Testing the Minipa70 HF Amplifier Kit

[@zman4150]

I built one a year or so ago. Little by little I added to it (BPF) and installed it into a box, mounted the LED's from the BPF to the front, and added an Arduino wattmeter found in a recent QST. I see around 55W out with the high setting from my 817d, and have worked JA from the East Coast on 20 using FT8. I added a fan to my heatsink because it will get quite warm & don't want to blow anything up! 73

[@mikep-j894]

I also bought one of these, more for self education than expecting a miracle and indeed it does generate RF (but the supplied FETs were pretty shocking) It may help others to know you can improve the spectrum at the bottom of the band quite considerably with a Z-link shorting winding of heavy wire through the output cores. As built this is really 2 independent transformers, as each primary only drives one core, and linking in anti-series them so one drain voltage is forced up as the other goes down really helps the waveform. It is very informative to put the drain waveforms on a scope- the distortion is actually visible, so 2F and 3F must be about 10dB down on carrier before modification. I agree that a decent 'how to get the best out of this' instruction is sorely needed.

[@drvigg9083]

I was looking for the primary center tap for this big transformer in the photos, and was surprised I didn't see one. Are they driving the finals in parallel, which does nothing for harmonic suppression??? Push-pull would at least mitigate the even harmonics. It also looks as if they have a single bias for both '530s. Okay if you have a matched pair, but at this price point, I wouldn't count on it! If I wanted to use one of these for constant-envelope modes (eg., CW, RTTY/(A)FSK), how low could I set the bias? A push-pull pair, each operating in Class C mode, should work FB with a constant-envelope signal and some harmonic filtering. I suspect that would reduce the heating a bit. Or would I be better off going the switch-mode route, say, Class E?

[@mikep-j894]

@@drvigg9083 Be careful, it is really nothing like one transformer with centre tap - if anything more like two transformers, one primary tube per FET connected from drain to B+, with the multi-turn secondaries in series. A moment to sketch this out shows this is not really the right thing to do at all,, no wonder it is rough - what you really want is to force one FET drain to be pushed up in voltage to about twice V+ by the other is pulling down near 0V. Hence the shorted 'Z' winding improving the waveform quality, though a true centre tapped bias choke would be better. If you have a dual channel scope, all is revealed. Mine has now had so many hacks it looks nothing like the original. Un-modified you will not get anything like the stated power continuous, it is very much an optimistic peak pulse power rating, Mike

[@martincvitkovich724]

I built a Heathkit GW12 CB Base in the 1960's when I was a teenager. I found a working GW12 at the Dayton Hamvention. I replaced all tubes and tuned it according to the manual. I can only get .5 to .75 watts out of it. Will that be enough power to run this little amp? I would think with .5 watt in it should put out 3-5 watts. You mentioned the resistors getting hot, would it help to mount resistors of a higher wattage? I am expecting the kit to arrive July 17 2022.

[@thuff3207]

Thank you for the video and showing the build. I look forward to seeing the spectrum on the different bands.

[@Yankees_1996]

Did you put spectrum on this to see if it is a splatterbox? This would be great for uBitx QRP rig.

[@HamRadioConcepts]

My only question. How does it look without the LPF? There is no filters at all on this board so I am guessing it is spurious all over the place??

[@RobBob555]

not good, it works but i get bad audio reports..

[@kriegertherottweilerpuppy7899]

More reviews sir I'm interested in this linear amplifier.😊 Thank you for all the good information you gave to us about using this Chinese made linear amplifier. 😉👍

[@helpporatsastaja]

I hae built this and its still to test. These videos and webpages about someone making it before were very helpful. I had resorted to looking at the pictures of coils how many rounds they needed to wind. Manuals are also quite rare for this, I don't know whether there exists any in Chinese. Still need to acquire load resistor to test this before getting it online. Did cost really nothing, 25 euros including postage.

[@W1RMD]

Thanks for doing a video on this. I've been looking at these on Ebay and I appreciate your thorough, honest review on this thing. 73's-Ryan

[@narpat007]

what about harmonics and how strong are those, you did not talk atall about that !

[@SarahC2]

I see you added a jumper to PTT...... is that because the relay detects the TX RF on the input? Why have a PTT input at all in that case? Just wondering if you know!

