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

How many watts will the LDMOSs transistor do on 27MHz. U peeked my interest and knowledge. I grew up working on Tube type TVs. Dad worked on them in 50s through 80 but now im interested in power transistor’s

Have you done any work on amplifier designs for lower frequencies, like for the 160 van, or they do 500 kilohertz ham band mosfet seemed that they would be a great fit for those. Being low frequency they should give you a full potential

Thank you guys for embracing modern RF design and the use of spectrum analyzers and oscilloscopes for modulation. There's quite a bit of knowledge out there and it would be a shame if it was not putting good use. That CB radio kept getting the bad rap of crappy linear amplifiers that spewed harmonica over the band, and splattered constantly.

Show off.... 😉 I throughly enjoyed your video... Awesome job!

Great video ! Do you work on amps for others ? i have a TS DX 250 that needs checked out ? If you do please get back to me? Thanks

To me the first obvious challenge is the heatsinks being upsidedown.

A book on how this exact design with schematic will work and explanations of circuit is planned?

я посчитал по формулам.для 3 квт и 50 вольт питания. выходной трансформатор должен иметь 6 витков. а не 4 витка.

Your shack looks the same as mine, we follow the same paths. But your have a great gift in explaining matters. Thank you!

What's with the 2 adaptors on the VNA? are they to change the gender or as I was thinking just pass throughs to reduce wear and tear on the VNA jacks.

To read swr

Could you have just used the radio to key up the amp and the radio set to read sir and tuned it that way?

Using the antenna tuner to measure what's going on, define the measurements results with the VNA and THEN use the conjugate of the measurements. You do understand smith charts I would say. Well done!

One of the best video's I've seen on this topic in quite a while. Also a joy to listen to the tone of your voice while explaining though stuff, very relaxing, down to earth and convincing at the same time. Thanks much, I've learned a lot this time! 👍

would not be easier to drill holes through the aluminum and use longer screws :)

Hi. Thanks for the great video. Would be very (and completely) useful if you could post in the comments the specific Motorola ANs that you are refering to. Thanks in advance.

thanks for the info. what is the max input power it can handle ? 73' Ingmar PD1IM

Very nice stuff. I am a Ham and this is really impressive! You are not an appliance operator!

Hey man. MUch respect for what your doing. I have a question. I’ve had the tin based solder grow whiskers over time somehow and short stuff out. Where as silver lead based solder always has done what I’ve ask of it. Have u ever seen this. I’ve never seen it on a component joint. More on where wires are soldered. Was jus curious if you have ever seen it or heard about it

I have a 100 amp DC to DC power supply runs up to 54 v if I could get one of these amps what box would I need. And how many transistors would be in it. And what would be the wattage? Guesstimation?

I saw the lead on the input bias choke bouncing up and down as you were tapping on the choke and I wanted to yell that to you - 3 years after the fact. :)

The key to designing any analog amplifier is maintaining the allowable loss of the power device. Start by measuring the efficiency of the designed amplifier and check the allowable loss of the selected device. For LDMOS devices utilized, it is generally indicated as 1300W~1800W. You can't use all of this~ It is also important to note that the heat dissipation area of ​​these LDMOS devices is too small to allow for such losses. For 65% efficiency, the limit is 600W of continuous output. In the case of SSB mode, the average value is only about 40%, so in theory it is possible to produce about 2.5 times more output, but in reality, it is unreasonable to exceed 1.5 times as efficiency is lower. Please don't waste expensive devices! And the important thing is negative feedback. Less negative feedback causes oscillation and impairs linearity. If negative feedback is reduced due to the desire for large output, the linearity of the output decreases and becomes unstable. It is recommended to use a negative feedback resistor that covers large power. This serves to expand the BAND WIDTH of the output because it provides not only negative feedback but also a resistive load. Good luck~ From SOUTH KOREA~