18 dB LT1253 DDS Amplifier by K8IQY
This 18 dB gain amplifier was built Manhattan-style to evaluate the Linear Technology LT1253 dual video amplifier as a candidate output amplifier for DDS systems employing the Analog Devices AD9850 and similar devices.
http://www.k8iqy.com/miscellaneous/18dblt1253ddsamplifier/lt1253ddsamp.htm

500 Watt PA by SMØVPO
Although I am an avid proponent of QRP (using reasonable power levels), there are times when I wish that I could run 1,000,000 watts and point it in a particular direction.
http://sm0vpo.altervista.org/tx/500w-txt.htm

KISS 70W Power Amplifier using VHF Bipolar Transistors by PAØFRI
This 10 - 80 m amplifier is using two VHF bilolar power transistors PHILIPS BLW60. The gain of a VHF bipolar transistor can be very high but the amplifier was perfectly stable in the experimental phase.
https://pa0fri.home.xs4all.nl/Lineairs/BLW60PA/pa-blw60eng.htm

A low cost 600 watt ultra-linear amplifier by IW5EDI
This compact little amplifier is the brain-child of Pat Murdoch, ZL1AXB, in Auckland, New Zealand. It is only 11″ wide, 4″ high, and 9″ deep. In most respects it is a typical grounded grid linear amplifier, with the exception of a rather unique tuned cathode input circuit that was developed by Pat over 10 years ago.
http://www.iw5edi.com/technical-articles/a-low-cost-600-watt-ultra-linear-amplifier

A MosFet PA by G3ONL
This circuit was described in Sprat 73 by G3ONL and is capable of 5 watts out on all bands. Diode D1 is included to protect the power device, preferrably a hot carrier or gold bonded germanium diode.
http://www.zerobeat.net/g3ycc/mospa.htm

Allmode 5-band RF Power Amplifier for the HF 80, 40, 30, 20 and 17 meterband by ON6MU
This project uses a widely available IRF510 MOSFET. This N-Channel enhancement mode silicon gate power field effect transistor is an advanced power MOSFET designed, tested, and guaranteed to withstand a specified level of energy in the breakdown avalanche mode of operation.
http://users.belgacom.net/hamradio/schemas/hf_5-band_mosfet_amplifier.htm

Basic Linear Amplifier by SMØVPO
This is both a project AND a bit of basic theory regarding the design of wide-band HF power amplifiers. As usual, it is prompted as a result of e-mail in which I have to repeat myself over and over again.
http://sm0vpo.altervista.org/tx/rf_pa_cct_00.htm

HF Bands QRP Linear Amplifier by SMØVPO
This is a rather unusual QRP Power Amplifier design, with a wide frequency response; within three dB's from 300KHz to 30MHz. Overall gain is in the region of 16dB and the final output power may be well over four watts.
http://sm0vpo.altervista.org/tx/linear.htm

HF Linear RF Power Amplifier by YBØAH
It is nowadays hard to find replacement for RF Final tubes such as 6146B 6JS6 etc. Stocks in the market seem to be very limited, besides it is very expensive too.
http://yb0ah.tripod.com/homebrew/project/pwr_amp/index.html

Linear-Endstufe mit PL509 / PL519 durch DL2YEO
Die PL509/519 sind zwar keine echten Senderöhren, aber diverse Artikel und Bauprojekte im Internet belegen, dass man damit durchaus eine zufriendstellend funktionierende KW-Endstufe (Linear RF Amplifier) für wenig Geld bauen kann.
http://www.qrp4u.de/docs/de/PL519/index.htm

Mini power Williamson Amplifier by JF1OZL
When I was about 14 years old, I learned about Williamson amplifier and Ultra Linear amplifier on the radio magazine. Such amplifiers was made by many tubes and Push Pull type transformers.
https://www.emilio.com.mx/jf10zl/williamson.htm

My 813 Linear Amplifier Project by WB8ERJ
Actually this rig came back to haunt me. You see when I was in high school, I was a member of an Explorer post that was into Ham Radio. There was a big room full of WWII surplus gear. This particular rig was our "pet" project.
http://www.wb8erj.com/813amplifier.htm

PL519 FRINEAR 150, 150 W HF Amplifier by PAØFRI
Being a passive-grid amplifier, most of the input power is dissipated in a non inductieve (carbon) resistor applied to the control-grid of the valve. This type of linear has many desirable features, ...
https://pa0fri.home.xs4all.nl/Lineairs/Frinear150/fri150eng.htm

PL519 400W Grounded Grid Amplifier, FRINEAR 400 by PAØFRI
The regular visiting of ham flea markets is a money-saving way to obtain parts for a home-brew linear amplifier meeting the requirements of the Telecom authorities.
https://pa0fri.home.xs4all.nl/Lineairs/Frinear400/Frinear400eng.htm

Push-pull Linear Amplifier with NE592 Driver by DL2YEO
Transformer T1 matches the relatively low impedance present at the VFO FET gate to the balanced inputs of the NE592. With a unipolar power supply, it is necessary to bias both inputs to roughly one-half of Vcc.
http://www.qrp4u.de/docs/en/rf_ampl/index.htm

QRO GU-84B Tetrode by NI4L
The GU-84B is a ceramic-metal forced-air cooled tetrode intended for use in power amplifiers with distributed amplification and for SSB-signal amplification with output power up to 2.5 kW at frequencies up to 75 MHz ...
http://www.angelfire.com/nb/ni4l/gu84b.html

QRP HF Linear Amplifier by SMØVPO
This project was a particular surprise for me in that the BC547 (equiv 2N2222) can be used to build a 500mW linear amplifer covering the entire HF band with excelent spectral purity and no neutralising at all.
http://sm0vpo.altervista.org/tx/qrp-hf1.htm

SMØVPO 500mW Linear Amplifier by VK2ZAY
This is my implementation of SM0VPO's tiny HF linear amplifier. You can find his original page about the design here: Harry's Homebrew Homepages.
http://www.vk2zay.net/article/04

TB3/750 FRINEAR-750 by PAØFRI
I purchased an old Yaesu FL-1000 (4 × 6KD6) (fig») that had changed bands and countries several times, in the course of which it had undergone various modifications.
https://pa0fri.home.xs4all.nl/Lineairs/Frinear750/FRI750uk.htm

The 500W PA by G3YXM
This is the base station version of my Throbatron MosFet PA, it hasn't gone off bang for over ten years now! This is a two-band (160 and 80) version. I have tried it on 40, and publish filter details, but the output is only about 250W and it needs more drive.
http://www.wireless.org.uk/throb.htm

WA2EBY IRF510 amplifier by LBØMG
The WA2EBY amplifier is a famous linear amplifier project published in QST in March and April 1999 by Mike Kossor WA2EBY. As this amplifier can give up to 50W out with 1W drive, it is a perfect pair for my Softrock RXTX amplifier.
http://diycrap.blogspot.com/2016/06/wa2eby-irf510-amplifier.html