The Murania “One Transistor” Boy’s Radio Kit

INTRODUCTION & CONSTRUCTION

The Four State QRP Group (Oklahoma – Kansas – Arkansas – Missouri, in case you were wondering), founded in 2003, is one of the best developers and retailers of high quality and reasonably priced QRP (low power) ham radio and other do it yourself electronics kits.

I have a few of their kits over the past few years, most recently including the Bayou Jumper Paraset transceiver last year. I presently have the NM0S 4S-Tuner/Antenna Coupler kit on order.

Tonight I tackled one of their popular new non-ham radio kits, the Murania, a one transistor Tuned Radio Frequency (TRF) AM broadcast band receiver kit. The kit was designed by NM0S, David Cripe, who has engineered several of the 4SQRP kits.

The documentation for the Murania tells of the advent of transistor radios in the 1950s and how radios with 1 or 2 transistors were considered toys and therefore not taxed like radios containing more transistors. These 2 or less transistor “toy” radios became known as “Boy’s Radios” and are highly collectible today.

The designers of Boy’s Radios employed some creative design techniques to maximize the performance of these minimalist circuits, with sometimes amazing results. The Murania kit was inspired the design of those simple high performing transistor radios.

Unpacking the Murania kit.

My Murania kit arrived quickly within 2 days of placing my order online….WOW!

The Murania features a unique construction technique called “Pittsburgh Construction” developed by W0MQY , Joe Porter, in which components are soldered to the surface of pads on a silk screened double sided PCB.

Like other 4SQRP kits, the assembly manual needs to be downloaded from their website. Documentation is very good with clearly expressed step by step directions, but lacks pictures which might be helpful in illustrating potentially confusing steps for the newbie builder, such as the correct orientation of a polarized component such as an LED, diode or electrolytic cap.

The 4SQRP website suggest the kit can be built in about 2 hours time, and that was my experience. The radio is built in five stages… (1) wind the coil, (2) build the voltage regulator, (3) build the audio amp, (4) build the RF circuit, (5) final assembly.

1. Winding the Coil

The first task is to wind the coil which consists of 37 turns of No. 22 AWG enamel wire around a ferrite core. The instructions call for covering the core with a layer of masking tape first and using masking tape to hold the first and last winding in place.

My first attempt at
winding the coil.

I chose to use black electrical tape, and that was definitely a mistake – the electrical tape made it difficult to compress each winding snug against the previous winding and it didn’t do a very good job of holding the first and last winding in place.

I believe this may have also affected performance of my radio (see below). I am planning on modding the set and rewinding the coil with 61 turns (also, see below) and will use the recommended masking tape at that time.

2. Voltage Regulator

The first circuit constructed is the power supply/voltage regulator which consists of installing the volume control pot and attached power switch, one electrolytic capacitor, the battery connector, another capacitor and a resistor and the LED which serves three functions – power on lamp, signal strength indicator, and voltage regulator delivering 1.6 – 1.8 +VDC to power the radio.

I appreciated that the instructions called for testing the voltage regulator circuit before proceeding on to the audio amp stage. My Murania was putting out 1.792 VDC+ within the acceptable range of 1.6 – 1.8 volts.

3. Audio Amplifier

The Murania has a single stage of audio amplification based on the 2N3904 NPN transistor that drives the speaker through a matching transformer.

Other components in the stage included a pair of capacitors, a single resistor and of course, the transformer and speaker.

4. RF Stage

The bulk of the RF work is handled by a single IC, the TA7642, which has its origins in the late 1960s. Equivalent to the ZN914 and MK484, the TA7642 contains ten transistors and performs the task of RF amplification, audio detection, and automatic gain control. The documentation points out that with the TA7642, it is possible to construct a Tuned Radio Frequency receiver with useful sensitivity and selectivity, using only a handful of components and that this device served as the basis of many radio receivers that were the successors to the Boy’s Radios.

The 10 transistor equivalent circuit of the TA7642 per the datasheet.


Like the voltage regulator and audio amplification stages the RF stage went together without a hitch. All parts in the kit were properly identified and clearly referenced in the assembly manual. The etching on the circuit board made mis-installation pretty much an impossibility if you’re paying attention to what you’re doing.

The assembled Murania TRF radio ready for testing.

