Minipa70 HF Amplifier Kit Testing and Review Part 4

You can purchase this kit here amzn.to/3gTd1dM
When looking around I could not find any good video's on how to put one of these kits together so here is a video of me doing one step by step hope this helps everyone out.

[@MrSoundCreation]

Hello I have a question, I build this Amp and works great, I getting full power 70+ watts on my Daiwa, but My relais don't click when I puch ptt, and als not when I release the ptt buttun from dlthe mic. only when I add the jumper there is a click. What can it be.. Best Regards

[@TheElectronMan]

That is because the way the kit is made it's for an external keying circuit you have 2 choices you can just make a PTT pedal that on activates the circuit like the Jumper does just on/off Loop one wire either open or closed or you make a PTT circuit to use the RF in radio to activate the relay I made a video on making one of these for this amp kzbin.info/www/bejne/iqWkoYGZh8-kgdE

[@MrSoundCreation]

@@TheElectronMan thank you so much for your awnser, I was already watching your other video 😃 So to be clear for myself, is that the relay is not clicking when only using the jumper right? I was thinking maby the relay was broken 🙈 Only thing is, when I use the jumper, my receive reduced a little bit. By the way, I have my bias set on 3.3 volt I use a 13.8 volt 15 Amp power supply En 4 watt input gives me 75 watts on 80 meter 68 on 40 meter Nice rig low costs, and works great Greetings from the East part of the Netherlands

[@TheElectronMan]

@@MrSoundCreation that is correct you will only hear the relay when you put the jumper on that is powering the amp on and that is why you need the keying circuit to disable it when receiving and enable it when you transmit. They are great just make sure and have plenty of heat sink and that is good setting on the bias.

[@4444panther]

Thank you for the update. Much appreciated.

[@dennis4261]

You have the PTT jumped. My question is can you put a toggle switch in line there and would it do the same thing as the jumper. Instead of pulling it out and putting it back. I am trying to make one of these work for me but am just getting started with the Ham stuff. Your videos have been real helpful. Thanks.

[@TheElectronMan]

Yes you could sure do that, as well you could make it a momentary push button switch as well...

[@rajeshhuddar3470]

Will it be possible to make a video on the biasing step. Thanks

[@Gw0wvl]

Hard switching is normal for an HF Amplifier, Not many Ham amps have a COR , CB amps as you know have a C.O.R , It's easy though to add a COR to activate the relay , You just want a capacitor , Diode , Transistor circuit to sample the incoming RF ..... Good video though , I've got the same amp and for the money it's a good little kit , I run mine with the FT-817 , It's ideal to leave under the seat so you're ready to go whenever you plug the FT-817 in 👍

[@brentbaxter1376]

Would explain how you set the bias?

[@BoB4jjjjs]

Waiting for the next video :-))

[@ransonbandy8204]

How did you adjust the bias voltage to the mosfet?

[@martincvitkovich724]

I have bias at1.8 volt. The old Heathkit am cb output is 1 watt, the output from amp is about 8 watts. Reports say the modulation is slightly on the fuzzy side, but tolerable. Any suggestions on clearing up the modulation? I have no high tech testing equipment. Weill a higher bias voltage help?

[@TheElectronMan]

You could adjust the bias up some as that will help your output but be careful to much will cook the finals. Make sure you are getting a good 13volts if using a power supply output does seem a little low but lot of things could be in play bad SWR or the radio driving it needs more output and modulation, hard to say without knowing the whole setup good thing is you know it is working now just to peak it to best performance.

[@jeromekaidor7254]

One problem with these units - it'll be obvious if you look at the output on an oscilloscope - is that they used center tap feed on the output transformer. But wait! It's not really a transformer! The two cores form two separate magnetic domains - that is, two separate transformers. The symptom is that if you look with a scope, the tip of each wave will be inverted. The fix is to feed each transistor power through a separate choke, and to not use the center tap at all.

[@rafaelceledon8389]

The spectrum analyzer test looks fishy. I see something like 0 to 30 MHz span (up side down). How did you check the second harmonic at 54 MHz and more importantly around 81 MHz the third harmonic. Mine works perfectly, but the third harmonic is only 10 dB down. You definitely need a Low Pass Filter. I agree, it is more like a 40 to 50 Watt deal.

[@TheElectronMan]

Good point I can't really make it out good but I agree it looks like I have span wrong woops but I have checked it multiple times guess I just grabed the wrong setting that time but rest assure mine tested pretty clean across all the bands but I agree I would use some pass filters if you are going to use it in the ham bands.. BTW If you have a nice bench spectrum analyzer you want to give me I would love to have it that little China handheld I have is not real user friendly to say the least LOL.

[@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?

[@TheElectronMan]

I would check and see if you have voltage at the transformer first but it could be a number of things hard to say without me seeing it. With zero watts out sounds like connection issue on the board somewhere.

[@Johnyrocket70]

Something is on backawards

[@akeem11h]

Have you tried the 100w version?

[@TheElectronMan]

No but I am thinking about building one :)