70 Watt Amplifier Kit Build

[@DesertRatLife]

Those moments when you see a random ebay item and hope someone on youtube hs already purchased and reviewed and when you check sure enough someone has. Thanks for taking the time and details of this video. cheers.

[@na5y]

Thank you!

[@johnwest7993]

As is, this is a pretty junky amp with a whole lot of thoughtful work required to get it right, and the power output is often wildly exaggerated by vendors, so I'm glad you are going through it to point out all of its shortcomings and how to fix them. What it is is the start of a decent little power amp for a very low price, (when it's not being outrageously exaggerated by eBay vendors.) What they require is some additional good engineering work, which you are putting into them so that other hams can reproduce it with theirs. Thank you.

[@draganjovanovic7104]

Hello NA5Y, You helped me to find where I made a mistake with Your checking the continuity between the parts. I am new in "Hobby" so I soldered the small transformer to the board like I am "welding a stairs to the house" 🤣and bypassed, connect it to the ground (-) but Your Beep Beep was very very helpful. Hope the whole thing will work after I finish it again. Thank You so much. Best regards, Dragan, Belgrade, Serbia, YU4ELD 😀

[@na5y]

Glad to have helped Dragan. Thank you very much for the comment!

[@johnlannigan9831]

At 17:40 you mentioned the space for a resistor which isnt fitted, there is a simple explanation. This PA board is universal for both the 70 watt version (Minipa70) and the 100 watt version (Minipa100). In the 100 watt version the two IRF530's are replaced with a dual Mosfet package the MRF9120 and this is when this resistor is used. Its a simple matter to upgrade the 70 watt PA to the 100 watt by replacing the two IRF530's with the single MRF9120 dual device and adding this resistor.

[@na5y]

Thank you John for the comment. I did also notice that even with the IRF530s a correctly chosen R6 can improve the input SWR. Sorry for the delayed response - your comment only just appeared for me.

[@m1geo]

R6 is for reducing the input Q. Flattens out the frequency response. 😁

[@falandoareal4578]

Esse é 1 amplificador para 40 metros ? Valeu 👍 obrigado e parabéns pelo projeto ! Top d+

[@na5y]

Sim, este amplificador é para 40 metros. Que bom que você gostou do vídeo

[@SCTV59]

Excellent presentation. I plan to build the 45w version for a usdx+ 5w hf transceiver. Hoping for 25w output. Thanks for posting.

[@na5y]

Thank you for your kind words

[@Adui13]

I bought this one for the uSDX+

[@gammaleader96]

This is acutally a pretty nice little kit. I got one with the reused 880MHz LDMOS transistor (they are sold as the 100W version). I think they are a great way of getting into amplifiers and good for experimenting.

[@na5y]

I agree - simple to understand and build. Those two links I provided (dk9jc and pa11019) had some great additional content - do check the out. Thank you for the comment!

[@m1geo]

R6 is a de-Qing resistor. It reduces the peaky nature of the input matching.

[@drvigg9083]

Very nice video. I do wonder, however, about three things that I wish you had touched on: 1) What bias voltage did you use, and how did you decide on it? 2) Signal looks great on scope, but that's after it was cleaned up by your low-pass filter. What's it look like without the LPF? 3) Output power looks good at 7MHz, but what is it like on the high bands?

[@na5y]

Hi Doc. I did a followup video that answers some of yout questions: kzbin.info/www/bejne/kKenoaN4hNubqqs In a nutshell 1) I settled on around 3.3V which was significantly higher than the 2.8V max you can get with that bias resistor in there (I removed R7 and speak about the mods in the followup video at 8:44) 2) Signal looked pretty good even without LPF - definitely still some harmonics there though 3) I didn't get around to testing on the other bands unfortunately I do plan to play around with this amp in the future - thank you for the comments!

[@Adam-SP5AWL]

You are lucky. I got this board with SMD parts not soldered.

[@na5y]

Its quite random. I ordered one *without* the SMD parts soldered and they came soldered!

[@Adam-SP5AWL]

@@na5y Of course they delivered parts in the bag without a manual. Do you have any?

[@na5y]

@@Adam-SP5AWL Have a look at the video description. There are all the links I found including a schematic. There's no manual for the kit I have found

[@Tocsin-Bang]

Having blown up my main transceiver, I've been thinking of getting one of these to go with my uSDX+, looks just the job.

