#96 Repairing a 1500 Watt MOS FET HAM radio RF Power Amplifier

In this episode we fix a HF PA with burned PCB and have to find the cause why it burned. Therefore we perform a lot of testing.
Native speaker choose 1,5 or 2,0 video speed.

[@zoranconjar6815]

An excellent example of how, with high knowledge and the possession of quality measuring and diagnostic equipment, you can achieve excellent results. Thanks for your time and demonstration.

[@MrCarlsonsLab]

Yikes, I bet those FET's a worth a bundle! Nice that it was just that board. Thumbs up bud!

[@TRXLab]

750 each...,Paul. Happy that these survived... Thanks for stopping by. Hey bud what's going on where are the new vids?? Take care 73

[@hankbizzo5]

Wow 2 of my favorite KZbinrs.. Thank you for all the great content, keep up the awesome work!!

[@mitch3064]

@@hankbizzo5 My thoughts exactly. Call me what you will but to me it is sort of like reading Issac Newton and Albert Einstein writing to each other(yes I know they could not do that). These two along with Dave from EEVBLOG, and ElectroBoom are my favorites, electronic Gurus.

[@andrewmullen5770]

Me too! They both provide so much information and inspiration. In my perfect life i would be doing these things for a living!

[@JustinRuth-km4wz]

Hello Mr Carlson you are amazing man. Listen we deal and work with the 188 ldmos chip ..I'm a big DX guy and build my own amps and modulators... Love your channel and what u do ..ur channle along with this one are by far my fav

[@carlos735]

The experts in RF Amplifiers are very rare and you are one of them, you got a new subscriber

[@KH07734]

I spent 4 years learning electronics in grade school. I use basically the same process you use to troubleshoot. My eyes are less than normal lately so Ibtake a bit longer to complete the tasks.

[@OldSweetTed]

I always appreciated my repair folks, but even more so after following along this diagnosis & repair!

[@TRXLab]

Thank you Jim! All the best and 73

[@justinruth9729]

This guy is next level technician...period prolly the best on entertainment

[@glitch1182]

This is amazing. Watching this video and how you methodically progress through troubleshooting the amplifier made me appreciate the work that was involved in its design and construction. I wish I knew enough to be able to build one of these. I don't know where to get a primer on filter networks, and I don't even have faith in my ability to build a power supply of my own design. Someone else's, absolutely!

[@TRXLab]

Thanks for feed back Ahmed. 73

[@lyntonprescott3412]

Fantastic repair way beyond my level of competence and understanding, but you explain things so well I can get my head around most of it. I bet you could make my old FRG 7 really sing! 73’s Lynton

[@mitch3064]

The suggestion for the changing of the video speed was spot on. Thank you. It actually helps in other ways. Somewhat often people on KZbin talk a little fast for my old brain, so your speech pattern, at 1.25 help smooth things out, and not be too fast for my comprehension. Your English is fantastic. My ability to sprechen Sie Deutsch ist sehr klein. Maybe 30 words left over from learning a bit from my girlfriend while I lived in the city of Bitburg for a few years. Nice addition to learning some of the language was that her father was a distributor for Bitburger Pils. 40 years of not using it hasn't helped.

[@TRXLab]

Thanks for the kind feed back Mitch and really glad that you liked the video! Hope you still enjoy Bittburger lol. Ich wünsche einen schönen Sonntag 73

[@dennisbauer3315]

That was better than watching a movie, It was good to watch and learn, thank you TRX Bench.

[@patrickpafarnis5798]

Again a very nice instructive video, however I'm a technician but not well-versed in high frequency technic, but your outstanding explanation did me understood everything very well. As I mentioned before with your explanation with the switching power supply, your english is for me as a dutchy, 100% understandable and more clear then a native speaker. Thank you very much!

[@TRXLab]

Hi Patrick, thanks for the feed-back glad that you like it. 73

[@MicheIIePucca]

You have some nice test equipment. The analyzer to view frequency and the SWR as you switch between the bands gives a cool perspective of health all at once. As always I find watching these videos so interesting, and entertaining, while at the same time trying to learn something more each time I watch one.