[@johnwest7993]

I heard no mention of what voltage you were running the amp at or the current setting you used on the bias.

[@JamesCutlervk2tim]

You need to do a 2 tone test on SSB to check linearity.

[@neodiy]

would u share the schematic where i can download it?

[@robertjonasson2527]

What's it look like on a spectrum analyzer for spectral purity?

[@MattHeere]

What gauge is the wire used for the transformers in your amp? I just got my kit, and instead of the orange wire I got some 30AWG stuff that looks like it should be in an old wire wrap kit.

[@WT2D-Michel]

Great video, whats the typical current at 70 watts???

[@sudberceni257]

Good evening, I have an XDT-PA100 amplifier. I have a cable for yaesu ft 818. I have a red and black wire on the amplifier. with what color do I connect to the cable cat

[@menashewalsh5128]

Resistor R6 is marked up on the board but does not appear to be on your board or the circuit diagram.

[@scharkalvin]

What part number are the MosFets? I know that IRF510's will NOT give 30-50 watts at 13.8 volts!

[@CarNRadio1]

How long would it hold on ft8?

[@R2AUK]

Thanks for sharing.... To be honest, somehow I doubt that IRF530s are any good on 28 MHz. Or are they?

[@johnwest7993]

I haven't got my amp put together yet, but I expect about 15 Watts on 10 meters. Of course, that depends on how much drive power you run, how hot you bias the MOSFET's, and what voltage you power them with. These FET's can be run on 30 to 40 volts. If you run the amp on 13.8 V don't expect even half of what he claimed as output power, and he made no mention of those most important parameters.

[@TheAcehere1]

How did you connect PPT link to the transceiver

[@rudykay5618]

Does it work on 11 meters ssb?

[@gnosticcommunications8933]

Mine exhibits a lot of harmonic output in the absence of an output LPF, which is needed before putting 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.

[@webmastercaribou7570]

Can the entire circuit board contact the heat sync?

[@williamogilvie6909]

There might be an EB note in Motorola's RF Application Reports book.

[@linkmaticelectronicspakist4693]

One question sir i have a 3 watt power FM transmitter which is transmitting audio well if i give output of that transmitter to this rf amplifier input will it work? i think it will work well for further longer ranges. do you think it will transmit my audio to further distance like commercial FM radio stations?

[@rajeshhuddar3470]

Connected the minipa ro my Ubitx. Get a very high SWR. What could the reason.

[@rajeshhuddar3470]

I get a very high SWR when connected to my Ubitx. Where am I going wrong. Inputs from you will of great help. Thank You and 73. VU3RHU.

[@DM5UE]

by now there is a kit on ebay assembled or DIY with up to 200 watts (24 volts /16 amps, 5 watts input). I bought the assembled one and I must admit it is very good soldered an wired

[@tallman0416]

Can you try to use MRF9180? I expect more big power.

[@RobBob555]

hhmmm.. built this but you have to have the PTT jumper in position for it to work, sadly when the PTT circuit is working.. it greatly attenuates the receive signal..so AFAIK you NEED to make a PTT cable from your radio for this to work correctly ? it does not seem to have RF sensing..

[@rodneyhodge652]

What transistors/MOSFETS?

[@EdwardStorlien]

My amplifier does not amplify the signal... zero watts out. Have tried with new pair of MOSFETs. Biased correctly, but only 20 mA current on idle. What could be the problem?

[@lovelycollection100]

Discotec tour Solder when Solder the MOSFET

[@JimCoupeTQ]

Should that PTT jumper be in place default? I cant get this thing to fire up.. hmmm that relay should click right ?