[@na5y]

Good luck Stephen - the amp requires 5W driver if I recall correctly - not sure what the uSDX outputs.

[@Tocsin-Bang]

@@na5y depends on band, mine gives 3.5-5 watts, lowest output being 10 metres.

[@linkmaticelectronicspakist4693]

Nice video. by the way this amplifier also works on SSB i have personally tested it so no issue on SSB yes if you add a Low Pass filter then it works great.

[@m1geo]

I'd be interested in seeing a two-tone test for linearity. Maybe increasing the bias current would help.

[@na5y]

I did do a followup two tone test here: kzbin.info/www/bejne/kKenoaN4hNubqqs

[@MakeDoAndMend1]

Mine had Resistor R6 missing from kit. Also it's not shown on circuit diagram. When R6 is fitted it greatly improves SWR at tranceiver to amplifier. Cheers from old George

[@na5y]

I don't think R6 comes with any of the kits. I guess they don't supply it because it is somewhat band specific. Thanks for the comment George!

[@curtstacy779]

That signal looked nice. you should check it on your spectrum analyzer. I bet it would be fine on the air. it would be fine for AM or FM. if you use the port on the radio to key it witch it looks like you are, you may not need to make a delay for SSB if the radio provides that. Looks like a fun project. Thanks.

[@na5y]

Thank you for the comment Curt. I did check the harmonics on the simple FFT function on the oscilloscope and the highest harmonic was at 21Mhz - 35dB down. Unfortunately this amp doesn't have great linear behavior. I might do some tests showing that!

[@curtstacy779]

@@na5y Aww that is to bad, but on a brighter note I've heard there is another Mosfet you can use on those that performs well with higher band width and less harmonics. maybe something to play with. (RD16HFF1).

[@na5y]

I have some genuine RD16s out there - might try that. The pinout is different though (GDS for IRF, GSD for RD16)

[@curtstacy779]

@@na5y That would be great to see the difference. or whatever else you decide, because you make some nice videos.

[@U812-k7j]

Are the tabs on the IRF530's insulated from the heatsink? Looks like the screws have insulating bushings

[@na5y]

Yes they are - there's a little SIL pad under each

[@martincvitkovich724]

I bought a old Heathkit GW-12 CB Base at the Dayton Hamvention. I built one of those back when I was a kid in the 60's so I couldn't pass it up. The radio works good but I can only get less than 1 watt and according to my meter, it is around 1/2 watt, so I am looking for a amp that will boost the output on the cheap. Will this kit work for the 11 meter? Would it be a straight forward build, with instructions?

[@na5y]

It'll work on 11 meters with an appropriate low pass filter - which is not included. I haven't tested it there. As far as instructions go - the kit comes with *no* instructions whatsoever. Also - you will need a heatsink - as that isn't supplied either. Good luck with your build and thank you for the comment Martin!

[@roberth5435]

In short, the supplier does the easy stuff, the pick-and-place and oven-solder of the SMDs. You have the labor-intensive tasks of building all the inductors and mounting all the through-hole devices. This kit has the advantage of new IRF530PBFs, unlike the recycled components of other kits. You'll have to provide your own low-pass filter and power supply.

[@na5y]

Indeed - although I view the labor intensive parts as the "fun". Thank you for the comment Robert!

[@CKJEntertainmentServ]

of all the few videos i have found for this, you have the BEST video! but i wonder if i may ask.... i built my little amplifier to your instructions, however, i do not have a oscilloscope, and i dont have the low pass filter yet, but i tried to test wattage with just my wattmeter, and i have zero output. i can key my radio with 1 watt, and it registers on my watt meter, but as soon as i key the amp, i lose the 1 watt that i have, as if its not putting out. can you suggest where i might look to see if i have something wrong? i did adjust the bias to approx 2.7vdc as some schematics have shown it to be. thanks in advance for your help. this is my first kit, and am excited to see it work!