[@TRXLab]

Glad that you liked it Michelle! Thanks for stepping in 73

[@user-uv4xe3cq2y]

I must have missed the AFP re-adjustment that started the whole problem? Thanks Peter for another great video. I appreciate your attention to detail.

[@buckaroobonsi555]

That harmonic suppression is beautiful at that output power level!

[@TRXLab]

Right it is really not to bad. All the filtering is just working fine 73

[@randyterrell2261]

Peter, great video. Been playing with high power solid states PA's for years but still learned a lot of the newer techniques. Good job!

[@TRXLab]

Thanks for watching Randy! 73

[@binarybox.binarybox]

An excellent,methodical and complete repair, Peter. Very enjoyable to watch. Thank you. 73.

[@TRXLab]

Thanks for watching 73

[@montygore1200]

Hi Peter. All of your videos are very informative. This one to me really shows your extreme knowledge. I would love to own this amp. I wonder how many the old guy built. Perfect for a transistor amp. I would really love to own this one. The owner should be thankful for you knowledge and to own such a nicely designed amp. Very nice to see it repaired.

[@johngulliver6151]

Great video again I really enjoy your videos you are a very good engineer and your commentary is very clear to follow I sit and watch always with interest .Thanks again for posting

[@TRXLab]

Thank you John glad that you like it...73

[@EnochianBorg]

After going step by step watching this.... you did everything right. I suspect a roach climbed between that circuit and created a ground fault for a long enough period while the amp was not engaged on. But long enough to create a little mini heating element and the burn occurred. What I don't see in this circuit design is a fuse between the main PSU and this burnt circuit which would have blown at the current a roach would draw. The only flaw in the circuit design was lack of a fuse element after the main PSU to protect the entire system from fire hazard. I will be placing a correct fuse in my own system which is very much the same as this unit but half the output and of course 48 volts. Thank you for posting this video. It was very informative not only for repair study but concept design as well! Good job on the entire video and thank you. If it wasn't a roach then it may have been an arc caused by too much solder on the main (RED) wire that may have melted during or at the end of operation... then while the operator was asleep and the unit still powered... MAGIC SMOKE? He or she wakes up and suddenly the amp will not function.

[@TRXLab]

LOL yeah may be...Thanks for feed back

[@kingsqueak2221]

So thorough and takes a lot of time to put a careful video together as well. Very useful. I'm only just starting to understand so many concepts with amplifiers and information like this is very helpful. Thank you for doing these. All of this to talk to OMs, makes our hobby seem kind of silly really. :-)

[@g0fvt]

Great diagnosis, it is too easy to rush through a repair, well done for checking the low pass filters. 73

[@TRXLab]

Thanks for Feed-back 73

[@PhilipEvans11]

g0fvt hi I have an fm 250w- 300+ and it was given to me with a working amp with driver for spares the transistor blf25 are the same but -I wonder if you could advise me why side is rd in and out as there is 2 bnc on the case of The spare I no power around 30-46vdc input2-4w maybe less I want to add a LPF to it with power and drive

[@g0fvt]

The collectors of the transistors will usually drive the output transformer, the windings of that will generally follow a short path to the output BNC. Even if you get input and output connections reversed you are unlikely to damage the power stage as long as the drive is not excessive

[@SquantoTerror]

Great video once again! I really enjoyed your explanations and walking us through the procedures to test and repair this amplifier. Very well done! 73!

[@TRXLab]

Thank you very much Nicholas! 73

[@hamradio599]

I like your DCA55 component tester. It's really useful.

[@billharris6886]

A good power amplifier will have protection circuitry that monitors forward power, reflected power, input power, output power, output device DC current, output device power dissipation, and of course output device junction temperature. In most cases, the protection circuitry should reduce input drive to properly protect the output devices. The protection circuit should never abruptly cutoff power because, this can generate damaging transients. Instead, it should fold back ouput power like a power supply folds back current when the current limit is exceeded. With the amplifier you are working with in the video, the manufacturer may have set the cutout point at a specific reflected voltage on the directional coupler (which relates to a reflected RF power level instead of an actual VSWR ratio). For best reliability, output power should start folding back at VSWR ratios greater than 1.5:1.