5. Final Assembly

After testing the radio to make sure it works (it did), the last step was to assemble the rest of the cabinet which is comprised of five additional pieces of yellow PCB material with pads strategically placed to match up for soldering to connect.

The pieces fit together perfectly, although I should have taken time as recommended in the directions to file off burs and rough spots so the pieces fit together more perfectly. Overall this is a pretty ingenious way to build a radio cabinet.

PERFORMANCE AND MODS

I was very pleased that the radio worked right away. I was able to pick up several AM stations with ease. Stations received were clear and the audio, while not as loud as I would have liked, was not distorted.

One problem I did encounter that is worth mentioning is that after I tested the radio on my bench I attached the back to the radio and brought it to my wife to show off my handiwork.

She was impressed, however when she turned the radio on, the LED lit up but there was no sound coming from the speaker – absolute silence – UGH!

I took the back off and quickly diagnosed the problem – the top of the 9V battery was shorting the speaker terminals – a problem easily fixed with a piece of electrical tape across the speaker terminals.

I did expect the radio to be a little more sensitive than it was initially and I realized that the radio’s performance might have been inhibited by my sloppy coil winding.

The unmodified Murania Schematic ©NM0S, 4SQRP Group

Online I found a list of three simple mods for the radio published by Jim Marco, WB2LHP in MI, the third of which that involves additional windings on the coil so I thought I’d give them a try.

Here are Jim’s mods…

1. Detector Gain Control…

FLOAT the wiper lug of R3 and place a jumper between the PADS for the R3 wiper and the high side of R3.

Lift the leg of R1 that intersects with R2 and R3 and connect a jumper between the floated leg of R1 and the wiper of R3.

According to Jim, this allows R3 to control the gain of the detector stage in the TA7642 acting similar to a regen control where there is both volume and gain reaction. The audio amp runs wide open and R3 should be adjusted for the best sounding audio.

2. Reduced audio distortion…

Changing R2 from 1K to 2.7K biases the output stage of the TA7642 for linear operation.

3.Frequency coverage and dial mapping…

Increasing L1 from 37 turns to 61 turns and removing C8 centers the frequency coverage and makes the dial tracking spot on…

The revised schematic based on WB2LHB’s mods

I am pleased to say that the mods were easy to accomplish and I had no difficulty with any of them. I did not have a 2.7K ohm resistor on hand so I tied a 2.2k and a 470 ohm resistor in series for R2. Using the recommended masking tape instead of rubbery electrical tape on the ferrite rod made a world of difference too – winding the 61 turns was a snap.

My modified Murania – notice the new ferrite coil, the replacement of R2, the removal of C8 on the right, and the jumper going from R1 over the speaker to the VR R3.

And how did it work? Even better than before – the radio seems to be more sensitive and is picking up more stations and the audio is definitely more crisp as promised. If you’re looking for a fun one-evening project that will take you back to your earlier days of melting solder – the Murania TRF receiver is worth building.

©2019 JMSurprenant

Alec Bradley Nica-Puro Rosado Gordo

I stopped by the Owl Shop after work today, a chilly late January Monday, with the Alec Bradley Nica-Puro Rosado Gordo in shirt pocket.  The cigar was a gift from my brother in law, Liam, who shares my love of cigars.  Liam and I have enjoyed several sticks together after family gatherings and the conversations have always been as good as the smokes.  Liam and I are both fans of the Alec Bradley line; I have never smoked the Nica-Puro before.

The Gordo is a hefty 6.2” 60 ring gauge cigar.  As the name suggests, this is a Nicaraguan puro – a Nicaraguan double binder and core of long-fillers from Nicaragua’s 3 main growing regions — Jalapa, Condega, and Esteli — are wrapped in a handsome Nicaraguan Rosado leaf.

Appearance is a nice oily chocolate brown, the Rosado wrapper is smooth with a couple of small veins and no seams.  Construction was very firm, with some softness noticeable just beneath the beautiful double-band.  The triple cap was impressive.

The cold draw was very flavorful.  Delicious notes of dried fruit, spiciness and some cedar.

The first third started off with strong notes of cedar, pepper, earthiness and some cocoa and nuttiness.  The burn was excellent, and a perfect draw.   The ash was salt and pepper and firm – and didn’t break off until about the inch and a half mark.

By the start of the second third, the flavor became creamier with continued strong notes of cedar, nuttiness and pepper.  There was a hint of leather and some cocoa.  The burn continued to be perfect throughout the second third.

