(Almost) The Last of The Mohicans

While I now tend to favour European transistorized radios made in the 1960’s and 1970’s, I can remember as a kid lusting after shortwave receivers like the Heathkit Mohican. Alas, the price was too high for a teenager with an allowance and no job, so I had to settle for a Knight-Kit Star Roamer at the time.

My Restored Heathkit Mohican GC-1A

Fast forward to last fall, and there was a sad (correction…pathetic) looking wreck of a Mohican GC-1A at a local ham flea market, beckoning to me. For $10, I thought I would take a chance on it, even though the S-meter and antenna were missing and the case and chrome knobs were badly pitted. One promising thing was that the dual sliderule dials were clean and intact, and the tuning knobs and pointers seemed to work OK.

First IF Transformer now shielded
and covering the hole in the board

Opening it up, however, revealed more surprises. There was the first IF transformer, sans outer shield, suspended by a few wires above a gaping hole in the board. Did something explode in there, or did the builder get frustrated and punch a hole through it with a screwdriver? Looking further down the board, I couldn’t help but notice a couple of trimmer pots, also suspended by wires above the board. This was going to require a schematic to figure out what was going on, so I Googled the manual and downloaded it.

Series-resonant 455 kHz filters
(circled)

As I was to discover, someone in their lack of wisdom decided to replace two interstage ceramic IF filters with those trimmer pots (!). But it doesn’t stop there. The AVC switch and the dial lights were also miswired. It dawned on me that someone with just enough knowledge to be dangerous must have had a go at this radio as a second or third owner, because the construction was otherwise  good. Maybe when they discovered that pots don’t work well as bandpass filters, they decided to take revenge on the IF transformer? While I didn’t have any three-terminal ceramic filters on hand, I did have some series-resonant two-terminal types that I used as interstage couplers in those same locations. Result.

Battery Pack

So, after sanding down the steel case, priming it, and applying several coats of an automotive aerosol paint (guesswork involved on the original colour), it looks great. Surprisingly, the knobs cleaned right up with a damp cloth, and continue to shine like new. Of course, the battery pack was somewhat corroded, but now functions well. With 8 C cells loaded, I have to say this radio weighs enough to make a good negative-buoyancy marine stabilizer (boat anchor), thanks largely to the steel construction.

S-Meter & AVC Switch

Getting original components is near impossible, so I settled on a replacement telescoping antenna, and had to enlarge the S-meter opening slightly to accommodate one from a cannibalized CB set. To make the meter function logically and properly, I had to reverse the scale card inside the meter and pad it down with a shunt resistor.

Apart from re-capping, one of the last tasks was alignment. Heathkit includes an involved procedure in their manual, and it’s worth following. The only oddity is that the IF tuned fine at 435 kHz, but I couldn’t get it to go to 455 kHz. This caused a bit of head scratching when it came to identifying the image frequencies, but as long as the alignment is done with this knowledge, it’s not a problem.

After completing the alignment, it was time to hoist the antenna and play. Intially, I was disappointed with the gravelly quality of the audio, and SSB sounded somewhat unintelligible at times. My first thought was that the IF alignment was poor and/or the BFO needed tweaking. With no joy there, I looked at the Mohican’s demodulated audio from my RF generator on the ‘scope, and noticed crossover distortion at the speaker. By padding the bias resistors on the bases of the push-pull audio output transistors, the sound is now quite sweet on both AM and SSB. It took a lot of padding, though, so the old germanium transistors were probably getting a bit tired.

Alignment trimmer caps and coils for local oscillator, mixer and front end

Heathkit marketed this radio from the early 1960’s up until about 1968. While it’s not the hottest receiver by today’s standards, it is surpisingly sensitive and stable. That probably explains how this single model remained popular througout nearly a decade. And while I lived with its challenges for several months, now that it is fully functional, the nostalgic value is going to keep it in my collection for some time to come.

Telefunken Bajazzo Sport 201

I’ve wanted to find a transistorized Bajazzo for some time, and while this one appears to be a ‘baby Bajazzo’, it doesn’t disappoint. The age range for this 201 is 1969 to 1972, but the Bajazzo name actually goes back to the early ‘50s tube era of Telefunken’s kofferradios.