[@jessiec4128]

That is one bad to the bone amplifier! Very nice equipment there.

[@lawrenceleo8468]

"Magic Smoke Escaped" I Subscribed and Hit the Bell the second I heard you say that :) . I personally have seen a 1 inch high flame come from one of those SMT ceramic capacitors; those little caps can do a lot of damage. You are an amazing technician and we are all blessed to watch you in action. God Bless You TRX ! 73 Lawrence VA7LTX

[@TRXLab]

Thanks for sub!

[@YvoMunizAlphaTelecom]

Another great video Peter! Very well explained. I liked your dummy load... I have a EKD-100 for restoring.73's

[@TRXLab]

Hey Yvo, nice to see you and thanks for your feed back! Yeah the RFT devices produced in the former GDR are really rough and good for heavy duty. Hope you will do a video on the EKD-100 nice SW receiver. Take care my friend 73

[@ThingEngineer]

Ooo what fun. Looks like maybe an arc over from high SWR caused a thermal runaway. Great video!

[@hancecrawford]

well done Peter that is good testing to check for earth leakage very important were safety is concerned I used to do P.A.T testing Pats stands for Portable Appliance and Testing.

[@N1RKW]

Well done! Good repair and good video, as usual! Thanks, Peter! I found myself wondering through most of the video what could have done that kind of damage, but then you found the SWR protection circuit was out of adjustment and the small, seldom used part of my brain that stores useful information realized that a high SWR situation could mean that there were some seriously high RF voltages playing around inside that amp.

[@TRXLab]

LOL yeah some seriously high RF :-) Thanks for stopping by Adam! Take care 73

[@subramanianr7206]

@@oldjarhead386 yes, very appropriate question and he had not shown the same on the video 🙄 De VU2RZA

[@gregorywest2029]

Great video Peter, like the safety test performed. Keep them comming. Thanks, Greg

[@TRXLab]

Hi Greg, thanks for stopping by, Yeah I always perform this safety test after fixing a device with internal 230V power supply. 73

[@michaelhawthorne8696]

Great video and some awesome test equipment. I thoroughly enjoyed that very well explained test procedure. I could be wrong but I don't think you reset the Pot to trigger the Thyristor for the AFP LED after turning it fully clockwise.

[@TRXLab]

Thank you

[@WB2GPU]

Your analysis and process of elimination is great. The only problem here is that there is no explanation for the blown board. It takes hundreds of amps to burn a gaping hole in a board that is mostly copper on both sides. Since it is a high current arc from the Antenna jack to ground, it would appear there may have been a nearby lightning strike. The protection circuits could do nothing to stop this. I don't believe the energy came from the internal power supply, I have to believe it would have folded back or popped a fuse. It would need to see a direct short and only limit the current to max for many seconds or even minutes to burn like that. That was a done in milliseconds.

[@billharris6886]

Hello Peter for making the nice video, with a thorough checkout of the amplier circuits. I designed some high reliability airborne power amplifers in the past and wanted to add a few recommendations. Since this amplier is for amateur use, the standards I recommend will be somewhat less but, still useful for general guidelines.

[@TheRadioShop]

Very detailed analysis of the issues Peter. That was a lot of testing to go through. You really did a good job of explaining that. You thing it may have just been a weak link in the board that caused the failure? Or maybe that tiny capacitor shorted?Thanks for the great video my friend.

[@TRXLab]

Hi Buddy thank you. Well really not 100% sure what the cause was as other than the pot for swr all turned out to be good.. May be it was a bad solder point on the burned board but that is not certain. Thanks for watching my friend. 73

[@thefreese1]

I kind of skipped through the video . Did he change out that potentiometer on the overcurrent board ? I would have changed them both .... That was a great Video . I'm building a LDmos amp using a Gemini style chip . Actually a BLF188xr .... Only thing I didn't like about this amp I saw was the single choke on the output board , but other than that , This is a well made, clean , amp....

