I'm open to constructive criticism on this one... know a better way to git er done? Please share! Side note: this DID fix the issues I was having in the mobile. Love it when a plan comes together!
1. - move the rf off of the power switch, run coax from the relay to the input splitter. 2. - Delete the present bias circuit and install a regulated adjustable bias circuit. For best linearity and amp stability the bias supply needs to be stiff and provide adequate current and voltage stability. I usually also pull the boards , cut the plate out and re-orient the boards side by side and re-drill the heat sink. I also separate the input and output onto separate relays to give better input to output isolation and use a small separate relay to turn on the bias when the amp is keyed. I 've done a few like this and the tendency to self-oscillate disappears. BTW this is not criticism of your troubleshooting and problem solving skills which you have demonstrated are excellent. Just relating my experience. The Outcom OPA202 amp design/board that Texas Star built all their amps with was never that good of a design to begin with and the layout of the 4 pill versions of their amps just exacerbates the original flaws.
Bro im still learning from you all the time . On behalf of us newbs that are hustling everyday trying to learn...dedicated to learning this crazy stuff we call rf. With all its crazy properties. You are the very best teacher I've had thus far and its greatly greatly appreciated my brother
Using the antenna tuner to measure what's going on, define the measurements results with the VNA and THEN use the conjugate of the measurements. You do understand smith charts I would say. Well done!
I am way behind you with my learning curve but the way that you have explained what and why that you took this approach was understandable and surprisingly simple for my 60 year old brain to obsorb... I truely enjoy and appreciate the content that you so selflessly create for us... 73 my brother! Ps... I'll have some of whatever your dog is chowing on... Sounded delicious! Larry KF4LBG
Really good information, I wish it'll be more peoples like you that takes the time to explain and actually show the whole process of how things are done, good for you man
Excellent troubleshooting this tricky problem & Correction componet deduction with tools on hand !!! ....I also thought a Conjugate Capacitor 'bout 200 pF (--28 ohms) would be the required Reactance correction.....Your 170 nH inductor is also +28 ohms....Thx for posting video..
Great video! Its a complicated process that I have to watch and take notes, good I have learned something here. It would have been neat-o to see the Sim Smith figuring of the needed series inductance. Keep em coming.
I have the same issue with exactly the same dx500v ... Thank you for this video. I will have to now go watch some other videos and then return to this one. And hope i can fix mine.
Smiling! Good video on tuned input stuff. Thinking about building one for my old amp. Watch BBI and run across your stuff when he came for a visit and got the kit for the LDMOS amp you put together in a kit. I want to play with it some and been looking at some built by RF2K-s full 2kw and the mercure IIIs 1200 w. The price tag kind of out of my range for sure. Don't understand solid state amps, got my ham ticket when it was tube theory, but learning. Back in 1976 I built a amp for my old Yaesu FT 101B worked great and still does today. Now days running IC 7300 solid state and it needs a tuned input. I use a MFJ 949E for tuning the input. Much smaller than your 989C but would like to have a 989C for the other side of the amp, for playing with my long wire stuff running full power, Been looking but they are a bit more then I want to pay. My Home brew amp is a 160-10, 4-1000A with about 4000 volts on the plate, puts out about 1400 with 100 watts drive from the Icom. 73
Thanks for the passion of this "hobby" you have. I try to not be consumed by all this knowledge and excitement of learning this stuff. I have a question! How do you measure the nanohenery coil after coming up with the value needed from the SimSmith caculation? Like what tools or instruments are used to find the inductance before installing the parts. Thanks!
Same thing going on with a cheap chinese amp that was given to me to repair, a bj200. High swr when on low when off. Also, it got stuck in transmit, over heated and than died. I found a burned up diode and open cap bleed off resistor for the delay. Havent figured out why the high swr yet but had to order and wait for parts to come in. Not to mention whatever type of solder they use in the factory over there, is a pain in the ass to remove. Ugh!! Lol. Still havent found out why high swr but this video was a help. Thanks sharky
hi, i have a palomar hd450, runs four sd1446. two are hot to touch, so is the accompanied output transformer and caps.. the other 2 transistors, transformer and caps are about half as hot. it does nearly 400w. with 20w in. . could i have 2 soft transistors... the input swr reads 2 to 1..every thing else looks ok
I have an amp thats not pulling enough amps off my 150 amp supply its only pulling like 17 to 20 amps it should be pulling 30-35 amps what do I check sir?
Have you added a rf choke? Role up abt 10 ft of coax into a donut. That will prevent rf from getting rf into ur radio. You can add it to your coax. Won’t hurt a thing.
