistor location, as well as two jumpers. I wonder if they are there for the bias adjustment process. Does anyone here have already performed this process? Any suggestions on how to proceed, and what is the right bias current to be set? Picture below from the relevant PCB area: Thank you for your attention!

Hi, I noticed that when I connect my X6200 to the XPA125B amp with the amp set to the auto band switching mode, the display on the amp does not display the same band setting as the radio. For example, with the radio on the 80m band it shows 75/80m but flips back and forth between that and 60m. With the radio on the 40m band the amp displays 30m. Please see attached photo. Has anyone else experienced this? If so, has anyone discovered a fix? Thanks, Dave/K5HC

Having taken inspiration from Chris (DL6SEZ) and his Bluetooth keying solution for the IC-705, I thought I’d have a look at what I had lying around to see how I could replicate it. As I had a M5 Tough lying around doing nothing, I thought I’d start with that: I have taken one of K7MDL’s example sketches from https://github.com/K7MDL2/IC-705-BLE-Serial-Example and extended it to send a GPIO pin high on a similar M5 Core2 controller, using the Grove connector on the side when the IC-705 goes to TX. As a proof of concept, I have used that pin to drive a single relay, and it works well. This works even when running off the internal battery of the Core2, but I suspect the battery won’t last terribly long. However, now I intend to use Chris’ optocoupler and parasitic power circuit and put it on a small circuit board to sit in the bottom of the case of the M5 Tough, and replace the USB cable with a DIN6 cable to plug into the amp, and power the M5 from that and use the optocoupler to switch the PTT. I will also use a DAC output to take care of the band switching too, but I have yet to implement that in the code. I think this will be a nice way to reduce the number of power and signal cables, especially for portable ops, and I wanted to use this as a build log of sorts, and a way to get feedback from the community. I’ll post again when I have implemented the band-switching and have a PoC of that working. 73 Stefan MI0PYN

Had to send my 991a in for service, and it's taking a long time... So I got an X6100 for HF in the interim. That seems to work OK, except it seems a little ... unfinished. :-( I'm thinking about buying a XPA125B to give it a little more punch. Is that a good idea? TIA for your counsel! 73, Paul -- AI7JR

Hi All, I am new to this amp and am wanting to build a cable for switching it from a KX2. Looking at the manuals for both the KX2 and the Amp, I think this should be just a simple TRRS jack to a DIN6 cable, connecting R2 on the TRRS to pin 2 in the DIN6, and S on the TRRS to pin 6 in the DIN6. This is based on the following block from the KX2 Schematics, showing that R2 on the ACC port is not tied to a voltage rail, and is purely pulled to ground through some type of transistor when the KX2 goes to TX: If I have understood that right, I believe that the amp has pin 2 on the din pulled high normally, and that the KX2 simply sinks some current when it pulls that pin low. This is based on the section in the XPA125B schematics which shows the DIN connection: The thing which confuses me a little is the fact that there is also a 12v tie in on that pin 2 (through a 4.7k resistor), but the manual is very emphatic about not pulling that pin above 3.3v. This brings me to my 2 questions: 1. There is nothing on the KX2 that **COULD** pull pin 2 on the amp above 3.3v, right? It'll just float at whatever voltage is provided on it by the amp until the KX2 pulls it low as I understand it. 2. Is the circuitry in the amp as detailed above enough to limit the current that will be sunk by the KX2 when it pulls the pin low, to keep it below the max 100mA, or is an additional resistor required in the line to further limit the current? I believe the current sunk should be well below the 100mA, but I am not confident enough to read the schematic above and understand how pulling pin2 low switches the amp to TX and how much current is involved. I'm happy enough making a cable if my assumptions are right, but I couldn't afford to replace either the KX2 or the amp if I do get it, so want to make sure. Thanks for your help. 73, Stefan MI0PYN

Just received a brand new XPA125B from Radioddity. (11/1/24) Noticed that there have been some changes to the power wiring connections. First off, the rear DC power inlet is now ANDERSON POWER Poles vs the previous female 6 port connector. Second, the fuse connector on the rear of the amp has been eliminated and there are now TWO fuses on the supplied Anderson Power Pole power cable. This cable is now 12 gauge stranded black and red copper. The cable is as flexible as 12 gauge would allow. Each leg of the power cable (both black and red) has a hatched fuse port with 25A two prong automobile fuses. Lastly, that power cable is about 6 feet long with one end being Anderson Power Pole and the other end is bare with stripped wire just pulled back a tad. So there have been some power changes to the XPA125B! The supplied manual however, still shows the earlier rear fuse and white 6 port female power jack. I wonder if anything else has changed... Have not powered it up as I just got back from a POTA activation. Cheers, Art W1SWL

Hi, I thought I would share some information on this Linear that I've managed to get confirmed from Xiegu. I had a disasterous experience with this PA only a week old and it let the magic smoke out of the box. 3 watts of drive, 160 metres, 76 watts out, SWR 1.3 (Tuner and Amplifier engaged) Couldn't really explain why it let the smoke out until I dug further into the output finals. After much too and fro-ing with the Resellers (china) and Xiegu they have confirmed changes to this design. The latest XPA125b no longer has the Mitsubishi HHF100 Mosfets they have simplified the design from the dual devices to a singular AFT05MP075N package. This Mosfet is described as a 70 watt 136-520 Mhz device so if anyone can explain to me how exactly it's working at 100-125 Watts 0-30 Mhz that would be super....... The latest version of the board is labelled XPA125b AllInOne V1.05 although the reseller insists that Xiegu wont release the schematic which is a real pity. The Mosfet change, design and version number of the new board has been confirmed directly with Xiegu Customer Support. I can only conclude that I was driving it too hard at 3 Watts, that the output exceeded the 70 Watts the new package is rated at and that's why it let the smoke out. Very frustrated, reviews said it was a pair of Mitsubishi HHF100 (100 Watt rated) output Mosfets which resonated as a good design to me. My advice to anyone thinking about buying one of these is dont. False advertising, No Customer Support, Xiegu do not release schematics so you can affect your own repairs. I love my Xiegu X6100 but this amplifier is a nightmare. Love to hear from anyone that has had similar problems or has suggestions for repair. Trevor - VK8TH