[@na5y]

Thank you. Remote troubleshooting is super tough. Some things to check 1) Low pass filter is certainly needed to be on air - but isn't needed for testing 2) Is the output of the amp going to a proper 50 ohm load? It really should - and in testing it should be a dummy load 3) What is the current draw from the amp during transmit. If it is low then you may have blown FETs - check them. 4) This is super tough to check without an oscilloscope but you really have to see whats going on at the gate of the FETs. Are you getting a properly biased waveform? Not sure how you'd check that with a multimeter though. 5) I know its a bunch of expense - but consider getting a cheap oscilloscope. You don't need an expensive one at these frequencies - and it opens up a whole pile of diagnostics. Something like this perhaps (no affiliation) www.amazon.com/Siglent-Technologies-SDS1052DL-Digital-Oscilloscope/dp/B01J16NV54/ref=sr_1_4?sr=8-4

[@ericzerkle8486]

I wish someone would do a review to the 180w version.

[@exgenica]

What electrical function do the "ferrite tube" bushings perform (if any)? Do they just more securely hold in place the ferrite tubes? If that's all they do couldn't one just use some RTV silicone to lock them in place once the wiring through them is completed? edit to add: I'm just trying to make sure I'm not missing some finer point of this design. I like to design for "what ifs?" and it's a lot easier to snip off some silicone than unsolder the bushings if for some reason I end up accidentally breaking a ferrite tube and have to replace it.

[@na5y]

The certainly hold the tubes in place but the bushings main function is to act as one of the electrical windings in the transformer. The other winding is the actual wires going through the bushing.

[@exgenica]

@@na5y Thanks!

[@Adui13]

Any chance you would be willing to do an updated video building one of the Amazon versions that the SMD's are not already mounted? I have the kit(I knew what iwas getting into) and I want to build it right, but mine came with a bare board and a bunch of SMD components.

[@na5y]

Yes I think I'll try that out! Stay tuned

[@NeedleBender785]

Great video. I was actually thinking of picking up this kit for my home brew super-het radio that I am building. Still really curious about what you said at the end of the video about SSB and overall linearity. Just curious if you had time to run a test with an SSB signal on it? Thanks

[@na5y]

Thank you for the comment. I think I was a little hasty claiming this amp would be no good for SSB - I have seen some more videos where the amp was being run with acceptable linearity. I am definitely going to be doing some more testing and will publish the results

[@NeedleBender785]

@@na5y Awesome! I was actually surprised also to see how clean the sine wave looked on the scope. Very little high frequency components in there. Would be cool also to see it on the spectrum analyzer without any LPF installed.

[@na5y]

Without the LPF it looked pretty much like a square wave! I should have recorded it but the video was getting a bit long - I can add tha to the followup!

[@NeedleBender785]

@@na5y Oh! Wow. I thought that was without any filtering.

[@Francois_Dupont]

@@na5y i dont have a spectrum analyser like you. could you give a link to your LPF? i am mainly looking at 20m-40m. i had a look at the other guy website your linked. he has alot of shematics, but it is not written on them witch band is witch part of the circuit.

[@malchaschwatrz5706]

I blew the irf 530s...Will check the bias circuitry to make sure it is ok after removing the mosfets. I have irf 540s.Do you think they will work as well as the irf 530s...I overheated the irf530s .They were working well until I got too talkative on SSB! Thanks...

[@lovelycollection100]

Y es this work un 40m

[@k.c.sunshine1934]

It would seem that 7 MHz operation could benefit with 48 AWG times 675 strands of litz wire on the binocular core and tube cores?

[@na5y]

I have never tried litz wire (I had to look up what it is ;) ) - do you have any references you could share ?

[@k.c.sunshine1934]

@@na5y the idea is that of "skin effect." At DC, the full conduction of the full diameter of the wire occurs. At higher frequency, the effective conduction is limited to a "skin" of conduction. In order to mitigate skin effect, one may use multiple strands of insulated wire that has an equivalent diameter of what is needed. Hence "litz" wire. Litz is great to increase the "Q" of filters, etc. The potential drawback is that its use may make the circuit less stable.

[@skylabby]

I would have actually liked to see the winding process of the xformers, but thanks for another great video.

[@na5y]

Are you interested in terms of how you count windings through a binocular core? I think I did do a video on that a while back - let me check!

[@martincvitkovich724]

Just recieved the 'kit'. Since there is no instrutions , I am going to follow your video. It may take me month to put this together, as I will need the heat sink and a new soldering iron. Also the input and output for coax is so small, I never seen connectors smaller than the BNC on VHF gear. What are they called?