Final third became creamier and the cedar and pepper notes continued right to the end and the burn remained perfect.  The cigar needed no touching up and never became bitter or stale tasting.  The smoking time was an hour and forty minutes.

The AB Nica-Puro was about as good as a cigar can be.  I would score it a 10 out of 10, a rating I don’t give often – but this is a true classic.

Recapping “The Glendon” RCA Victor Model 6-XD

At the 2018 New England Antique Radio Club Radio and Vintage Electronics Show, I had the good fortune of winning not one, but two door prizes!

The first was a circa 1955 RCA Model 6-XD-5A “The Glendon” AM broadcast receiver.  The radio was promised to be ‘operational’ but ‘not restored.’  The second prize was a coupon to WJOE Radio, a favorite local vendor for radio restoration parts who also attends the NEARC Show each winter. I used the coupon to stock up on a couple of capacitor assortment boxes realizing I could use the capacitors to recap the Glendon at some point.

That “some point” came just two months later in April when after listening to the radio for just about an hour and a half I heard a loud sizzling sound, followed by a loud “pop!” and then loud buzzing from the speakers.

Sure enough, upon opening the set up I discovered that one of the wax capacitors, No. C11, on the power line had exploded.

The failed C-11 capacitor.

A lot of folks are under the misimpression that when restoring old radios, the number one problem is that the old tubes have gone bad and that finding replacements is hard and expensive.  The truth of the matter is the absolute number one affliction that antique radios suffer is failing capacitors.  Replacement caps are plentiful, and inexpensive and many radios can be brought back to useable life by just recapping the set.

Over time wax and paper capacitors fail and the dielectric in large filter caps either dries up has leaked out.  A capacitor that fails appears in circuit as a resistor and will not block DC while allowing AC signals to pass as they should.  A sure sign that caps have failed in vintage radios is the presence of a predominant loud hum on the audio output.

Replacing capacitors is generally straight forward and easy.  It’s simply a matter of removing the old capacitors and replacing them with modern day equivalents.  Many times, you can easily read the values off the old capacitor once it is removed, but it’s also always a good idea to download a copy of the schematic and work from that.

BEFORE
AFTER

There are two values you need to be concerned with when replacing capacitors – the capacitance value and the voltage rating.

Capacitance is measured in farads – typically microfarads (MFD) or in picofarads (pF).  1 farad is equal to 1,000,000 microfarad, or 1,000,000,000,000 picofarad.

It’s always good to work from a schematic diagram – I found the schematic for this radio on the Radiomuseum.org website – the troublesome C11 is highlighted above.

When replacing capacitors, an exact match for the capacitance value is seldom critical, especially when working with consumer grade AM radio circuits.  If you are unable to find a replacement cap with the same value, it is generally o.k. to use a close or higher value capacitor in the circuit.

You can also combine capacitors together to create a capacitor with the proper value.  The math is simple – if you connect capacitors in parallel, their value equals the sum of the individual capacitors.

C1 + C2 + Cn in parallel = Ctotal

The second value you need to be concerned with when replacing capacitors is the voltage rating which is often abbreviated WVDC (working voltage, direct current) on the capacitor and on the schematic. Always be sure to replace capacitors with new units that are rated at the same working voltage or higher.

So, returning to The Glendon, I replaced C11 and all the other wax capacitors.  I noticed that the previous owner had replaced the electrolytic filter caps already.  The schematic called for a 30 MFD and a 50 MFD filter cap.  The previous owner installed a pair of 450 volt 47 MFD caps so I left well enough alone.

The “Dead Soldiers” removed from the set.

Sure enough, my recap job brought this fine old radio back to life and it spent last summer as my chair-side radio on the front porch for Red Sox games.  And what a year it was for listening to Boston baseball on the radio!

RCA VICTOR CO., INC. MODELN 6-XD-5C “THE GLENDON” SPECS:

Year: 1954/1955 
Tubes: 12BE6 12BA6 12AV6 50C5 35W4
Circuit type: Super-Heterodyne IF 455 kHz; 2 AF stage(s)
Tuned circuits:6 AM circuit(s)
Bands:  AM BCB only, 540 – 1600 kHz
Loudspeaker:  2 Loudspeakers / Ø 4 inch = 10.2 cm (not stereo)
Power out:1 W (1.5 W max.)
Material: Plastic
Dimensions (WHD): 12.5 x 7.5 x 6.375 inch
Antenna: Build in loop antenna
Power consumption: 35 watts.
Other: has audio input jack to connect Victrola record player.