[@JimCoupeTQ]

My Relay circuit did nott work.. And the ground to the relay was OC. Im not sure if you have to isolate the heatsink. Also my bias circuit was cooked

[@MrSoundCreation]

A little late after 2 years, but I have this problem to. The amplifier produce his power around 70 watts, but the relais not clicking bij puch the Mike. What can it be. Best Regards

[@DonDegidio]

I bought a HYS TC-300 300W amplifier from a Chinese seller on Ebay, but it did not come with any low pass filters. You need to be careful about 3rd order IMD products with this style amplifier. I later found that this amplifier would have a clean signal if it's output was only 70 - 90W. I wanted to use it with my 5W Flex 1500. I just picked up a 200W dummy load to test what input I need to drive it to 90W output. I noticed in the link, several images of the output are shown. It's a shame they didn't have the stop frequency set for about 150Mhz. You would be able to see the 3rd order IMD of the amplifier. WB3BJU

[@Geewhiz811]

Yep, you are correct. I haven't tested it yet on the spectrum analyzer but I am guessing I will see harmonics on it at full output. You can minimize this if you can adjust the bias separately to each transistor to make it as linear as possible but that is not very practical. I plan on making some plug in low pass filters for the common bands I would like to use. QRP Labs makes some nice plug in low pass filters but they are only good to about 15 watts so those wont work. I am also going to decrease the bias voltage so the amp will only peak at 50 watts as opposed to 70-80 which, from what I have read on the datasheets for the transistors (IRF530N) Is really pushing it.

[@DonDegidio]

What I did was buy a complete LPF diplexer from a Russian seller. I'm going to use a rotary switch to select the filter for each band. Here's a link. www.ebay.com/itm/LPF-diplexer-1-8-30MHz-300W-SSB-CW-HF-amplifier-low-pass-filter-MOSFET-LDMOS-RM-/172203976141?hash=item28182825cd:g:VjAAAOSwl-FXNFyd WB3BJU

[@dennisf7086]

I've been tempted to try one of these, but with many other projects on the burner I think I'll pass for now. Antennas come first before more power. Thanks for the video. 73, Dennis, K9DPF.

[@adamslarren2100]

Did you ever get a chance to put this on a spectrum analyser? I just ordered one of these and a low pass filter to use with my bitx40. Thanks for posting this video.

[@Geewhiz811]

Not yet but I have been meaning to do so. I have been doing alot of work on the simulcast system so some things have been pushed to the side for now.

[@adamslarren2100]

I built one the other day and it seems to work just fine. Do you think this unit could be run on 24v for a cleaner signal? And do you know what else would need to be done such as lowering bias voltage?

[@Tishers]

@@adamslarren2100 The IRF530N transistors are not rated for that level of supply voltage.

[@TheFlyre]

hi sir this is 39 mhz? im looking for that

[@JamesCutlervk2tim]

Need to see the 2 tone IMD test

[@Deano-Channel]

The Transistors they supply with this kit are FAKE IRF530, I have built 10 of these kits and have fitted genuine IRF530 Transistors from Radio Spares, by the way great Video.

[@mshadow64]

Is the relay RF sensed? or does it need a ptt wire? I am considering getting one for my little QRP I just got done! Let me know please!

[@JamesCutlervk2tim]

PTT wire active low.

[@RobBob555]

where do i take the bias voltage readings from ? is there a Test Point ?

[@RobBob555]

?i is it the gate ? earthed where drain ?

[@techtrendzy]

Hi KC2IRV,,,nice demo !! Hav you tested it in SSB without using an additional LPF...how's the result; does the relay circuitry bypass it during recv mode...de vu3cgb

[@Victurf]

Hello, Do you have a connection diagram for this amp? If so, would you be so kind as to send it to me? Thank you. Thank you. Jean-Pierre

[@joewilson2258]

To keep the power transistors cool pi some thermal paste between them and the heatsink .

[@DylanMcNamee]

Out of curiosity, what bias voltage would I use if I wanted the peak output to be 50W instead of 70W (with 5V input)?

[@MrBugsier5]

Thats not to adjust whit the bias!! YOU HAVE TO DO THAT AT THE INPUTside.

[@liamfrost8814]

would you be able to put 10 watts into it

[@lovelycollection100]

In no out yes

[@TeddyD802]

A build video would be very helpful

[@tallman0416]

Please try to IRF1404 FET transistor.

[@puma9354]

I build one and im using it with a ubitx, my swr is kinda high, my tuner cant tune it down

[@rajeshhuddar3470]

Same is the case with me. Is your problem resolved.