[@na5y]

Good luck with the build Martin. The small connectors are SMA - specifically female PCB mount SMA

[@lawrence1md]

Have you done a 144mhz version?

[@na5y]

I haven't Lawrence but that might be fun to do...

[@lawrence1md]

@@na5y I’ve been looking for one but I must not have the right word combo for the search to find it. Great video by the way.

[@na5y]

@@lawrence1md Here's one on ebay. No idea at all how good it is. Search using the following: "100W FM VHF 80Mhz-170Mhz RF Power Amplifier Board"

[@lawrence1md]

@@na5y I did find on similar to that one. It uses a 24-26 volt power. Some do not come with the transistor or it’s used. I’m going to keep looking. Thanks for looking too!

[@davem6492]

Can you test it without a lowpass filter? if so how ?

[@na5y]

Testing on the air should never be done without a filter. You can test in the workshop without a filter just put your 50 ohm dummy load on the output. There will be a lot of harmonics

[@cthoadmin7458]

So what would you have to do to improve it's linearity to make it suitable for HF SSB? What's normally done?

[@na5y]

I think the only way would be to replace the IRF with a FET more suited to HF operation - like the RDHF series

[@gnosticcommunications8933]

Mine exhibits a lot of harmonic output in the absence of an output LPF, which is needed before puttiong this unit on the air. The manufacturer also states that it must be protected from any accidental output open circuit or short circuit load and will only work into a maximum SWR of 2.0:1. I have an output load out-of-range detector and shutdown circuit, which I designed and built myself. This circuit of mine will both ground this amplifier's bias line (to zero volts) and inhibit exciter transmit power being applied by disabling PTT when the output load is out-of-range; open, short, or SWR greater than 2.0:1. One diifficulty I had with this amplifier's PCB is there is insufficient clearance between the PC trace for the center tap of the secondary side of the input ferrite RF transformer and an adjacent swath of ground. This can result in an evasive intermitten short to ground on the center tap of the secondary side of the input ferrite RF transformer, which kills the bias to the power FET gates.

[@na5y]

Thanks for the comment. You definitely will need an LPF - no question on the output. I didn't have any output protection but I have seen other experimenters do as you did. On the last point do you have a picture - I didn't have any problem like that on my board - there seemed plenty of space but I am not quite sure where you are referring to

[@gnosticcommunications8933]

It is well concealed under the solder mask. There is a sizable swath of PC copper that the end caps of the input ferrite transformer solder down to. It is the opposite side of the transformer from the FET gate inputs. R3 and C3 connect to it as I recall. Anyhow that sizable swath of copper that the transform,er end caps solder two is exceedingly close to a parrallel swath of ground copper. I had to remove R3 and C3 and the bias adjusting potientometer to find the issuer,. which is under the solder mask. I then widened the gap with an X-acto kinfe.@@na5y

[@mvssarma3387]

I suppose better to add a 1uH inductor inserirs to feed back to make rcl instead of rc . This would improve linearity of the amplifier. Sarma vu3zmv

[@cisco40ty]

Would this kit be good for CB radio? Want to make something small for my truck for when I am in only in the mountain.

[@na5y]

I wouldn't want to say anything that would get me into trouble with the FCC but this amp will work on 10 meters with an appropriate low pass filter on output. You won't get anywhere near 70 watts though on SSB or AM - maybe 30 watts perhaps 40.

[@ic7481]

Why do you have the 20MHz bandwidth limit actived on your scope?

[@na5y]

Just to cut down noise on the waveform is all

[@alanwhitcombe5358]

sorry im kinda stuck on this one i gor rig of the irf530 and i did get a MRF120 now im finding it hard to work out what resister goes in R6 place

[@na5y]

Have a look here for the values at different frequencies pa-11019.blogspot.com/2016/11/diy-kits-70w-ssb-linear-hf-power.html Those were arrived at experimentally so you might have to play around a bit. The resistors do need to be at least 3W

[@rickmckee6698]

I'm wondering if the kit comes with full instructions and where can I get one ?

[@na5y]

I got mine off ebay - the link is in the video description above. It comes with no instructions whatsoever

[@foxman362]

1:02 Where can i find those blue things at i only got one blue thing in the mail today it didn't came with two.

