EMRFD Message Archive 11309

Message Date From Subject
11309 2015-07-06 12:34:10 Ashhar Farhan A simple 25 watt linear
I have been using a 25 watt linear for a few years now. This is based on the sec 2.11 in EMRFD. I have used the two-part article written by Rick for QST as the guiding principle to design this linear. 

- f

11310 2015-07-07 07:26:53 don_k5uos Re: A simple 25 watt linear

Nice, thorough write up.



11311 2015-07-07 07:52:45 Ashhar Farhan Re: A simple 25 watt linear

really the entire 'blame' should go to rick. his paper (quoted at the end of my write up) is an excellent, nuts and bolts approach to designing the linear amplifiers. i just followed his procedure.

- f

11312 2015-07-09 14:59:20 iq_rx Re: A simple 25 watt linear
Nice work Farhan,

My series of amplifier articles was based on the way we actually build early prototype amplifiers using some new device that isn't necessarily characterized for the frequency or class of service we need.  It seemed to me that the community had lost the ability (and enthusiasm) to explore using whatever was available to try something new and different.  The techniques we use to press a junk box transistor into service are similar to our approach when device engineers give us something bleeding-edge from a brand new process.  One of my current grad students uses nearly the same method with 50-year-old NOS vacuum tubes and brand new GaN devices from an unreleased process.  If he gave me a choice, I'm not sure whether I'd rather have his 3.5 GHz GaN linear amplifier or 18w EL84 guitar amplifier...last I checked, he wasn't interested in giving up either.

There's some theory involved, but it really is experimental methods in RF design, where all of your experience and intelligence are engaged a set of experiments with a particularly interesting, and often unfamiliar device.  The approach works best when devices are inexpensive (or we have enough of them) that we can stress them, burn out a few, and explore higher voltages and alternative heat sinks.

Thanks again--nice work, and nice writeup.

Best Regards,

Rick KK7B
11313 2015-07-09 19:20:33 kb1gmx Re: A simple 25 watt linear

Really nice.  I do like that you provided the attenuation for 
power matching and stability.

11314 2015-07-09 19:35:46 kb1gmx Re: A simple 25 watt linear
Hi Rick,

GaN fets... I've blown them up too. ;p   It was a prototype. 

My favorite piece of work is using MRF247 a controlled Q high band (136-175mhz) 
VHF power amp.  According to everyone they don't work at 6M.  So I built a 75W 
amp around one for 6M SSB and its both stable and tuned up real smooth.  Its 
been in use in the mobile for about 8 years to open antennas, shorted antennas, 
no cable at all (oops!) without fail.  It survived characterization and testing as the 
data sheet was useless.  The best part was it was a pull from a fried Mirage 
2M amp, its companion was toast so they get replaced as matched pairs.

Its good to see people experimenting and then doing something with the