Like a lot of radios from this age range, there was an optional car bracket which held the radio in place with a couple of threaded holes in the back and connected to the car antenna, speaker and power through a multi-pin socket in the bottom. I’ve never seen one, but it would have been a nice way to get shortwave and FM in the car back then. The AUTO button on the radio provides the connection.

Car Bracket Mounting and Connections

A feature I’ve never seen before in my other radios is a split medium wave band into two bands. MW2 is like a bandspread dial for the upper part of the band, and covers from about 1410 to greater than 1600 kHz. From the markings on the dial, it appears to be a part of the band occupied by specific European stations. It’s a nice feature to have, especially if you like to do some careful AM dx’ing.

Ok –now for some general impressions. It’s a very portable radio, and quite light even when loaded up with ‘C’ cells. Like most Telefunken radios from the early 70s, things got more plasticky. My main complaint is that the controls feel cheap, especially the tuning knob. It has a springy, non-precise feel to it and tends to overshoot when rotated. This means you end up rocking it back and forth to get exact tuning, particularly on shortwave.

Touchy-feelies aside, I find the performance of the radio very good. Sound is typically rich and bassy considering the size of the radio. Once again, for FM and shortwave bands, I compared it with my benchmark mid-to-late seventies Telefunken Partner 500. Right away, I noticed that the Bajazzo performed better than the Partner on FM. Better sensitivity, selectivity and lack of front end intermod distortion from overload were evident. The AFC does an amazing job of finding and locking in stations, even a MHz or so away from where you’re tuned.

On shortwave, the comparison was not as clear cut. While the Bajazzo was physically easier to tune, the Partner actually beat the Bajazzo slightly in sensitivity, to my surprise.

Just about every radio in this category that I’ve tested in North America was utterly useless on longwave. This Bajazzo is an exception. While sensitivity was not hot on this band, at least AM band feedthrough was only noticeable below 200kHz, and even then was minimal. What was a pleasant surprise was that I was able to receive a number of aviation NDBs (non-directional beacons) in the 200-330 kHz range, some as far away as 300 km.

On medium wave (AM) the radio did not disappoint either. Both MW1 and MW2 performed well. This may be partly due to the extra long ferrite bar that holds both the AM and longwave coils. More ferrite core means greater signal capture, and probably explains the reasonable performance on longwave too.

Frequency coverage is as follows-

·         Longwave: ~150 to 350 kHz

·         MW1:  ~520 to 1450 kHz

·         MW2: ~1410 to 1630 kHz

·         Shortwave: ~5.8 to 12.5 MHz

·         FM: ~88 to 108 MHz (North American model)

Power Requirements-

·         7.5 VDC external; 6 ‘C’ cells internal

Line In/Out (TA/TB)-

·         Through standard 5 pin DIN jack

·         Selected by pushing LW & KW buttons simultaneously

Antenna –

·         Internal telescoping & external via side panel Motorola-type jack

External Speaker -

·         Via side panel jack

NORDMENDE GLOBETRAVELER II

I like Nordmende. Their radios just seemed to ooze quality. The Globetraveler series exemplified that. It is the epitome of what was considered a high end portable radio in the late 1960s: well built, beautiful sounding and feature-laden.

Nordmende Globetraveler II

At the time, the Globetraveler would have been way out of my league in terms of affordability. Besides, I was just a kid then. Today, however, a gently used version can be found online quite cheaply. With a little bit (hopefully) of effort, it can be made to look and run like new.

Such is the case with my Globetraveler II. It's the North American equivalent of the European Globetrotter TN6000. Its best feature is a bandspread tuner that allows you to tune specific shortwave broadcast bands individually and comfortably without the "touchiness" of a tuner that covers all bands in a single sweep of the dial. These bands range from 13m to 80m. Not sure why they included an amateur radio band, because as far as I know, broadcasting never took place in the 80m band.

 

Besides the need for cosmetic cleaning, here were the issues with mine:

• Shortwave bandspread tuner non-functional on some bands and band switching was noisy. This was major for me, as the bandspread tuner was what set this radio apart from many others.
• Audio was slightly distorted (crossover distortion).
• The a.c. socket uses a silly switch that cuts out the battery when an a.c. cord is plugged in. Silly because the lever that actuated the switch often stuck, cutting out the batteries even when the cord was pulled.
• Power supply needed re-capping. No surprise there after 45 years, but ripple persists. Since I prefer battery power, this is not a big deal for me, but I suspect a leaky diode or two in the bridge rectifier. Later.
• A dangerous carry handle that likes to unhook easily on its own. Caution with this one!
  