[@llsdigitek]

Extremely thorough test, really learned a lot and enjoyed! Thanks - Lloyd W9NLA

[@TRXLab]

Thank you Lloyd 73

[@robertcalkjr.8325]

Nice work, Peter. Thanks for sharing the repair with us.

[@TRXLab]

Thanks for watching Rober. 73

[@tl2797]

3:49 oh WOW! Thank you for great videos!

[@jimsutherland501]

The world needs more people like you! Genius

[@TRXLab]

Thanks Jim!

[@Bass.Player]

Very thorough Peter, did you go back and adj. the SWR sensitivity pot with the PA on? Sorry if I missed it, I fell asleep for a few minutes. (Senior moment) K5AZE.... It's nice working on this low voltage stuff, much safer....

[@StreuB1]

Thank you very much, as always, Peter!!! Great video as always!! That is one impressive amplifier!!

[@TRXLab]

Thank you Brian! 73

[@tuberadiohistory8093]

Thank you for this interesting and detailed video. Great troubleshooting.👍

[@toastnotoflondon8500]

Excellent and informative. Thank you.

[@wildrootsfarm1975]

Good explanation of troubleshooting. Thanks for sharing your work. Impressive!

[@TRXLab]

Thanks for feed-back and watching 73

[@chickennugget3362]

Another great video! I'm going to have to watch it another 6 times for it all to sink in!

[@w.rustylane5650]

Do you have a dummy load that will handle 1.5kW? That's a very nice legal limit amplifier. Wish I had one. Great job on finding the cause. Cheers & 73 from W Rusty Lane K9POW in eastern Tennessee

[@TRXLab]

well, yes that is what you need...

[@dondonaldson1684]

Did you readjust the AFP trip point and make sure that the adjustnent pot wasn't intermittent?

[@Slartibartfas042]

Probably Scenario might have been: SMD multi-layer ceramic condensor dying for micro cracks by heat or maybe even from excessive voltage (maybe by VSWR misalignment?) and then being burned off in a few seconds at that rates could lead to excessive oscillation of your Amplifier. That would then lead to massive over voltages which then are sparking over and burning the massive hole into your PCB. Don't you think?

[@tomsmolcnop6358]

Irish Vikin

[@stevenandros4586]

Very enjoyable video (still watching it). The SWR detection circuitry is likely between the LPF and the antenna connector. In that location it is unable to protect the FET's in the event of a LPF failure. I have a pair of those FETs for sale should you want a spare. Cheers and 73 - Steve KG4LJB.

[@TRXLab]

Hi Steve, thanks for feed-back! All the best and 73

[@justinruth9729]

Wonderful amp quality

[@afshintorkamanzadeh9521]

Hello, it was an interesting video.. Do you remember the power MOSFET part numbers?

[@TRXLab]

MRF157

[@afshintorkamanzadeh9521]

@@TRXLab 🙏🙏🙏

[@trev9874]

I Have watched your video very good what software did you use to measure output power at the end thank you

[@nunolopes2885]

Peter, nice one again.Big thumbs up.Well that kind of pots are really bad, I've lot's of problems with them, since that I always use Bourns pots one critical circuits.The fault on the pot could be related to heat that it get's from the RF board, and with time it's gone deteriorate till complete failure.Again good job.

[@TRXLab]

Hi Nuno, thanks for feed-back. Well there are a lot of crappy pots on the market and the Bourns really first class but the used are already precision pots and not that bad. But the permanent heat is a problem to all components..Again thanks for watching 73

[@worroSfOretsevraH]

Nice video! I really would like to take a look inside that 1200W RFT dummy load. Thanks, 73.

