Відео

nice heatsinks

I love the comedy your dog provides.

Oh dear the choke had become un soldered. no wonder it had issues.

Great video. Just one question. I have looked at a few pairs of Zetagi B300P they have 6x power level positions. What i found is that each power position has a slightly different reflected power back to the radio, each position passes via a different group of resistors mounted near the power level switch. However when in position 6 which bypasses all resistors i see the highest reflected signal to the radio. SWR at the radio jumps up 2 or 3 times worst. What I'm thinking is that they tuned the amplifier with fixed capacitors for an average taking into account the effect of the attenuation resistors. But the problem is that at full power the reflected power is the worst. I'm thinking the best is to add variable power to the radio, keep the linear always at full power and try to tune the transformers for less reflected power at full output power. I think I will tune with variable caps then remove them and measure the value then add fixed caps of that value in place. Keeping the variable caps for the next amp tuning.

Thank you!!!

Sharky where do I order your pallet kits from ? specially 27MHZ

You are happy with ur construction and results...

youre still doing better than me, i have a very similar board with a blf188xr and its outputting HALF of the input and i have no idea why

How can u rely upon s parameters in such nonlinear circuit? Even large signal s parameters wont fit and wont give accurate Z meassurements

I like your style. Like.

Cool channel. Nice mullet!

I will build an amp. I will need to use it on 28.000 - 29.700 MHz SSB. Should be in good shape?

It is Awesome that you got it fixed. Happy to see it working great. And the owner will be happy too!

Good afternoon Sharky!! Eh, are you still selling the pallet kits and will you ship to chi.....errr...canada?

very nice

you misunderstand how the splitter works. If the input is 50 ohms the 2 outputs will be 100 ohms each. If used as a combiner with 2 50 ohm inputs the output is 25 ohms. The way you modify the relays is how I was doing it with 16 pill boxes in the 1980s. Now I use vacuum relays. Pricey but flawless.

So well explained, this beginner was able to follow it all. Thank-you.

Probably a dumb question but could a liquid cooled copper block be used on something like this? Totally new to this stuff so I apologize if it's a stupid question.

This is eaxctly the video I needed to watch today! I've been getting into building audio amplifyers and compressors with amp circuits within them etc. recently and have been trying to learn more and more about how they do what they do on a deeper level. I've been tracing the signal through the circuit with my scope and playing about trying to understand certain things ... and being a tube circuit (although not much differant to a transistor circuit in what I was trying to figure out) I couldn't work out why the HV power was being supplied to what appeared to be the tube signal output .... but this makes that make perfect sense, and was kind of what I assumed it must be, but had no way to know for sure without this vid! It's just taking an elevated AC voltage from the change due to what the tube lets through from the grid signal on the annode plate side, rather than taking it from the cathode and the output being only what the tube lets through like I initially thought (untill I looked at the circuit and was like well it's attached directly to ground through a resistor, so it can't be that). Thanks for uploading this!

Hi at what frequency did you tune the amplifier?

Very well done, and I am sure it will be helpful to many in this RF hobby. Cheers

Здравствуйте поделитесь пожалуйста схемой уселитель благодарю

Love your videos mate ... you're giving me so much to think about, and you've introduced me to a number of rabbit holes that I feel obligated to explore! 73 ... VK4KYT

Most all solid state mobile amps, back in the early days of the MRF-454 and 455, had tunable transformers. Someone, along the way, decided to measure the tuned padder cap, and replace it with an equivalent value using a silver mica cap or caps. Now, they're using surface mount silver micas. However, knowing that copycats are out there, who don't really design anything, they merely copy what others have done, and do not know how this came about, nor how these values are determined. It's why they produce splatter boxes. I'm not for sure if Arco is still in business, as that is who supplied us with padder caps years ago. DigiKey doesn't list them anymore.

U got the boot

this is the stuff that keeps me up at night., i just don't have your brain power to understand or figure things out lol.. thanks,

where did you hook your powersupply to on the circuitboard

You need to do a two-tone test on any RF power amp, particularly an external linear amplifier. If you don't do the test you won't know the linearity and the in-band intermod products. You will quickly find that you need to back off the drive to get reasonable linearity. For SSB operation your 3rd order products should be at least 26dB below your carrier. These 3rd order intermod products are what causes "splatter" on adjacent channels. All ssb tranceiver's output power is limited by the 3rd order products and they run them below their peak output capability. That's why it's always possible to overdrive the PA and get more output power.

