The Regenodyne Using the Pullen Mixer

 

This project was inspired by WD4NKA's regenodyne and a lot of talk on the glowbugs reflector on the merits of the Pullen mixer. For a great description of the regenodyne receiver and a good solid design example, see WD4NKA's web site. My version uses the following tube lineup.

 

6AU6A    RF amp

12AT7    Mixer

6AB4    Local Oscillator

6AU6A    Detector

12AX7A/6AQ5    Audio

The power supply I used is of the type that is getting more common these days as HV transformers become more and more expensive. I use an "on the cheep" philosophy when it comes to building my radios. I collected a lot of stuff when I was younger and a few years ago I bought 4 boxes of tubes at $20 for the lot including a box of transmitting tubes. I also bought an old tube based Textronix o-scope from a friend for $5 that got me a lot of 12AT7s, 12AU7s, a bunch of 12AX7s and a ton of tube sockets. That, combined with a lot of old broadcast radios that I got from the Good Will for 50 cents each gave me a good junk box fill.  I use two Radio Shack 12.6v 1.2amp center tap transformers back to back to get an isolated 120v at 126mA power supply and an additional 12.6v 1.2 amp CT transformer for the 6.3v filament transformer. I then used a voltage doubler and rectifier on the HV to get about 250v at 60mA. All solid state, not tube like, but I would rather concentrate on the radio than the power supply. This gets me what I what I need with little fuss and only an hours worth of work. The schematics that I am presenting are not the best quality but if any one wants them, I can e-mail the PDFs to them.

 

Let's look at the audio section first. I build it separate from the main receiver so that I can use it on other projects. I get a little tired of building an audio section for each radio that I build.

 

AF Amplifier

 

This circuit is actually a modified version of a Fender Champ-Amp. It originally used a 6V6 on the final but I opted for the 6AQ5 since I only have one 6V6 and I want to use it in another project but I have a half dozen of the 6AQ5s. I also opted for the version that has a bass and treble adjust since I wanted some audio filtering, something that can come in handy when working with different modes of operation. This setup gives me about 5 watts AF and when I hook up my CD player's lineout to the AF input I get a very nice, no hum, LOUD, audio signal out.

 

Now lets look at the RF amp, Pullen mixer and the Lo.

 

RF amp and Pullen mixer

 

No surprises here. A standard setup for the RF amp and the mixer is my best guess on how to use a the Pullen. I use a 6AB4 oscillator instead of the recommended 6C4 because I had no 6C4s but I did have four 6AB4s in my junk box. The 6AB4 is almost pin to pin compatible with the 6C4 and it will work interchangeably with the schematic as shown (of course, the 6C4 is octal) but it will give you a bit less output power, works for me though. The mixer I use is the 12AT7 dual triode as this is the mixer tube of choice as recommended by the staff of 73 magazine from their October 1961 article. I use the following crystals for the bands of interest.

 

4.0000MHz    Broadcast Band

4.9152MHz    160m

6.5536MHz    80m

10.240MHz    40m

16.9344MHz  20m

32.0000MHz  10m

I always include the Broadcast band in my designs since it is easy to tune to a multitude of strong station that give their exact frequency of operation. And it is easy to build a coil for this band since all you need are two Radio Shack 100uH chokes in series with a couple of wraps of #24 mag wire around one of them for the antenna link. A 200uH choke doesn't quite get you the whole band but what the heck, it is a great way to test the radio.

 

This is the detector section  

Detector Section

Again, no surprises. I've used the 6AU6A for the detector since I have a lot of them and I have read that they make good detectors.

 

Now lets look at the cabinets. This is the audio amp cabinet.

I opted for a 1930's look. Following my philosophy of junk box building or, "building on the cheep" most of the parts are from Good Will or from the junk box. The knobs are junk box, the wood is cheep, stained pine, the "porthole" speaker face is from a Good Will picture frame (.35 cents) the bars are just dowels sawed in half, the base is a Good Will prayer plaque (.50 cents), and the speaker cloth is Wal-mart remnant cloth (10 cents). The guts are equally cheep. The speaker is a Radio Shack closeout 20w speaker ($1.95), the tubes are junk box, the chassis is a G.W. candy tin (35 cents) and the pots are junk box. I did spend money on the connectors and the speaker transformer. The connectors and the transformer both came from Radio Shack. The transformer is their 70v multi watt input, multi ohm output PA transformer, it works well. All in all I recon I got about $15 dollars into the AF section.

 

Here is the receiver itself.

Again the wood is cheep, stained pine and the knobs are junk box. The front dials are old CDs with custom CD labels on them and the dial facings are G.W. plastic picture frames (35 cents each). The RF amp is located in the octal strawberry tin box (35 cents) and if you look close you can see the aluminum box that contains the 6AB4 oscillator (0 cents, aluminum scrap) just above it. The main chassis is a modified G.W. cake pan (50 cents) and the front panel is backed by some scrap aluminum to isolate the radio from the operator. You can also see the mixer and detector tubes on the cake pan. I plan to add high luminescent LEDs behind the dials to light them, again not very tube like but easy to install and most importantly they won't melt the plastic CD dials. The tuning dial on the right is the fine tuning (15 pf) dial and is actually a 6:1 reduction dial that I got from Ocean State Electronics. At about $11 it is the most expensive single piece on the radio, but I did not want to spare expenses on this part, given the importants of selectivity.

Here is a shot of the complete system on my antique (read, my cheep little auction desk) desk.

 

Questions, Comments? send to rhaub@itctel.com