[@TRXLab]

Hi, well there is really nothing exited to find only the full capsuled dummy and rough fans.. Thanks for watching 73

[@dixsusu]

SWR protection circuit was out of adjustment, great job and 73! YO5CAT

[@TRXLab]

Thanks for fed-back 73

[@OrbiterElectronics]

I always like to keep an eye on you my friend to see what you are up to :) Another great job Peter. Cheers John

[@TRXLab]

I'm always glad to see you here my friend! Thanks for watching Cheers

[@asz620]

Hello Peter!!!...Very nice work, I really enjoy watching your videos!!!

[@martinda7446]

Absolutely wonderful, entertaining and delightful. Glad to be a subscriber.

[@TRXLab]

Thanks for the kind feed-back Mart! 73

[@sputzelein]

Very good explanations. Networkanalyzer: would be interesting to know what komponents you need for it.

[@TRXLab]

Hi, thank you! You find all about the network-analyser in video #77. 73's

[@Dennis_Heaton]

Great explanations and good job on the troubleshooting.

[@TRXLab]

Thanks

[@Mrjm5411]

Enjoy you videos Peter. Would you consider a video on the Rhode & Schwarz CMT setup and use? Thank you!

[@TRXLab]

Hi, thanks for stopping by. Well yes hat video topic is already on the list only time is the issue.. Cheers.

[@herbertsusmann986]

Very nice video Peter. That is quite an interesting amp there. Almost looks homebrew, I guess it was homebrew in more than quantity 1?? Good that you could order a new board. I was thinking you would have to make your own! This kind of amp makes me a little nervous with so much power you can really do damage easily to very expensive parts. Vacuum tube amps are much more tolerant of abuse compared to MOSFETS!

[@TRXLab]

Hi Herbert, yes as I said at the beginning it is a semi professional PA and was build a couple of times. It is based on a Motorola application note for the mos fet's..That is the reason why you still get spare parts for it from the USA. Thanks for stopping by 73

[@JamesCutlervk2tim]

Those FETs are huge!

[@TRXLab]

and cost a bug of money

[@BVN-TEXAS]

@@TRXLabwhat model FETS are they ?

[@glaros0]

Dear Peter, I've really enjoyed this video, very instructional and well explained. I think I will see it again, I enjoyed it a lot. So, perhaps the cause of the problem was the setting of the variable resistor (51:49) that senses the reverse voltage level? Best, 73, Kostas

[@TRXLab]

Hi Kostas, glad that you like it and thanks for comment! Well the reverse swr voltage was the only finding after all that testing. But still it could has been a cold solder joint on the burned PCB as well but that we will never know.. All the best 73

[@subramanianr7206]

@@TRXLab but I am not convinced De VU2RZA

[@repairfreak]

Another interesting video viewed, great job as usual Peter.

[@iw0hex]

Another great lesson, thanks Peter. 73s de IW0HEX Pasquale

[@TRXLab]

Glad that you like it Pasquale. Thanks for stopping by 73

[@k5azebud988]

So, what do you think? The swr protection circuit was not working and therefore the current was excessive at the output transformer board? Did you happen to measure the temperature of the double binocular transformer, it looks a little small to me? This could always be modified to handle more load/heat if it was marginal. my guess would be the protection circuit did not engage when the band selector was not changed or set to the wrong band. You have some really nice equipment and I have never seen a dummy load like that one. Great job as always, 73...

[@subramanianr7206]

Correct. The amount of ferrite loaded in the transformer seems less maybe okay for a KW but not for handling 1.5KW. Using an infrared remote thermometer the temperature of the ferrite transformer can be measured easily. De VU2RZA

[@michaelrosenby3646]

Really a Nice video again. Thank you and best regards Peter

[@wadehicks9270]

You do great work Sir enjoy viewing your videos and learn a few things too. Thanks for sharing.

[@TRXLab]

Hi Wade, Thanks for watching. I'm glad that the videos are interesting to you. 73

[@Chipz0r]

One hell of a way to keep the shack warm. 73

[@TRXLab]

LOL yes that is right.. 73's

[@JamesP6084]

Very thorough testing very impressive Peter, as usual 73's VK6NJP

[@TRXLab]

Yeah a lot of work to make sure that the PA is working...Thanks for watching Jim 73

[@petechongy]

What was the 2 spurs at the sides of the carrier when you put power to the amp? 73s pete.

