The AA8V Twinplex Regenerative Receiver
by Greg Latta, AA8V

Twinplex Receivers Built By Others

Twinplex Receiver

Twinplex Receiver Pages:
 Main Page and Exterior Photos  How To Use A Regenerative Receiver
 Interior Photos of the Receiver  Receiver Schematic Diagram and Circuit Description
 L1 and L2 Coil Specifications  6SN7 Dual Triode
 Twinplex Receivers Built By Others  Modifications


Introduction:
For me, the greatest reward in putting together a web site such as this is for someone else to build the twinplex. It is always fascinating to see how folks overcome obstacles and come up with their own versions of twinplex. Since it is always helpful to see variations and what others have done, I have decided to add this web page showing receivers built by others. I hope you will find it useful in building your own twinplex.

73 and have fun,
Greg Latta AA8V

 George Sifakis's Twinplex
 K5DP - Mark Miller's Twinplex
 NI8N - Jack Hubbard's Twinplex
 Stephen Bargiacchi's Twinplex
 ON4KMC - Michel Declercq's Twinplex
 N2EGA - Michael Harris' Twinplex



Twinplex Receivers Built By Others:

George Sifakis's Twinplex

 
George Sifakis's Twinplex Receiver - Front Panel:
This twinplex was built by George Sifakis from Athens, Greece. George built a prototype first to work out all the bugs and make sure it worked, then he built this beautiful final version. George used only junkbox parts in his version of the Twinplex.

Front panel controls are as follows:
Top Left - Main Tuning
Top Right - Bandspread
Bottom Left - Antenna Coupling
Bottom Right - Regeneration

Even though the volume control seems missing, it isn't. George uses an external audio amplifier with the Twinplex, which has its own volume control. George found he wasn't using the volume control on the Twinplex very much, so he simply replaced it with a 147kohm resistor and connected the grid of the audio triode (pin 4) to the ungrounded end of the resistor. This effectively keeps the Twinplex volume all the way up all the time.

 
Sifakis Twinplex Front View
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Photo by George Sifakis


 
George Sifakis's Twinplex Receiver - Rear View:
In this rear view of George's receiver the placement of the components can be clearly seen. Note that George has mounted the tuning capacitors on a thick aluminum plate, which provides for great tuning stability. Other components are mounted on a vertical phenolic strip that can be seen between the tube and coil and the tuning capacitors. An audio output transformer can barely be seen behind the phenolic strip at left, under the tuning capacitors.

George's bandset tuning capacitor (upper right) has two sections. The smaller section is used on the shortwave bands, and the larger section is used on the AM broadcast band. Switching is cleverly done by a link inside the coil plug.

 
Sifakis Twinplex Rear View
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Photo by George Sifakis


 
George Sifakis's Twinplex Receiver - Side View:
This side view of the receiver nicely shows off George's 3-D wiring, which was done just for fun. Even though it may not be the best thing for RF circuits, it looks great. To do it, George measured the distances with a small ruler, made all the bends, and when it was completely done he soldered the two ends in place.

The octal plug at left in the photo is for connections to an external box which is a combination power supply / audio amplifier / speaker / coils container.

 
Sifakis Twinplex Rear View 2
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Photo George Sifakis



K5DP Twinplex

 
K5DP Twinplex Receiver - Front View:
Mark Miller, K5DP, built a beautiful oak wooden cabinet for his Twinplex receiver. However, he also used an aluminum ground plane which eliminates any hand capacitance effects.

Mark was lucky enough to have a National HRO-50 PW vernier dial and capacitor assembly that he could use with his receiver. This assembly is a truly deluxe tuning assembly, and it is nice to see it used in a Twinplex.

Controls, from left to right, are as follows: AF Gain, Regeneration, Main Tuning, Fine (Bandspread) Tuning, Antenna Coupling.

 
K5DP Receiver - Front View
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Photo by K5DP


 
K5DP Twinplex Receiver - Front And Interior View:
In this picture both the front panel and interior of the receiver can be seen. The HRO drive assembly utilizes a right angle drive assembly so the tuning capacitor is parallel, rather than perpendicular, to the front panel.

 
K5DP Front and Interior View
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Photo by K5DP


 
K5DP Twinplex Receiver - Interior View:
In this interior shot, the complete HRO drive assembly can be seen. Though it has four capacitor sections, only one of these is used with the Twinplex. Mark has also labeled the front panel control functions on the top of the front panel, which makes for a nice uncluttered front panel.

The tube and coil can be seen at the upper left in the photo, and a barrier strip for power connections can be seen at upper right.

 
K5DP Interior View
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Photo by K5DP



NI8N Twinplex

 
NI8N Twinplex Receiver - Front Panel:
This twinplex was built by Jack Hubbard, NI8N, who uses it on 160m and 80m. The large knob on the left is the bandset control and the vernier knob on the right is the bandspread control. At bottom, from left to right, are the antenna trimmer, volume, and regeneration controls.