[@AA1PR]

nice amp, soldering doesnt look to bad on this unit voice peaks might be higher for $20 how could you go wrong

[@Geewhiz811]

Yeah, I forgot to show the SSB test on video, its peaks around 80 watts with 5 watts of drive. The soldering was done with my 45 watt station, I under estimated how much heat the bottom ground plane of the board would suck away so some of the joints aren't the nicest to look at but they are all solid and none of them are cold.

[@marylouiseacebedo706]

Hm heat on top and heatsink on bottom, how's that working out for you?

[@plop55]

Leonard Belcher just fine, how about you?

[@nickk48]

The board has an opening where the MOSFETs mount. The MOSFET's tabs are bolted directly to the heatsink (with a thin insulator between). This is standard practice. de WA5BDU

[@RobBob555]

lenny.. you are a cock.

[@HamRadioConcepts]

hahaha on your comment

[@davejones6313]

Do you know if 500mw would drive this amp ??

[@RobBob555]

nah.

[@JamesCutlervk2tim]

It would, but not to full output.

[@JamesCutlervk2tim]

I've built mine, it works, but when adjusting the bias, be sure to terminate the output into a load, or it will oscillate!

[@RobBob555]

WHERE do i take the voltage reading from for bias adjustment is it the transistor ? if so which legs ?.. BCE ? thanks

[@RobBob555]

??????

[@JamesCutlervk2tim]

@@RobBob555 Measure at the wiper of the pot. These transistors are enhancement mode MOSFETS, not BJTs, so no C-B-E, it's G-D-S. 2.7Vdc at the middle leg of the pot is what you want.

[@nappingpup105]

So I picked one of these up. Now, what's the procedure for powering it up, without damaging either the amp or the transmitter? It come with a PTT connector. How does the PTT connector function? What if I simply want to send CW, for example?

[@TehMG]

IRF530N is a very poor choice for an HF linear amplifier. Sure, it's dirt cheap compared to proper RF transistors, but it's first of all designed for switching applications, not linear operation. As such, linearity of the amplifier is likely to be quite poor, as well as reliability issues due to thermal limitations while operating such a MOSFET in the linear region at high power levels. Yes, specialized RF transistors are much more expensive (easily 50% or more of the total parts cost of an amplifier), but they are specifically engineered for linearity, thermal dissipation, and controlled impedance throughout the operating frequency range. See how in DK9JC's test results the input SWR and gain of the amplifier is all over the place? That's because the impedance characteristics of the IRF530N are very frequency dependent, and parasitic capacitance and inductance in the transistor's construction play a major role when operating these transistors in RF linear mode.

[@Mark300win]

MGKZbin Account what transistor do u suggest as a replacement?

[@701rdcondo8]

Dont use the supplied FAKE mosfets. They will FAIL because their gain is excessive at low input levels (100mw). Get the REAL ones if you HAVE to use these MOSFETS. Without real instructions and REAL parts, you are wasting your money and the kit is really an exercise in soldering SMDs.

[@johnwest7993]

Hams often go with what's cheap and will work, as these amps do. They are famous for ingenious adaptation. If the transistors pop it's about $3 to replace them. Anyone with a few thousand bucks in their wallet is welcome to buy a beautifully engineered amplifier made with all the best parts. As for me, I can build a good output filter real cheap.

[@TehMG]

@@johnwest7993 You can filter out harmonics but you can't filter out IMD (intermodulation distortion) because those distortion products are so close to the desired signal.

[@johnwest7993]

@@TehMG, I don't plan on using them as linear amps anyway. I'll be using them on CW for portable ops. I wanted the option of another 30 to 50 watts on the output of my QRP rig when I'm up in the mountains with the backpackable 40 meter vertical I put together. I like running low power, but I'm not a complete QRP fanatic.

[@JosipBedenicec9A2QP]

Great working with my mcHF SDR transceiver

[@mshadow64]

what are the drivers? irf530?

[@RobBob555]

lol who knows .. mine had ALL info filed off !

[@Tocsin-Bang]

This linear is not linear if built directly as per the parts. What is missing is R6, it should be 18 ohms 5 watts.