[@PapasDino]

Nice fix Peter. Even though the PA voltage is ~50VDC did the builder include a safety interlock? I'm used to working on my venerable Drake L-4B tube amp and cringe at seeing a open amp like that just from my experience! ;-) What did you end up setting the SWR threshold at for kicking the amp out of line? It's interesting to note that there was no apparent damage to the pot(s) in the sensing circuit and ever more interesting that one could have changed value sufficiently to allow the amp to operate into a high SWR condition and thus the over-current situation. I'll bet the moment it blew was exciting! 73 - Dino KL0S

[@TRXLab]

Hi Dino, no the builder did not include a safety interlock but with 50VDC I'm not really scarred. You still have to take care fore sure as you don't want to touch RF with 1,5KW but it is different to tube PA's with up to 5KV circuits...I set the swr threshold to 2,5:1 and cross fingers that there is not an additional hidden fault which didn't show after all testing. Yeah it is always the problem with semi professional devices as you can't really check the values against production values. The pot for itself was working okay on ohm test without any drop over the range. I was not present when the amp blew but what I have heard it was somewhat frightening...Thanks for stopping by 73

[@dinosworkshop6870]

Very concise and very detailed. A terrific video !!!!!!!!!!!!

[@TRXLab]

Hi, glad to see you!! Hope you are okay. Thanks for watching and comment 73

[@wab1954]

Great video!! Maybe I missed it but did you check the SWR protection circuit after you repaired the amp?

[@TRXLab]

Hi, no you don't missed it, I have done it off camera it is set to approx 2,5:1. Let see how it works. Thanks for watching 73

[@RC-Heli835]

This is spectacular!👍😃

[@k1mgy]

fantastic repair. however, are you absolutely certain that the cause was that swr protection circuit adjustment? why would this potentiometer be so incorrectly adjusted before you changed it? are you certain that your new potentiometer adjustment is correct? it seems you turned it to a maximum setting... should it not be designed to set near the middle of the adjustment range normally? this suggests that you may have compensated for a still-faulty protection circuit. ..maybe?

[@TRXLab]

Hi Mark, no I'm absolutely not certain but it is the only finding after all this tests. Why was it incorrectly adjusted? Well this is no industrial made PA and I don't know the quality standards the person who build this PA was using. So we need to take all into account..For now I adjusted the pot to a very sensitive setting may be we need to fine tune it but better than the other way around. Thanks for watching 73

[@israelhershkovits5675]

Man comeon just respaction!!!! After all best and proffetionall show.

[@GaryLordsWayMinistry]

I think the guy who ran the amp lost his antenna and threw the match out of the final stage of the transmitter's load network to the antenna and it fried the final stage of the transformer PI circuit when it got out of tune when the antenna went up in smoke. So we found that the swr protection section didn't work properly to cut power off to the output section of the power to the finals due to a bad pot trimmer. But what caused the high SWR to begin with the operator most likely. Not selecting the right band for operating of the band of output of the radio.

[@Mr.Laidukas]

Hi, nice video! Question - where from did you get that new board for such old PA? Where from did you knew what bias current must be?

[@TRXLab]

Hi, as I said in the video the PA is based on a application note from Motorola, there you find he suggested Bias. Parts can still purchased here www.communication-concepts.com/ar347/ Hope that helps . Thanks for watching 73

[@K1ZEK]

Enjoy your videos and this one was no exception. I read through the Q&As of others and now have no questions. Good job 73 Leo K1ZEK

[@TRXLab]

Thank you Leo! 73

[@izzzzzz6]

you could scroll around the 12M band to see where exactly that filter is tuned and then possibly re-tune it.

[@sdgelectronics]

That's quite a burnout on that PCB!