Can I buy 3 units?

Follow up? Follow up? 🙏

Really appreciate your explaination. Would you mind sharing the device model of your high Q tunable capacitor (which seems quite compact there)? I am thinking of tuning the circuit myself for high power amplifier, would really appreciate your help. - Yuanchen

It is quite easy to understand. An open wire takes a current to be loaded capacitively. But the current does currently not know that the wire is open at the end. But the current in an inductive is not allowed to jump we know from physics. So what should the current do if it reaches the open end? It increases the voltage so that the current is still running. It increases that much that the sparc is visible. The higher voltage at the end then acts like a generator and returns direction sender. If it reaches the end, it sees the transistor source-drain resistor to be loaded with the energy of that reflected wave. Is this complicated?

I'm afraid I'll disappoint you. Base key, all measurements with nano VNA you should do with an unsoldered transistor. Otherwise you will need to connect VNA to the 50 Ohm terminals and match the S11 and S22 transformation lines with the fully powered transistor and approach the (50+j0) impedance, of course theoretically.

I am way behind you with my learning curve but the way that you have explained what and why that you took this approach was understandable and surprisingly simple for my 60 year old brain to obsorb... I truely enjoy and appreciate the content that you so selflessly create for us... 73 my brother! Ps... I'll have some of whatever your dog is chowing on... Sounded delicious! Larry KF4LBG

What’s the point of bulky transformer for matching when LC matching components could be also be used. In my opinion it’s much easier to design a matching network using these components?

Whats a tool?

@4:14 The goal of gate resistors has nothing to do with SWR. They work as parasitic suppressors. On high bandwidth devices operated at lower frequencies (most power LDMOS have quite high gain even above the GHz), these gate resistors along with gate capacitance create a LPF, decrease the input Q and lower the response/gain of the LDMOS above operational frequencies preventing destructive oscillations . Again, these LDMOS devices by themselves have a huge open loop gain even at GHz frequencies where negative feedback could easily become positive and the amp could potentially become a power oscillator if no preventive measures are taken when used at such low frequencies. Gate resistors are a cheap but effective safeguard on such low frequency applications. A similar technique can be seen in power tube amps, where parasitic suppressors are placed in series with the plates.

How You Doing Sharky, Hope Things Are Well For You & Yours. From KC8FPT In Cincinnasty Ohio

Excellent troubleshooting this tricky problem & Correction componet deduction with tools on hand !!! ....I also thought a Conjugate Capacitor 'bout 200 pF (--28 ohms) would be the required Reactance correction.....Your 170 nH inductor is also +28 ohms....Thx for posting video..

3 biggest things i have seen killing these devices. Too much bias voltage. Overdriveing them and now enough cooling.

You’re not worried about the BeO contamination from blown up fets?

Back to the bench?

If in doubt use a door knob cap. Short length TC 12 coax makes an indescribable cap too. Iv used these on 50 88-108 and 144 mhz. No experience with 10/11m.

I really enjoyed the video, with so many catastrophic situations that can happen to this amplifier, well seen! the auto oscillation thing. Regarding the problem of placing a thermocouple, or thermoswitch, it is a very good idea, I have been manufacturing amplifiers for years, and we must take into account one thing that all builders ignore, when we use copper heat sinks, together with a copper heatsink. aluminum, we create a temperature cloud at a certain coefficient in the middle of the joint of the two materials, with which the copper part thermally collapses and stops being efficient. I manufacture my amplifiers entirely with copper heatsinks, it is more expensive, but much more efficient. Greetings from Seville Spain, EA7KNR, J.Manuel

Thank you for explaining how it works, it was very helpful for me. I assembled the same circuit, but when setting it up, I got a capacitance of 1600 pF on the primary side and 270 pF on the secondary side with an impedance of 5.5+0j. I think this is too much capacitance; on your diagram, the values are almost 5 times smaller. What could be the reason for this?

very insiteful troubleshooting, as I'm learning how to build my own HF amp.. this level of explanation on fixing issues is helping me avoid issues.

That fan is your cheat code! 😂 Nice setup! Thank you for sharing your results... 73

Are you back to selling these in kit form as you have in the past by chance?

Very, very good lesson! I will drink a half glass of vine. No vine, russian vodka.

I learned a lot even at my age. Always loved electronics but never had chance to go to school for it