[@geekthesteve6215]

I tried to look at the schematic and I could not find R6. I see it on the PCB and it looks like it balances the input on the gates on the MOSFETs or am I misinterpreting? Will not having this resistor take these parts out of the linear range? Would you explain why you have this concern a little more? Thanks in advance. Thinking of building an amp for an old Tentec QRP rig I have. I probably will build something using an LDMOS and not this one, just trying to understand better.

[@richardknack968]

Does this have an RF sensing PTT circuit, or does it have to plug into an accessory jack on the radio? -de KC8MWG

[@RobBob555]

no RF sensing.. you really need a PTT jack from rig..as RX signal is attenuated when relay is switched.

[@nickk48]

Nice video. I'm building one now and some of the info here and in some blog posts by others is quite useful. - WA5BDU

[@trevorjacobs8593]

Hey Nick! I just ordered one of these today to build up to go with the K2. Can't beat the price. I'm hoping to dump the T/R relay and use PIN diodes for T/R switching. Was talking to Jay W5JAY about it today. How did your build go? Hope life is treating you well. BTW I'm in Texas now. 73 Trev K6ESE

[@bloguetronica]

Those kits now cost around $40 on eBay. Nonetheless, it is a very well though kit and will work very well.

[@akepatinagaraju8564]

Amplifier BREMI BRL 40 - 70 about plz sir

[@TeddyD802]

How did you solder the SMD's?

[@RobBob555]

mine were already soldered on.. even tho the listing shows them not on.

[@billryland6199]

You will need a LPF to reduce the harmonics to a legal level.

[@SCTV59]

Building one for usdx 5w HF transceiver. How do you get around the PTT circuit? Jumper? Do you recommend adding low pass filter. Work mostly 20m DX. Thanks. Kk3sc

[@SCTV59]

SSB BTW.

[@AtomicElectronCo]

Here's a link to a schematic...not perfect but pretty obvious. PDF link: 115.28.16.44:81/file/4874.pdf

[@MAV3NX]

What FETs are they using?

[@Mr_Meowingtons]

IRF530n look at the video.... :/

[@joebasque2655]

Nice video, good shots of the amp.. Got mine in today.... Thanks to you and other info. Looks like I have what I need.. 73 Joe VE1BWV

[@waseemsltj6096]

Please half transistor nombre send me

[@obamatheimposter]

Question, can this amp be used with a radio that has an internal tuner? (I have a Xiegu G 90) or must an external tuner be added?

[@corkystephan5073]

The answer, is no, the tuner needs to be after the transmitter, so it can tune the antenna to the transmitter.

[@raafatalheety826]

73 from baghdad de Yi1hxh

[@RobBob555]

I was in Baghdad when you were in your dads bag !

[@Mr_Meowingtons]

if they made a 100w ver i would bite...

[@RobBob555]

they do.. but defeats the purpose of a QRP rig.

[@ericzerkle5214]

There is a 180 watt version.

[@Mr_Meowingtons]

​@@RobBob555 so does this kit.... if i want to run QRP ill not plug in the amp... Durrrrrr

[@graplingurty]

No Band pass, dirty amps cause RFI on multiple harmonics with out filtering.........

[@minnesotanature]

I have been testing it out on 20 meters at about 50 watts on scheduled contacts , no harmonics so far. I don't have equipment to test just amp.

[@RobBob555]

@@minnesotanature no it DOES have a dirty signal.. im getting bad audio reports with it.

[@TelstarElectronics]

A kit with no instructions... and you're recommending? LOL

[@mrkattm]

Being that you are a License General class operator I know that you did not transmit with that amp without the low pass filters in place. You should know better.

[@plop55]

It was a test, the amp was not used regularly that way. You need to find better ways to spend your time other than useless comments on KZbin.

[@RobBob555]

Michael.. Go Fuck yourself !

[@ericzerkle5214]

"You should know better." Yeah you sound like a typical snobby old fart ham. How about giving the guy good advice instead of brow beating?

[@ericzerkle5214]

Surface mount scares me away because I have bad eyesight.

[@rajeshhuddar3470]

How do you check the bias voltage. Which is the C7 capacitor. Cannot locate it.

[@sudberceni257]

Good evening, I have an XDT-PA100 amplifier. I have a cable for yaesu ft 818. I have a red and black wire on the amplifier. with what color do I connect to the cable cat