[@TRXLab]

Hi Steve, yes with a lot of smoke :-) Happy that the expensive transistors survived.. Thanks for stopping by. Cheers

[@jonka1]

I didn't see if you adjusted the SWR protection circuit with high power. Did you leave it at the sensitive setting from earlier?

[@andrewrae2813]

Excellent video as usual. This channel recommended by Mr. Carlson's Lab.

[@TRXLab]

Hi Andrew thanks for watching and feed-back. Paul is a very nice person!! All the best Cheers

[@19ac471]

hallo peter, ich habe jetzt einen eintrap in meinem besitz. Haben Sie vielleicht weitere Informationen zu dieser Endstufe? Ich würde gerne wissen, wie hoch die maximale Leistungsaufnahme ist. und ist es gegen zu viel eingang und hohes swr geschützt. bvd Stefan PD5S

[@GiorgioFirpo_IU1BKT]

Very interesting your "network analyzer". Can you explain something more about ? Where is possible to find it ? Many thanks Peter. Very dangerous video too. One distraction and you blow away all your laboratory in one shoot. :) :)

[@TRXLab]

Hi Giorgio, thanks you for feed-back. Yes if you are working with transistors like this you have a bad feeling as you can loose money with one shoot... The network analyser is a Signal Hound. You find all about it in video #77 . Cheers

[@GiorgioFirpo_IU1BKT]

Thanks Peter, very kind.

[@technos123]

Great repair. All that power output would make me real nervous though.

[@TRXLab]

LOL no fears here.. Thanks for watching 73

[@bloguetronica]

Is it possible that the damage was caused by an arc? I suspect that because of the hole in the PCB, and it's placement between power planes. An arc could have started there, carbonized the PCB, which led to further conduction and heating.

[@subramanianr7206]

I don't think so De VU2RZA

[@andrewandrosow4797]

1206 and bigger capacitors were often short-circuit in my hobby devices - i suppose, it was because I don`t have an infrared soldering station. 4:14.

[@Gw0wvl]

This is why i prefer Valves to High power transistors, For instance The cost of a GS-35 valve is a fraction of the cost of a high power transistor and a lot more forgiving...... Great video , But Ide take a high power valve over a transistor anyday :-)

[@TRXLab]

Yes you are right valves are a lot more forgiving... Thanks for watching and comment 73

[@Gw0wvl]

Its my pleasure, I always watch your videos, Your knowledge is superb... Thankyou..De Gw0wvl ... 73

[@carlosotaviodasil]

É bonito ver um verdadeiro técnico!!

[@TRXLab]

Thank you 73

[@kevingray707]

What is the software and h it you are using in the video. It is so awesome

[@TRXLab]

Hi Kevin, I'm not sure what you mena. I'm using a signal hound spectrum analyser in this video. To get more information on it watch video #77 All the best 73

[@magicwoody]

schönes Output Signal.. sehr nice 73

[@bobwalter53]

HI. Do you think you could do a video step by step on how to make the right bias adjustments to the Yaesu FT-991. What bridge to remove ect. Thank you,

[@TRXLab]

Hi Bob, Bias adjustment is always the same procedure.. I have an older video on-line. Watch video #34 and additional to that I show the procedure in video #88. Hope that helps 73

[@berndb.5097]

Hi Peter, verry nice video and a high Q repair :-) What did you at least with the AFP circuit? Was it enough to set it to a higher sensitivity? 73 Bernd

[@TRXLab]

Hi Bernd, yes as first step I have set it to 2,5:1. Now lets cross fingers that there is not additional a hidden fault 73

[@ezio_g]

Very impressive work.

[@hornsby5533]

RFT KAM-1300 does a good job. 😁

[@RC-SUB]

How many input power was used for 800 Watt ? THX Andy

[@TRXLab]

Can't remember anymore, but I believe it was between 10 and 20 watt

[@douro20]

Can this transmitter handle being keyed down around the clock?

