Hi there gentlemen---

I've never built a regen radio receiver, but after having read a good deal about them here, I think that might change soon !

I'm contemplating two receivers, the very attractive AA8V Twinplex here -- http://faculty.frostburg.edu/phys/latta ... nplex.html

And the other is the little 12AT7 regen -- http://www.mines.uidaho.edu/~glowbugs/12at7_regen.html

Both receivers look to be capable of good performance for the amount of stuff inside, and I'd like opinions on them. WarBirdRadio's 12AT7 is a beauty, and I'm seriously thinking of replicating the circuit as he did !

But how would the Twinplex compare to the 12AT7 set ? Would one have more advantages, or would it be simpler, ( and more fun, ) to just build one of each ?

I really like both radios, so I might do just that !

Any and all replies greatly appreciated !

Thanks !

Tom

Hi Tom

There isn't much difference. Both use a double triode: regen detector followed by a AF stage. Expect the same performance. Component values are very similar. The 6SN7 is a lower mu tube than the 12AT7, so the regeneration might be a bit smoother. On the other hand, the higher mu of the 12AT7 means more audio gain. But neither design has quite enough audio gain to drive modern low Z headphones through a output transformer, so you'll need a pair of 2000 ohm phones.

I would run either of these off batteries for the B+. As AA8V says, the current draw is very low, the batteries should last many months.

I would not use batteries for the heaters. I'd float them: this means using AC but not connecting either side to ground. Instead, twist the wires, keep them close to the chassis, and put a 200 ohm pot across them. The wiper goes to ground. This eliminates nearly all heater hum, and is easy and cheap to do. Tube heaters eat batteries, especially the 6SN7.

There are many twin triode regens out there. For example, go to Gary's site and click on the 1948 one tube regen. Excellent notes.

http://www.qsl.net/wd4nka/form.html

Also Lindsay's book on Building a Twinplex is very helpful.

Rob

Tom,
A couple things I like about the Green regen; 1.) No 90vdc through the head phones. 2.) Built in AC supply does not cause any hum. Makes powering the receiver convienent.

AA8V did a nice job on the write up of his 6SN7 Twinplex. He has a lot of good reference material there.

I've also built the 1948 6SN7 regen on Gary's site. It was my first tube regen.

Building one of each will give you insight into both designs as well as the pros & cons of battery powered vs AC powered regens. The more varied regens you build adds to your understanding, after a while you get an intuitive sense of what works. I'm always looking for more interesing designs, not necessarily more complex but a different way of doing the same thing. Regens are a hallmark of the KISS principle. Keep it simple but make it rigid! And if you can, make it look cool.

BTW, on our Green regen with the 150v, 50 ma transformer, the dropping resistor in the supply was changed to two 4.7k resistors in parellel with a 100k bleeder. All resistors are 1/2 watt. That gives us 90vdc.
I just put it on the bench again to refresh my memory of how it was built and it's performance.

John

Hi there guys---

Swell ! Sounds like I might have to start gathering parts here for 2 receivers ! From the looks of it, parts for both should not be too hard to find. I think that for the coil forms, I'll end up making my own, but that shouldn't be too hard. We have a plastics supply store here about 10 miles or so away, they should have zillions of different sized plastic tubing, perfect for coil forms !

I was under the impression that both of the radios would be similar in performance, and now that it is affirmed, I see no reason to choose one over the other, they both look good !

John-- thanks for the notes on the Green regen, I'll write 'em down here on the printed article ! Sounds like this will be a most enjoyable homebrew set of projects !

Many thanks for the replies !!!

All the best---

Tom

By the mid 1930s, many hams seemed to switched from triode regenerative detectors to pentode designs. My 1935 ARRL handbook has only pentode regens. Here's one 'modern' version:

http://www.mines.uidaho.edu/~glowbugs/6u8receiver.htm

It's very similar to the 12AT7 regen. Something to look forward to trying.

I have one universal chassis I build on: the tube sockets, pots, VCs, etc are already installed. The PS is a separate unit. This lets me try out a given design, live with it a few months, modify it, eventually tear it down and do another. For example, I had high hopes for a 6J6 double triode but could never quite get the regeneration smooth enough. But a 3A5 version gave me the smoothest, sweetest oscillation control I've ever had in a regen. This seems to support the argument that low mu tubes make the best detectors. However, one double triode regen I made clearly worked better with the 12AT7 (medium mu) than a 12AU7 (low mu). If you build the Green 12AT7, you can also try the 12AU7, 12AV7, 12AX7, and even the 12DW7 (one half a low mu triode, the other half a high mu) (same pin out) and draw your own conclusions.

To echo John's advice, whatever you build, build it rigid. Develop a boatanchor mentality.

Rob

Hi there Rob---

Interesting looking radio ! I'll bookmark that one too for consideration here !

Cool on the "Universal chassis", kinda like a breadboard for tubes huh ? I posted a thread here in this forum asking for ideas on how to construct one, so if you wish to add a note or two, please do !

No problem on the construction of the radios should I build 'em, that will NOT be a problem ! When I build things electrical, I'm into overkill ! So you could probably paint it blue, and say it was made by Tektronix !

Seriously though, there will be no problem as far as rigid construction methods go ! If I build one or both of these sets, it'll be built like a tank !

Many thanks for the reply !

Tom

Tom, if you go with the Green regen, drop me a line. We just did a column showing how to add an additional RF stage and audio stage to the receiver, using a second 12AT7. I can mail you my spare office copy if you wish. Owe you a few for past favors. Pete

Hey there Pete--

OK, I'll drop you an email here ! Thanks !

Tom

Pete,
I'd like to see that too.

John

PM sent John !

Tom, if your offer works for John, that would be fine by me.

Pete

OK Pete, agreed

We'll see what he says here !

Regards--

Tom

Ok, I'll wait for Tom's scan of the article.

Thanks guys.

John

Robert Wilson, from the UK, built a similar radio using a 6J6 miniature tube:



The components used in the 6J6 version are:

C1: 100pF
C2: 470pF
C3: 220pF
C4: 0.1uF
R1: 2.2M
R2: 270R
VR1: 47k
L4: 4.7mH

The results of this circuit are pretty good!

Norman
KA1GUK