[@na5y]

Sure - they are 100 ohm 3 watt resistors. Amazon has them here - unfortunately you have to buy 40 www.amazon.com/Fielect-Tolerance-Metal-Oxide-Resistors/dp/B083TGGKNT/ref=sr_1_12?crid=VKDDBMIRI86Q&keywords=100+ohm+3+watt+resistor&qid=1653146552&sprefix=100+ohm+3+watt+resistor%2Caps%2C476&sr=8-12

[@МКпрограммирование]

How you soldering electrolytic C2 near T2 transformer? And how define bias current transistors?

[@na5y]

For C2 I put a little blob of solder on the pad closest to the transformer and then I have a very fine angled soldering iron tip that allows access to tack the cap down. Of course I should have installed the caps first - that would have been easier. As far as bias goes I started with a bias of around 2.8V and carefully increased it to around 3.3-3.5V. You do have to be careful here as there is no thermal protection and those IRF530s blow in an instant. Thank you for the comment - I hope this helps

[@Francois_Dupont]

put some fresh solder on the PCB pads and some on the capacitor leads. then press the two in place and heat them up the best you can.

[@deveshsuroshi]

You mentioned this will not work well on SSB, is there anything to correct that? just ordered the board. 73s

[@na5y]

It will certainly work on SSB - you won't get anywhere near 70 watts out of the amplifier though. I do a follow up two-tone test with the amplifier in a later video: kzbin.info/www/bejne/kKenoaN4hNubqqs

[@deveshsuroshi]

@@na5y Thank you so much, will look into it too!

[@N2AIE]

quick question RE: Bias adjust test, I can read from zero to 4.8vdc..didn't think it should go that high (13.8vdc in) comment?

[@na5y]

That does sound a little higher than the max I had but I can't recall exactly what that was. Did you short out resistor R7 like I did? That does give a greater range to the bias. The pain with the bias adjust pot is there is no defined "start" and "finish" - it just rotates freely which means you can go from 0V to maximum with a tiny adjustment. In any event you don't want to go much higher than 3.2V (even that is pushing it)

[@N2AIE]

@@na5y no didn't short out R7, so I'll just have to be careful. Don't even need the 50w out, intending to integrate amp with either a QCX or an old uBitx..

[@N2AIE]

Just getting back to the build. I have a couple of smaller heat sinks, just wondering how smaller than you had to be in a safe zone, and plan to use forced air (fan)..Comments?

[@na5y]

@@N2AIE I used a quite large (3in x 4in perhaps) heatsink and I think that would be enough for intermittent work. Definitely need a fan and a way of monitoring heat for more sustained work. I do plan on getting back to this amp myself soon (hopefully)

[@prizeking1647]

Is there anything I can do to stop the 2 resistors getting extremely hot ?

[@na5y]

If you have them mounted close to the board you can mount them higher so there's an approx 5mm air gap. This amp probably needs a fan to be honest

[@taki8592]

I've burned two sets of irf530's so far. Thanks for the video. I have lowered the bias to 0 V and will strart gradually from there. 73 de Z33ST

[@na5y]

Yeah - those IRF530s go quickly., even when well heatsinked

[@MakeDoAndMend1]

Manual says 2.7V but 3.2 is best. Make sure you have R6 installed.

[@na5y]

@@MakeDoAndMend1 agree to both! I even took it up to 3.4V. Thank you for the comment

[@lovelycollection100]

Need 50ma vías irf are diferent

[@allanjaypalomique7609]

is that amplifier a fm frequncy sir???

[@na5y]

The amplifier is a linear amplifier - so it can amplify AM and SSB signals without (too much) distortion. It can also amplify FM

[@ObamaoZedong]

English version please?

[@na5y]

Some may disagree but I am pretty sure Australian counts as English... ;)

[@logicman91]

Can irf3710 be used for this

[@na5y]

The rise + fall time of that mosfet is around 100ns - I would say it might be too slow for HF work.

[@logicman91]

@@na5y i put some in i cant test completely need a heat sink i have been able to get 22 watts out with 6 watts in been going through circuit in original configuration had a bunch of bad components. I dont expect to achieve much here performance was better with 530 at 1.8 vdc bias these 3710s at 3.13 can get it higher at the moment

[@frankywatte5646]

I'm confused, I thought the formula for power calculation is P = U²/R ? There is 140vpp on the scope, which makes 140/2=70V²/50 ohm = 98Watt ???.