 
NI8N Twinplex Receiver
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Photo by NI8N


 
NI8N Twinplex - Rear View:
In this view of Jack's receiver, the bandspread capacitor is at left. Notice how small the capacitor is, only about 10pf. This, combined with the mechanical vernier dial on the front panel, gives a very slow tuning rate so the receiver may be used on the 160m and 80m ham bands.

Jack has used insulated flexible couplings on the shafts for the tuning capacitors, which makes for smoother tuning than without the couplings

My hat is off to Jack for actually using the twinplex to make QSOs, as that is a real challenge. I met him on the air when he was using his twinplex and asked him to send these photos. Many thanks, Jack!

 
NI8N Twinplex - Rear View
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Photo by NI8N



Stephen Bargiacchi's Twinplex

 
Stephen Bargiacchi Twinplex Receiver - Front Panel:
This twinplex was built by Stephen Bargiacchi from Italy. Note the beautiful numerical scales on all of the controls which allow him to easily reset the controls. Having a numerical scale on the antenna coupling control is particularly handy, as the setting of the antenna coupling is critical, and affects the overall tuning of the receiver.

 
Bargiacchi Receiver Front View
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Photo by Stephen Bargiacchi


 
Stephen Bargiacchi Twinplex Receiver - Rear View:
This is a rear view of Stephen's Twinplex. It was taken while Stephen was building the receiver, so some of the wiring is still missing. The variable capacitor at left is the bandspread control, and the small variable capacitor at right is the antenna coupling control. Note that the antenna coupling control is mounted on a white plastic "L" bracket and a plastic shaft is used. This is necessary since the antenna coupling control must be floated above ground.

It looks like the AM coil is plugged in at the moment, and he has done a nice job of winding that coil. The bandset capacitor is the variable capacitor in the middle of the photo with the large black vernier dial attached to it.

Stephen has mounted banana jacks on the back panel to make connections for the filament voltage and the B+ supply. This is one of many ways these connections can be made. (On my Twinplex I used a barrier strip.)

 
Bargiacchi Receiver Rear View
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Photo by Stephen Bargiacchi



ON4KMC Twinplex

 
ON4KMC Twinplex Receiver - Front Panel:
This twinplex was built by ON4KMC, Michel Declercq. All of the control functions are clearly marked on the front panel. The large knob at lower left controls the bandset capacitor which is coupled to the yellow scale on the upper left.

 
ON4KMC Twinplex
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Photo by ON4KMC


 
ON4KMC Twinplex Receiver - Rear View:
This is a rear view of ON4KMC's twinplex. The large capacitor at right is the bandset capacitor, and the small capacitor in the middle is the antenna trimmer capacitor. The bandspread capacitor is underneath the chassis, where it can't be seen. The plug in coil is visible at the left.

A careful look at the bandset capacitor will show that Michel has removed plates from the rear section of the capacitor to lower the maximum capacitance. He has also used the dial cord drum on the bandset capacitor to make his own vernier drive for the bandspread. A string runs around the drum to a shaft and knob that are below the chassis, and not visible in the photos.

 
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Photo by ON4KMC


 
ON4KMC Twinplex Receiver - Coil Set:
This is a picture of the coil set for ON4KMC's twinplex. The lowest frequency coil is on the left and the highest frequency coil is on the right.

There are many ways to make the coils for the twinplex, as you can see here and elsewhere.

 
ON4KMC Coil Set
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Photo by ON4KMC



Michael Harris' Twinplex

 
N2EGA Twinplex Receiver - Front View:
This is a photo of Michael Harris' Twinplex receiver. Michael built his receiver with a wooden front panel, which is fine, since this is how these receivers were often originally built, particularly in the 1930s, when metal would have been scarce or expensive.

Michael is very lucky to have a National vernier dial to use on his twinplex. These work great but are hard to come by nowadays. I used a larger National vernier dial in my 6x2 superheterodyne receiver.

 
Harris Twinplex
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Photo by Michael Harris


 
N2EGA Twinplex Receiver - Rear View:
Michael is the first person to use my conventionally wound coil for the AM band, which can be seen at the upper right in the photo. This type of coil avoids the necessity of finding an AM ferrite antenna, and uses standard magnet wire and winding techniques.

Though it looks like the chassis is all wood, Michael used a sheet of aluminum (not visible) as a subchassis under the wooden chassis top. This gives the receiver a vintage look while still providing for a good ground.

Michael uses a pair of binding posts/banana jacks for his headphones, and these are visible on the top of the chassis at the bottom right of the photo. Since Michael's receiver was built primarily to receive the AM broadcast band, he did not use (or need) a bandspread capacitor.

 
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Photo by Michael Harris



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