100 Watt 13.8 Volt Amplifier for LF by GØMRF
This Class D switching amplifer was designed to enable anyone with an interest in LF to get onto the band quickly and without the need to invest in a separate higher voltage power supply.
http://www.g0mrf.com/classd.htm

136 kHz preselector and amplifier by IK2PII
This project was developed to reduce the image frequency response of my direct conversion receiver. It can also e useful as front end for HAM communications receivers and also for selective level meters used as LF receiver. The project focus was selectivity, not gain.
http://www.qsl.net/ik2pii/lf/prea136.htm

137/472 kHz Power Amplifier by W1TAG
...for BPSK, chirped HELL, and other modes generated by sound cards, linear transmitters are significantly cleaner, and may be necessary to fit the signal in the regulatory bandwidth, as well as offer some relief to other users of the band. Realizing that I was interested in operating with such modes, I considered building a linear power amplifier.
http://www.w1tag.com/XESTX.htm

400 W Power Amplifier by GW4ALG
The 400 W power amplifier (PA) uses many of the components from an old KW1000 HF linear amplifier (including the original pair of 572B valves). The amplifier was purchased for under £200 and has been modified from a switch-tuned grounded-grid configuration to an aperiodic (untuned), push-pull amplifier, rather like the QRO Class B Modulators of the 1960s.
http://www.alg.myzen.co.uk/radio/136/400w_pa.htm

A 400 Watt Low Frequency SSB Linear Amplifier by W5JGV
After obtaining a pair of surplus Motorola Starpoint channel modems to use as SSB exciters at WC2XSR/13 on 168 KC, I wanted to build an amplifier to boost the power to about 400 watts, which is the maximum licensed transmitter output power for WC2XSR/13.
http://w5jgv.com/400w-ssb-amp/index.htm

Broadband 5 Watt Amplifier for LF and MF by GØMRF
If you are getting started on MF or LF and plan on using the low level output from an SDR radio, or a homebuilt transverter, then you will probably need an amplifier with high gain and enough power output to drive a larger power amp.
http://www.g0mrf.com/5W%20linear.htm

LF 5 Watt Amplifier by WD2XES
This small linear amplifier has been useful for low-power testing. It would also make a good driver for a higher-powered amplifier that required real driving power. The present model is built in a cast aluminum case, and is used with an external power supply. My bench supply provides 30 VDC, good enough for a clean 8 watts.
http://www.w1tag.com/5watt.htm

Medium Power 137kHz Linear Power Amplifier by G4JNT
This project was conceived on the back of an envelope after running a WSPR beacon thorough my 600 Watt switch mode Power Amplifier, and setting light to the plastic shed containing the loading coil.
http://www.g4jnt.com/Linear_LF_PA.pdf
 

Medium Power Linear Power Amplifier For LF/MF by G4JNT
This is an updated version of the LF Linear amplifier described in [1] After giving that amplifier to G0API to use on PSK31, I decided I did actually need one (to work him with) so this updated version was built.
http://www.g4jnt.com/Linear_LF_PA3.pdf
 

Quarter Kilowatt Amplifier for L.F. by GØMRF
The amplifier described, uses four low cost Power Fets to generate 250W output on the European 136 kHz L.F. allocation. The circuit uses traditional RF construction techniques, and has 50 Ohm in- and output impedances.
http://www.g0mrf.com/lf.htm