[@na5y]

Hi Franky. That is the correct formula - but the "V" in that is the RMS voltage - not the peak voltage. For a sine wave To convert from peak to RMS voltage you divide by sqrt(2). Heres a useful reference: www.analog.com/en/analog-dialogue/raqs/raq-issue-177.html Thank you for the comment!

[@frankywatte5646]

@@na5y Thanks for the explanation, I learn something every day.

[@alanwhitcombe5358]

hi my msd caps the pin came off so i have replaced with the normal cap with the black heat shrink over them should that matter? i do have the msd soldering gear but for some items its the soldering iron and very fine tip, im also hunting down some bare bords only. why im ino cb and im a it tech repair man im not a spring chicken i have just turnd 50 on 4yh july

[@na5y]

Hi Alan - you'll be fine with a standard electrolytic in place of the SMD - just make sure polarity and voltage are good. I haven't seen the bare boards for sale - although have a look at this video where I made my own. kzbin.info/www/bejne/fXbbqHSQqdl5l5o

[@alanwhitcombe5358]

@@na5y hi i have it all built now. what els do i need to to before i connect to my Washington but i will take power down to 5 wts on the radio. why that rig i want to convert it to 27mhz as its on the ghost band at mo yes 26mhz is so nice and silent all the turkys went uhf. us nice bugers are on 27mhz unless some nice ham comes to 27 and wants us to see how good he/she comes to nz with sig test. yes i do that a bit but i only tell them the sig and how good it is and we get a big thank you and flic my numbers then bugger off. then i head back to 38 or 35. that out of the way what do i have to buy now for it to work on 27mhz i have a the amps to run it i just take my benchtop 40 amps and that was running my anytone 5555n i just hope my ten amp will now run the anytone rig. if i have to buy xtras do you sell them? thanks Alan 41KK407 you can get me on 38 when states side at night and we are day as yes we are getting usa skip most days cheers and 73's ps i will get my has tic i just want to get my gear sorted my main rig is 25-30mhz and i also have a baofeng handheld thats unlocked not like the new locked radios. 73's

[@alanwhitcombe5358]

@@na5y what els do i need for the amp ? i also built my self one of those auto swr units and made a rechargeable battery packs so if im out and about i can tune any antenna i can run on 26 and 27mhz but the kit says 1 to 50mhz and upto 100wts even thou my setup is 1:1 the dam needle dont even move on 27mhz but 30 mhz wow my needle crashes to other side of swr meter but stick on the auto swr tune it goes way back to 1:1 any ways 73's and im off to sleep its 11:37pm nz time..... at some stage it will get upgraded to a 140 wts chip then buy one at a time to about ten then join the up as one missive amp . then work out a way to convert ac mains to dc it will either work or have a missive blast go off

[@na5y]

Where it gets tricky is you also need a low pass filter after the amp to remove unwanted harmonics. There are LPFs you can get on eBay for your frequency of operation. The other thing to be mindful of is this amp certainly won't put out anywhere near 70 watts. The best you'd get is around 30-40W and even then you'd likely get splatter. I hope this helps and thank you for the comment

[@alanwhitcombe5358]

@@na5y thank you now thing is i have my radio that i will turn it down by 4 wts then i have my auto antenna tuner then amp the lpf what way should they be thanks

[@jfrphoto01]

Can anyone supply me with the value of VR1? My kit is missing that part.

[@na5y]

Its a 1.5k linear

[@jfrphoto01]

@@na5y Thank you! Excellent video!

[@Aron102]

Nice video, love these kits all good fun 👍 subscribed

[@na5y]

Thank you Aron - glad you enjoyed!

[@Aron102]

@@na5y yes very much enjoyed I know it’s not easy to make These videos, so thanks for sharing. Please check out mine not as good of yours.

[@GeorgeWMays]

Thank you for a fun video. It's appreciated. 73s....

[@na5y]

Thank you George!

[@VU3ZNL]

CAN I TRANSMIT WITHOUT LPF

[@na5y]

To transmit legally you need an LPF

[@VU3ZNL]

@@na5y In VU not required by law

[@na5y]

@@VU3ZNL I would be surprised if the India Dept of Telecomms doesn't have a similar rule.

