50MHz - 28MHz RX Converter by DL5NEG
The concept of the RX converter is quite simple and nothing really new. The local oscillator is a standart colpitts crystal oscillator producing the 22MHz LO signal.
http://www.herbert-dingfelder.de/6m_conv/50mhz_to_28mhz.htm

50MHz Converter by ON6MU
Tune to the desired bandpass frequency (50Mc) with C9 until you have the best reception. Use C12 to calibrate the output frequency to your receiver.
http://users.belgacom.net/hamradio/schemas/50mc_converter_on6mu.htm

50MHz Receive Converter by EI9GQ
This is a six metre version of the two metre converter on my web page. I used 3SK45 mosfets for Q1 and Q2.
http://homepage.eircom.net/~ei9gq/50conv.html
 

An Ultra-Simple Receiver For 6 Meters by N1TEV
Here is a simple VHF receiver you can build without any special components or test equipment. This receiver uses superregeneration for high sensitivity and low parts count. It can receive both FM and AM modulated signals.
http://www.arrl.org/tis/info/pdf/9712039.pdf

Super Regenerative Receiver by JF1OZL
This is a super regenerative receiver. By the 455kHz IFT, it oscillates 455kHz. It is G2 tuned feedback oscillator. By this oscillation drain current becomes cut off situation on 455kHz.
http://www.intio.or.jp/jf10zl/regen.htm

Tune six metres on your two metre receiver by VK3YE
This converter allows reception of six metre signals on a two metre receiver. It should therefore be useful for those with single or dual band sets that do not cover 50 MHz.
http://www.alphalink.com.au/~parkerp/projects/proj6mco.htm