[@eduardosomoanocrematy7802]

Dear friend forgive the daring to write to him on his channel but I would like your opinion technique of the problem of my Yaesu FT-450. Here I explain what happens with my Yaesu FT-450. A few days ago I made the mistake of trying a radio from a friend of mine when my FT-450 was on receiving, they had two different antennas but the separation between the antennas on the roof are 3 meters. When I was testing the radio in transmission I felt a burning smell from my friend and I realized that it was coming from my radio, at the moment I turned it off and when I turned it back on it had changed many things like: - TRANSMIT BUT DOES NOT GIVE ANY OUT POWER IN (AM) MODE ON ANY BAND. - THE SYSTEM (ALC) DOESN'T WORK, NEVER MARK ANYTHING ON THE DISPLAY, BEFORE IT WORKED VERY GOOD. - ESPECIALLY IN 6M (50MHZ) BEFORE HAD 100 WATT, NOW ONLY HAS 10WATT AND WHEN CW OR SSB TRANSFER FEELS MY VOICE OR NOISE IN THE RADIO HORN. - THE INTERNAL RADIO TUNER ANTENNA DOES NOT ADJUST IN SOME BANDS AND HIGH SWR WITH GHOST ANTENNA DUMMY 50OHM ADJUST 1: 1 ALMOST ALL BANDS, I REMOVED THE RADIO TUNER ANTENNA AND CONTINUES WITH THE SAME PROBLEM, THE PROBLEM IS NOT THE INT-TUNER OF THE FT-450. - BEFORE ALMOST ALL BANDS DRAWN 100 WATT CW AND ALMOST 90 WATT SSB. NOW HIM RESULT WITH LOAD DUMMY 50OHM PER BAND IS: 160m ... fm .... 100 watt cw .... 100 watt am .... no carrier no power fonia and digital .. 100 watt ----------------------------- 80m ... fm .... 100 watt cw .... 100 watt am .... no carrier no power fonia and dgital .. 100 watt ----------------------- 40m .... fm .... 70 watt cw .... 70 watt am .... no carrier no power fonia and digital ..40 watt ----------------------- 30m ....... fm .... 70 watt cw .... 70 watt am .... no carrier no power ----------------------- 20m ....... fm .... 70 watt cw .... 70 watt am .... no carrier no power fonia and digital .. 40 watt ----------------------- 17m ....... fm .... 50 watt cw .... 50 watt am .... no carrier no power fonia and digital .. 30 watt ------------------------ 15 m ........ fm .... 80 watt cw .... 80 watt am .... no carrier no power fonia and digital .. 80 watt ------------------------- 12m ......... fm .... 80 watt cw .... 80 watt am .... no carrier no power fonia and digital .. 50 watt When I transmit on the phone you can hear it on the radio horn ------------------------- 10m ......... fm .... 50 watt cw .... 50 watt am .... 10watt fonia and digital .. 50 watt --------------------------- 6m ......... fm .... 20 watt cw .... 20 watt am .... 20 watt fonia and digital .. 20 watt, When I transmit in fonia it is heard in the radio horn. He also seems to be crazy, he makes noise and he seems to have serious problems. I RESET HOME OF THE RADIO AND CONTINUE WITH THE SAME PROBLEM, THE PARAMETERS THE HIDDEN MENU IS CORRECT, THE RECEPTION IS CONSIDERED GOOD IN ALL THE BANDS AND MODES. I CHECK THE BOARDS OR BOARDS AND ALL ARE IN GOOD PHYSICAL CONDITION, NONE COMPONENT SEEMS TO BE BURNED. BEFORE MAKING THE ERROR MY RADIO WAS WORKING NO PROBLEM WITH 100 WATT IN ALL THE BANDS AND THE AUT INT ALSO WORKED NO PROBLEM. I HOPE THAT WITH THESE DATA YOU CAN GIVE ME AN IDEA OR OPINION OF WHAT PROBLEM THE TEAM HAS THOUSAND THANKS IN ADVANCE. note :Now I have realized that when I press the ATT or IPO key that is only for reception it falls even more the power in all the bands, in addition I tested it in reception 6m 50mhz and it has problems also at the reception . BEST 73.- EDUARDO CO8LY