[@VU3ZNL]

They say thath you should not interfeare with other singnal thath's it

[@na5y]

@@VU3ZNL Ah then if you don't put in an LPF you would potentially be interfering with another signal

[@Francois_Dupont]

could you tell me if it is normal for the completed amp not to draw much current nor heat up when turned ON, but no RF in? i am in the process of building one of these kits. as i am testing them before installing inside a case. the amp doesnt heat up when turned ON without any radio plugged in. i was under the impression that they would heat up and draw some power even in a idle state (turned ON, but not amplifying).

[@na5y]

Interesting question. By "no RF in" you mean that the PTT is also not activated? With no PTT those FETs aren't even conducting as grounding the PTT turns the voltage reg to the gates of the FETs on. In that case you should get no heating at all. If you have grounded PTT but no RF input then the FETs will be turned on to some extent but the quiescent current draw should be quite small - around 100 mA in this amp IIRC. SO you shouldn't get much increase in temp. Depends where you have the bias set.

[@Francois_Dupont]

@@na5y ok ok. my father and i both built the same kit. ours isnt drawing much with PTT active, but no RF in. strangely the board my father built appear to be working correctly, but my kit isnt. mine doesnt look to be fully amplifying. it is drawing only a little bit of power. i dont know if you have time to help me. i know diagnostic of random stranger on the internet is very annoying. the sine wave coming out (7mhz 40m band) looks to be perfectly normal, but the current drawn by the amp is too low. have you had a similar problem? 80m: 4.18A 60m: 3A 40m: 2A 30m: 1.3A 20m: 0.7A 15m: 0.4A 10m: 0.6A using various powersupply 12-13V including Li-Po battery capable of high current drain. i checked the voltage drop at the board and it is not a power supply issue.

[@Francois_Dupont]

i forgot to say, i am using 3.6~ volt Bias. i have tried to lower it down, but it doesnt seems to make much difference.

[@na5y]

Not annoying at all ;) What is the RF driver you are using for the amp? This amp needs at least a 1W RF driver (approx 20V peak-peak on input). At 40m, say, what is the peak-peak output of the sine wave. Is it stable? Another thing to check would be the windings on the final transformer. Make sure you have the correct number. Hope this gives you some leads. Let me know how you get on. Remote debugging is tough - but it'll be rewarding if we can get you working!

[@Francois_Dupont]

@@na5y i am using a uSDX+ (

[@Davidsmith218]

Could you replace the irf530 to a irf540

[@na5y]

You definitely could - pinout is identical. Bias would be different of course

[@Davidsmith218]

I received this amp had nothing but issues I followed every instruction from your video and as soon I applied power it was a short I used the supplied 530n transistor then order another set same issue ? Shuts my power supply down as soon as I apply power check all connections not sure what is going on must have received a bad board or one of the already attached components is shorted

[@na5y]

​@@Davidsmith218 DId you get a chance to measure the bias voltage? When the mosfets blow it usually produces a dead short between Drain and Source. When I was playing around with it I did manage to blow one of the traces on the board completely (the one between the final transformer and the drain) Some things to check 1) With the mostets still installed Check between the input side of the output transformer (those big pads) and ground. Should be no continuity 2) If there is remove both mosfets from the board and try again. If after removing there is no continuity that definitely means one or both of the mosfets is blown. If after removing the mosfets there is still continuity then maybe you have a solder bridge somewhere (or potentially the input side of the transformer is connected to the output side somehow). You have to fix that before proceeding. 3) If you have a component checker check both mosfets (if you don't you can use a DMM - refer here kzbin.info/www/bejne/nZ3Smp6mbtllmqM) 4) Before reinstalling the mosfets make sure you check the bias voltage at the gates of the mosfet - do this without an applied signal - it should be no more than around 2.5 V - but I would start at 0V and slowly work your way upwards. Incorrect bias voltage is most likely the reason if you are continually blowing mosfets. I hope the above gives you some leads - and remind yourself that debugging is always more than half the fun ;)

[@Davidsmith218]

Yes it works I didn't have any more 530n so replace with 540n and it was the Bias volts so set it to 2.5v driving it with 1 watt and getting 10watts out too scared to drive it any harder thanks for the help and information

[@Davidsmith218]

@@na5y I look at the data sheet and it shows 100v so is this the supply volts and the Bias volts of 4v max for the 540n so is it possible to separate the Bias circuit from and run the MOSFETs on a higher voltage I'm trying to get 120w to 150w my TS830s is tube and are weak I can get 5-10 watts out from the ts830s and would this amp possibly work for SSB I'm in the process in building a keying circuit to key the amp I rewound the output binocular with 5 turns instead of 3

[@stevew9945]

kicad link is broken

[@na5y]

Try again - I had set the repo to private incorrectly

[@radiotec76]

Fascinating video! With proper biasing couldn’t this irf-530 pair be run class A/B?

