Archive for January, 2012

“Look Ma” 12K5 Kit is back

January 29, 2012

In the Spring of 2006,  almost 6 years ago, we designed an operating 12K5 oscillator that was crytal controlled and had output on 40 meters. It was submitted and written up in the May 2006 issue of CQ Magazine. It was inspired by ealier articles that introduced new hams to the old breadboard transmitters that used electricity directly from the household mains without any isolation transformer. Open wires and bare connections were used all over the board.  Our little transmitter used a “space charge” vacuum tube which was designed for automobile radios in the early 1960’s, before transistors were production ready. This 12K5 tube used 12 volts on the filaments and on the plate circuit.  Works great except the power output is very low.  Remember, volts times amps equals watts, and, with such low voltage you just arent going to get a lot of power out.  Power, whether at audio or radio frequencies,  is under one watt.  We also sell our vacuum tube audio amplifier with a 12K5 output tube, and , yes, the volume is just fine for a quiet room or headphones, but not much more.

We quit selling the little 12k5 transmitter kit when crystals became scarce. You see, we like to include the 40 meter QRP crystal in each kit. Well, for now, we are able to do it again.  Please check eBay or www.pastimeprojects.com for purchase of these kits.  The kit includes a wound coil assembly with link coupling, a small trimmer capacitor pre soldered on the terminal strip, a nice solid oak block finished by our Amish neighbors, and tested 12K5 vacuum tube, a great manual for step by step easy assembly, and clips, capacitors, sockets, resistors, wire and hardware to make this a fun project. You wont send CW very far on 40 meters,  but distant DX communications was not the intent of this fun, learning kit.  Please consider purchasing this little piece of history. Makes a great conversation piece for your shack.  By the way, power can be supplied from your 12 vold dc power supply rated at one amp or more.

73 Glenn      www.pastimeprojects.comRemember When QRP 40 M transmitter

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whats happening FT 243 crystals 6V6 6L6 tubes Dummy load kit.

January 9, 2012

We just discovered out little 5 watt dummy load kit disappeared from the web page.  www.pastimeprojects.com . We reinserted it on the parts components page and,  after checking inventory and starting another build cycle, we advertised the one in stock on eBay. It was sold before the ink was dry… So please take another look at this little kit as new ones go into our stock inventory.

It is a great way to catch up on a little bit of assembly and some easy soldering.  Large solder joints and heavy wires. Great project for the individual or a club.  Dummy load can handle up to 8 watts for short periods of time.  When the little box gets warm, just let it cool off a little. Great for qrp or cb rigs running 5 watts or so.  Monitor your signal, check power out, all without using an antenna and interfering with other stations.

Have you noticed the vacuum tubes and crystals we sell have a unique feature you wont find anywhere else?  We check them in actual transmitters for frequency and activity.   These will work in your ‘boat anchor’ or ‘homebrew’ tube type transmitter.  Each tube or crystal usually carries a certification tag.  If you want to be sure, just ask when you order.  They will work to your satisfaction.  Our FT-243 crystals are, for the most part, the original sealed units from the WW II period. They will handle more current than the typical small crystals sold today for qrp use.  If you are using crystals for 160, 80, 40, 20, 10, 6 or 2 meters, please email us at pastimeprojects@yahoo.com for the frequency range you are interested in.  We know some am rigs survive for 6 and 2 meter use, and we may be able to help.  We also have some high end 75 meter crystals that might be good for amplitude modulation. We simply dont have time right now to inventory all of the crystals so we will look for your specific needs as you ask. 

When you compare price,  remember is the other guy offering testing AND shipping and handling costs in his selling price?  Best regards Glenn NN8G