The PINNACLE of Home Brew Amps - Or Not...


2007-04-13 12:15 am
From the looks of this project everything in it was salvaged from junk equipment. It is the paramount diy on a budget design.
Other than a missing rectifier what makes you think it never worked? If this unit was constructed by a young teenager I would say they did quite a good job for a first time project. At least they gave it a go and did not quit.
If you look at some of NP's very early work you would never believe the same person brought us the fabulous SS amps we see today.
It is a nice conversation piece. I like it. Tad
it is a ham radio amplifier. Those are ham hf radio bands, 10 meters (28-30MHz), 15 meters (~21MHz), 20 meters (14MHZ), down to 160 meters wavelength (1.8MHz I think), that's a huge antenna!!! The FCC is currently trying to "steal" the airwaves from the hams to make room for more telecom companies $$$. What a shame. Isn't it a man's natural right to use the airwaves? I mean in a couple of decades we'll be paying to breathe air. Anyway, this amp reminds me of a friends story about a homebrew kilowatt cb radio amplifier, it would give the guy the runs every time he turned it on. loll
Its all good!

Hi all
As a ham radio opperator myself, i have seen many examples of home brew gear that gets close to this.
Yes, it is definately an RF amplifier for the HF bands.

Looking at the photos, the coils / tuning caps on the RHS form what is known as the tank circuit which is basically a Pi or Pi/L filter.

The long and thin upright inductor which looks like a solenoid is the main HV choke, which are actually quite difficult to design, due to the hideous RF currents present.

One of the bigest problems with designing the HV chokes, is to ensure that it is not resonant near any particular opperating frequency.

I have witnessed first hand a HV choke that worked great until the amp was switched to the 14Mhz band, and it caught fire.

I enjoyed the fireworks, the owner / builder did not.

Presumably the RF it generated was so great that it triggered headaches and bowel movements every time the ptt was operated. Probably cb folklore ;) I have noticed though, that prolonged cellphone(milliwatts) conversations cause discomfort, althought it could simply be the phone getting hot. The fcc has strict rules for ham radio antenna placement/power dissipation because many of the bands/wavelengths are close to the dimensions of the human body and its structures. Resonance?
My previous post was nothing more than a passing comment, as this after all, a diy audio forum.
At he the risk of going really of topic I feel that the following comments are warranted

BlackUnikorn said:
The FCC is currently trying to "steal" the airwaves from the hams to make room for more telecom companies $$$. What a shame. Isn't it a man's natural right to use the airwaves?

The telecom companies, ( I suspect that you mean phone carriers) have no interest in the HF spectrum.
World wide acceptance of the importance of these bands, and the public / free service that hams provide guarentee their existance for many years to come.
Agreed however, that the same cannot be said for the spectrum above 1.5 Ghz

BlackUnikorn said:

The HV choke or plate choke in high powered RF amplifiers must carry a tremendous level of RF Currents. The inductance of these devices must be such that it will not resonate anywhere near the required HF band.

Anyone that has tried to make one will instantly relate to the difficulties in trying to "park" a resonance away from a subject band, ensure a low resistance to currents and still ensure that it is a resonable size, will know what I am talking about.

My apologies to all for going off topic