©2019 JMSurprenant

Something new from AB1DQ

Hello and welcome to the new AB1DQ blog, I hope you find this site informative, inspiring and fun.

My name is James M. Surprenant and AB1DQ is my amateur radio call sign. I hold an Amateur Extra Class license and earned my first ticket as KB1IAR in 2002.

Although I came to ham radio later in life, I have always been fascinated with radio and electronics ever since I was a child ‘wasting time’ at my grandfather’s workbench.

My intent for this new blog is that it should be a place for me to share ideas of personal interest and projects that are currently on my workbench.

This is a personal site and like most persons, I’m not one dimensional. I have many personal interests including, but not limited to, photography, spirituality, cigars, whisky, baseball, poetry and music. Thus not all of the content here will be related to electronics and radio. I ask that all visitors here consume the content I share with an open mind, take what they need and leave the rest.

So, thank you VERY much for visiting – please drop me at ab1dq@protonmail.com and let me know what you think.

This “Cheshire Cat” is my ham radio logo and appears on my QSL card.
It was created by professional cartoonist and fellow ham radio operator N2EST, Jim Massara. Lear more about Jim and his work at http://www.hamtoons.net.

73 de AB1DQ
James
Cheshire, CT

Altar Q Cigar by Oscar Valladares

I smoked my first Altar Q cigar by Oscar Valladares a couple of weeks ago at a whisky tasting at the Owl Shop in New Haven, Connecticut.  It was my first cigar from Oscar Valladares, although I have been meaning to try their Leaf for some time.  The Altar Q impressed me with a lot of flavor that evening and I noted that it paired particularly well with the Laphroaig Lore Scotch whisky that was being poured.

It is noontime New Year’s Eve 2018 and I stopped in at the Owl again today to try another Altar Q. after running some year-end errands.

The cigar comes boxed in a wooden box of 16 with the cigars separated by paper. The cigars do not have a cellophane wrapper but instead have a beautiful wide 3.5” paper foot band honoring Mayan tobacco.  Currently Neptune Cigar offers the box of 16 for $168 which makes the cost of an individual stick $10.50 – a bit pricey for me, but really worth it.

Oscar Valladares Tobacco, is located in Danli, Honduras. It started operating on 2012, the Factory was founded by Oscar Valladares, Hector Valladares and Bayron Duarte, with experience in the tobacco industry; Oscar worked for more than 9 years with Rocky Patel and Bayron worked for more than 20 years for General Cigars and Oliva.

The Altar Q is a 52 ring gauge 6” cigar and features a Ecuadorian Sumatra wrapper, a Honduran Copan region binder and Honduran long fillers.  The appearance is oily and smooth, seamless with very few visible veins.  The cigar has a triple-cap and a pigtail.  Construction is fairly firm, and just a bit squishy.

I cut the cigar with my notch cutter and found the pre-light draw to be flavorful – very spicy, leathery, earth and classic tobacco flavored.

First third

Upon lighting, the Altar Q starts off with a big bite of spicy pepper – wow.  Also notable from the get go are subtle citrus, slight honey notes and some nuttiness.  The draw is very good and the burn is decent, a little uneven and required some slight touching up.  The cigar produces good smoke and produces a nice solid salt and pepper ash.

Second third

The strong pepper flavor is yielding a bit to a nice nutty and citrus flavor at the start of the second third.  The draw and burn both continue to be very good.  Just beyond the mid-point the flavor is becoming nuttier and the creaminess begins, however, the cigar needed re-lighting at this point, just as my first Altar Q needed a couple of weeks ago.

Final third

The last third begins with more creaminess, some nuttiness and the ever-present pepper.  The burn remained good and even and the draw was perfect.  As I smoked my way through the last third, the flavor became more and more creamy – a very tasty and satisfying smoke.

Overall

I consider the Altar Q an instant classic and a new favorite.   It pairs exceptionally well with a smoky peaty scotch such as Laphroaig Lore or a hot pot of Lapsong Souchong tea. I would rate it a 9 out of 10 and I look forward to picking up a full box before too long.

© 2019 James M. Surprenant