[@na5y]

I would definitely think you could run this with a pair of IRF510s. Less power of course - thank you for the comment!

[@radiotec76]

@@na5y sorry, I meant to write irf-530 not irf-510. Still, with the right bias voltage, class AB is possible.

[@na5y]

@@radiotec76 I think you are right - I have now seen others who have been able to make this work AB. Definitely want to do a followup video on that

[@radiotec76]

I look forward to it complete with oscilloscope 2 tone generator porn.

[@berndb.5097]

The input SWR is not the best. For that you have to mount R6 (I use 22 Ohm). The input SWR is then at least somewhat acceptable. 73 de Bernd

[@na5y]

Definitely! The pa-11019.blogspot link above has a selection of resistors to use on different frequencies. I certainly want to play around with this amp a bit more in the future. Thank you for the comment!

[@Davidsmith218]

anyone know of a amp that uses irfp250n and able to achieve 400+watts I've seen a couple videos but not finding much information any help is much appreciated

[@na5y]

I haven't played around with that FET myself - but I do plan to...

[@Davidsmith218]

@@na5y I ordered some irfp250 and 260. The 260 showed up first so the 260 I'm getting good results with good forward gain I used a DC to DC buck step down converter with a digital display for Bias control for testing and works great now I have had the Bias up to 3v I'm powering the system with 14.5vdc and getting 50w out with 3watts in what's would be the maximum bias volts I should run I see some talk about milliamps but not much about volts

[@JxH]

2:40 I think that the relay is drawn backwards. When PTT is asserted, the coil is activated, and would (in this drawing) push (?) the contacts down (?), away from the coil (?). That's not the traditional way to draw a relay. Relays should be shown in their relaxed state, and the contacts should move towards the coil when activated. Also, starting at about 2:55, the description of the signal flow is pretty confused. In Rx mode, the Antenna port "J1" is connected to the QRP transceiver at J2. So the Rx signals flow from J1 to J2 (not other way as you described). In Tx mode, the Xmit signal from the QRP Transceiver at J2 flows through the amplifier, and out to the Antenna port "J1" via relay pin 8 (LPF). At 3:10 you got it correct, from J1 to J2.

[@na5y]

Thank you for the comment. As far as the relay on the diagram goes - I just took one of the defaults from kicad. On the second part thanks for the correction!

[@edmoreno9308]

I'm a new amp builder and would like to know where's the best place to put the volt meter probes when adjusting the bias voltage?

[@na5y]

The place I was using was the gate of the mosfets - which is the very left most pin looking from the top of the mosfet (with the IRF530 writing right side up) You do have to 1) Make sure the amp is powered, has PTT grounded but no RF is flowing in 2) Be super careful not to short the left most pin with the middle pin on the mosfet (gate and drain) - that will blow your mosfet very quickly - ask me how I know 3) Start with the pot in the lowest position. Unfortunarely the pot on the board doesn't have a "start" position as it rotates freely. My advice would be to find this minimum position without the FETs installed. Hope this helps and thank you for the comment!

[@chrisdado]

Beware. I bought this kit and the sleeve tubes provided for the ferrite cores are non-ferrous stainless steel, zero chance of soldering them to the end caps. Luckily I have some brass tubing suitable for both core sizes, but the kit I bought was supplied to fail. Its not a question of needing more heat, I have a metcal iron, I even tried pre-tinning the ends of the tubes with a mini butane torch. Tried different fluxes, they will not take solder.

[@user-su5sq5ib3i]

Is this class c???

[@na5y]

Class AB as its currently biased I believe.

[@MrTopsoil911]

Dude stop yapping get on with assembly!

[@TheArtofEngineering]

Thanks for this looks like a cheap option to up pwr! 73 de VK2AOE

[@na5y]

Its a fun little kit - thank you for the comment!