-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Linear repair
- Thread starter 357magnum
- Start date
I do agree with the others that say it's best to purchase another amp. Whether a used one or new one that would be up to you, but if you insist or need someone in the future Scorpio amplifiers seems to know what he's doing. I have not sent him anything nor do I know of anyone who has personally gotten work from him, but his YouTube videos tell a story of somebody who takes their time and does the job correctly. Good luck. 73
Just ignore that 54 megahertz Spike. How many times did he say spectrally clean? LOL. I've never seen this one. it's a gas! Thanks for sharing it. 73
54 MHz is the second harmonic of 27 MHz. EVERY solid-state amplifier produces second-harmonic energy.
A peek inside any "legal" solid-state ham amplifier reveals low-pass filters. They are switched in line between the amplifier transistors and the antenna socket to match the band you're using. This suppresses the harmonics before they can reach the antenna.
Second-harmonic energy is just a side effect of any solid-state amplifier circuit. "CB" amplifiers leave out the harmonic filter. Costs money, and doesn't make it sell any better. If you make it big enough so that it won't burn up from excessive drive power, that costs even more money. This is what happened to the harmonic filters that Maco and Varmint tried to include in their tube-type boxes decades ago. They were big enough for the "normal" harmonic energy from a proper drive-power level. And as soon as the question "How hard can we drive it?" gets asked, that harmonic filter burns up and gets removed.
Spending the additional money to include it raises the sale price, but nobody will pay your higher price when they compare it to the guy who leaves it out. They'll buy his cheaper "dirty" amplifier every time.
The incentive in the CB-amplifier market is to beat the other guy's price for the same or more wattage.
And the incentives are stacked AGAINST selling a clean amplifier. Or one that's clean enough to sell as a legal ham amplifier, anyway.
Sure you could build it. But they won't buy it.
73
A peek inside any "legal" solid-state ham amplifier reveals low-pass filters. They are switched in line between the amplifier transistors and the antenna socket to match the band you're using. This suppresses the harmonics before they can reach the antenna.
Second-harmonic energy is just a side effect of any solid-state amplifier circuit. "CB" amplifiers leave out the harmonic filter. Costs money, and doesn't make it sell any better. If you make it big enough so that it won't burn up from excessive drive power, that costs even more money. This is what happened to the harmonic filters that Maco and Varmint tried to include in their tube-type boxes decades ago. They were big enough for the "normal" harmonic energy from a proper drive-power level. And as soon as the question "How hard can we drive it?" gets asked, that harmonic filter burns up and gets removed.
Spending the additional money to include it raises the sale price, but nobody will pay your higher price when they compare it to the guy who leaves it out. They'll buy his cheaper "dirty" amplifier every time.
The incentive in the CB-amplifier market is to beat the other guy's price for the same or more wattage.
And the incentives are stacked AGAINST selling a clean amplifier. Or one that's clean enough to sell as a legal ham amplifier, anyway.
Sure you could build it. But they won't buy it.
73
And then they'll complain about the 54 MHz spike in the one they did buy, we are our own worst enemy in this hobby.
Ouch ! Thank you for that vid ! I just purchased a cheap Sirio 27-4 I'll just run my old Gray on low power ( if needed ) always prized myself on trying to run clean , 11m or not !lol
Maybe I'm missing something, he pointed out the 54mhz spike. So forgive my ignorance on this but is that 54mhz spike normal from a dirty amp or is it from a dirty signal from the radio?
What's funny is he says the only thing he can do to knock the second harmonic down considerably is put a 54mhz band-pass filter in it,
That would knock the 27mhz output down considerably & not reduce the second harmonic at all,
biasing a class C amp does not make it spectrally clean
Anybody can buy some test gear and talk shit on youtube to drum up trade like the snakeradio guy.
That would knock the 27mhz output down considerably & not reduce the second harmonic at all,
biasing a class C amp does not make it spectrally clean
Anybody can buy some test gear and talk shit on youtube to drum up trade like the snakeradio guy.
not a hit at you bob ..you ok in my book
the rant ..
lol he has no clue about bandpass filters and their function .notch yes.. bandpass no
personally i am more concerned about IMD
imd is the thing that splatters the band not harmonic transmissions ..you can have legal harmonic levels from any transmitter (with in ITU spec) but you can still destroy half the band with IMD which is a parameter most cb techs never mention ..
it is possible to have a cb radio or any transmitter for that matter to be 60db down in harmonic content (2nd/3rd/5th/7th/9th harmonic whatever ) and meet FCC spec or RSM spec or whoevers spec you dam like and still be a nasty "transmutator" of IMD causing adjacent channel interference to your mate 50miles away
for the ones lacking knowledge on IMD i present a link
https://en.wikipedia.org/wiki/Intermodulation
for classes of transmission and a bit about imd and linearity i present this link
http://www.qsl.net/va3iul/RF Power Amplifiers/RF_Power_Amplifiers.pdf
ok off the rant back to working the world with 2 watts a bit of wire and a mode thats narrower than the minds of some of the "techs" that use youtube as a sales pitch
If you knew who that guy was that made the video and if you knew what his technical abilities were and you knew that he was desperately trying to copy Mark Sherman with all his phrases and that the test equipment he has is simply for a theatrical presentation and he has no concept of how to use that equipment you would totally see the humor. He's really good friends with Trucks CB sales and Forrest Gump if you know who those guys are. He had a janitorial position at the radio shop in Ennis Texas about 30 years ago and somewhere along the way decided to start calling himself a technician.
His job is to remove that Spike before he sends that equipment back to his customer. He admits he is clueless how to do so.