Thermatron Michigan Mitty Might QRP Transmitter Kit

Everything you need to “homebrew build” this cool Thermatron QRP CW 40M Transmitter.

This new kit from Hollow-State Designs is a thermatron version of the original transistor Michigan Mighty Mite (MMM), a simple CW QRP 80M (or 40M) crystal controlled transmitter. The original version was intended to be very simple and very inexpensive utilizing a low cost TV color-burst crystal at 3.579 MHz. This version uses a 6C4 thermatron and is designed to transmit on the CW portion of the 40M band. I call it the TMMM.

The photo shows the assembled kit mounted on plywood with the optional 12V power supply. More details and history of the MMM can be found on Bill Meara's soldersmoke blog.

All parts are super-glued to a copper clad board. There is no through-hole soldering, everything is soldered directly to the board or to a component pad that has been glued to the board. The output is about 350 - 400 mW depending on plate voltage.

Everything you need is in the kit including detailed assembly instructions (download PDF here). A link to a full length video of the design and construction of an early version of the TMMM is included in the assembly instructions (also on the Video page). The video takes you through how to design and build the circuit from scratch. The kit is an improved version of the hollow-state MMM in the video and is based on my world famous book, Hollow-State Design.

Specs

Required power: 6.3V AC or DC at 150 mA, Up to 300V (typically 250V) DC at 25 mA

Thermatron: 6C4 (tested)

Output power: about 350 - 400 mW into a 50 ohm load. It depends on the plate voltage you supply the 6C4. Max plate voltage is 300V.

Transmit Frequency: the kit is supplied with a crystal in the CW portion of 40M (7030, 7040, 7055)

Second harmonic level: about -39 dB from carrier level. Due to the very low harmonic output power (< 1uM) no LPF is supplied.

Powering

The TMMM needs 6.3 V (AC or DC) at 150 mA for the filament and anywhere from 150 to 250 Volts for the B+ (6C4 plate circuit). You can power this from any HV source or build a simple power supply. The assembly instructions give full details on powering. The photos show the unit powered by the OPTIONAL High Voltage DC-DC Boost Converter 12V to 150V-420V. It is fully assembled and is available from Amazon for about $19. (It is temporarily unavailable from due to problems from the manufacturer. Check back on status).