I would have liked to see the calculations and the process of the programs that you used the way you used them to get at the final outcome pf the inductor calculations; to make the circuit resonant.
I have a amp that does something similar when I deadkey input swr is 1.3 with a meter inline between radio and amp when I modulate the radio swr light comes on but the swr meter doesn't move much 1.3 to 1.5 not sure why this is happening or why the radio is showing high swr but the inline meter is not
I had never seen that schematic for a 500 before, (shows you how long I have been away from the business), so I stopped the video on the schematic and looked at it in detail. It appears that pressing in the SSB switch completely removes the dial a watt from the circuit even if the dial a watt switch is pressed in. So pressing the Dial a Watt switch in applies a 75 ohm resistor shunt to ground ( a 1.5 to 1 SWR excluding the connection to the splitter), and if the SSB button is pressed, the Dial a Watt pot is disconnected, so in that configuration, with only a single non-reactive 75 ohm load, it might have been easier to troubleshoot your input SWR problem. I enjoyed watching your method of troubleshooting the problem and coming up with what might be the perfect fix that may still be 'tweakable' by playing around with the spacing on the inductor you added.
Very good but all you had to do wad lengthen that coax about an inch and a quarter. Uie also didn't test another Amp with your radio if I'm not mistaken. There's a lit I would have done to check the problem before I used your method. Not that your wrong but it was probably just your antenna.
great video give yourself credit when credit's due trust me. You know what you're doing . Learn as much as you can that's what I do Always asking questions... I rebuilt a few texas stars myself. 2- 500s a modulator, 667 , and 3 - 250s... they work awesome. My latest is a 1600 Texas star. my Dei transistors blew out.. The only ones that blew out we're the ones on front board near switches and then the rear board were power cables exit blew out. The other two boards in middle perfectly fine. . Now replace everything that was burned up in there.. I put new HG 2879. And I had the front one blow out again..wtf Then I replace those two and the rear ones blew out again. Wish I knew what was going on.. Maybe I'm having a. Biasing problem? or I'm having a leak problem somewhere.? There was no RF going through the board when it burned up the first time . The power was on and it was burning but no RF.???? lol. I like your channel I just came across it thank you. It just made me think how hard it really is. Even though I have all the blueprints and the book for all the Texas Stars.. . Sometimes it's never enough. Keep up the good work I will be watching hopefully I'll figure this problem out soon.. it's starting to get real expensive buying another pack of HG 2879...lolol thanks
By the way i really enjoy your videos .. please keep doin what you do. I hope to some time in the future do a ldmos set up around 5kw would make me happy happy happy Take care. 199 florida georgia line.
Added an Inductor? When you are dealing with a 25 ohm load at the input signal splitter? 50ohm to 25ohm, 2 to 1 transformer would have fixed that problem. Then examine the output combiner...
The input transformers shouldn't have nowhere near that pf. 120pf to 330pf silver dipped micas is MAXX. 1200pf to 1500pf is way way to much for even a large output transformer. Mite Wana relook at that schematic.
Good job, I've always used trial and mostly error. Do the following to get reflected power to zero: Key up transmitter and insert a small ferrite rod slowly into your new inductor. If reflect goes up, spread the coil, if it goes down, squish the coil or add a turn.
Having a "Dial a Watt" on an amp is as smart as having square wheels on your car, makes friggen no sense. What was the Texas Star engineers thinking of???..🤣💨💩
I have watch a few of your videos, you have very good intuition in this area, very impressive. I am a Electrical Engineer and a Extra Class Ham and I can tell you that what you are doing is post graduate stuff, I also don't know very many Hams that can say complex conjugate much less spell it. Like I was saying your intuition is fantastic but your vocabulary is dismal, you use too many colloquialism and sang terms and you end up giving me a headache within like 5 minutes, it is pico not puff. I guess that is my problem not yours but if you are looking for constructive criticism that could be an area to work on. In any evet keep sharing because as they say, to teach is to learn twice.
It's amazing how CBer's use bizzare language (pill, thats what you take for a headache) instead of lets say output power transistors or MOSFETs or LDMOS and RF theory that is totally wacked. It's so simple to matched the input Z. Changing the coax from RG58 to that expensive stuff is just plain a waste of money, your only at 27Mhz, there is NO difference in line loss. I'm an RF Engineer and have been for many decades, be careful and don't kill yourself. Many have while working on RF gear.
I was told when I was younger and learning about electricity and anything that uses it was that you never see it coming and when it grabs you, it’s too late. Whether with wires or without them electricity is dangerous and you better know what you are doing.