The bandspread tuner was not an easy fix. The first approach is always to try to clean all switches. I used a run-of-the-mill switch and potentiometer cleaner on the tuner's wafer sections. Big mistake. The tuner became less and less functional the more I sprayed until it totally failed. By this point, my mind went straight to the hardest solution, and I began to believe the local oscillator stage failed. The thought of accessing this tiny board gave me a slap of reality, and I bit the bullet and bought a decent but expensive cleaner (DeOxit). A couple of sprays later, it came back to life. The wires in this tuner are very delicate, so after I discovered a wire I had broken when probing the tuner, all bands worked again. After the cleaner dried, I re-tuned as many coils as I could access. This tuner is designed for manufacturing, not service. Access to components is sometimes horrible - a nightmare in fact (see photo).

Bandspread tuner from hell

Fixing the audio issue was easy. De-solder a jumper, insert ammeter, and tweak the output stage bias until about 6mA is achieved.

Finally, as with other radios reviewed here, I performed a subjective comparison with my old stalwart kitchen radio - the Telefunken Partner 500.

First off, I must say that in terms of sound quality, the Globetraveler is in a different league due to its size relative to the Partner. No surprise - the bass presence is noticeably better on the Globetraveler. Another advantage it has is separate bass and treble controls, compared to the Partner's tone control.

In terms of FM performance, the sensitivity was only marginally better on the Globetraveler. In urban areas with telescopic antenna up, both radios suffered from overload. This resulted in distorted images of strong stations appearing in other places on the dial, interfering with weaker stations.

With the antenna up on the Globetraveler, it was noted that on certain shortwave bands there was some feedthrough of FM signals. I suspect this wouldn't be a problem once outside of town. Interestingly, the Globetraveler has a segmented antenna, giving about an extra foot if needed in fringe areas. Comparing the two radios on the 19m and 49m bands, it was hard to tell if there was a difference in sensitivity. The difference, of course is in the ease of tuning in stations with the Globetraveler's bandspread tuner. I also suspect (but have not verified) that the Globetraveler has better image rejection due to its more sophisticated tuner with separate front end tuning coils for each band.

The Partner holds up surprisingly well against the Globetraveler in terms of basic performance, but the Nordmende definitely is much more pleasurable to use and listen to.

Some other Globetraveler features to point out:

• Sensitive tuning meter on all bands.
• Inclusion of a Marine Band (1.5 to 3.5 MHz), although it's not used much for this purpose these days.
• Long wave band, also useless in North America.
• AM (BC) band, which uses an internal loopstick antenna.
• External antenna connection, which helps shortwave performance significantly.
• Operates from 5 "D" cells (7.5V).

The Globetraveler II is definitely the flagship of my "kofferradio" fleet. Can't wait for warmer weather to take it outside and test it outside of the city.

GRUNDIG CONCERT BOY 1100

I recently took a chance and won this radio at an auction; untested, with a seized tuning mechanism and coated with nictone.

When I got it on the bench, of course, it was totally non-functional. A little probing revealed a shorted filter capacitor in the power supply, which prevented it from working from either AC or batteries. A higher voltage and capacitance-rated part fixed that.


As for the seized tuner, I didn't have a clue what was going on. Thanks to the Internet and Google, I found that this was a common problem on Grundigs of this vintage ('73-'78). Apparently, the grease in the tuning capacitor hardens over time. One suggestion, which worked well for me, was to gently heat the capacitor with a hair dryer until the grease melted, then wash it away with a solvent like lighter fluid. I then re-greased the gears and pivot points with lithium grease, being careful not to get it on the plates. Result.

An unknown knucklehead who owned it before me decided that the headphone jack on the back (which works perfectly well) was not good enough for him. So, he proceeded to drill a hole in the front of the unit, just above the "G" in Grundig, and mount his own jack. The jack's now gone, but the hole remains. As for the nicotine...well, it's gone too, thanks to Windex and paper towels.

Concert Boy Goliath (left) and Partner David (right)

Since I've had my Telefunken Partner 500 for many years and am familiar with its characteristics the most, I will again use it as a benchmark. It seems like an unfair comparison when you look at the relative sizes of these radios...like David versus Goliath. But David puts up a good fight.

Right away, not surprisingly, the difference in bass presence goes to the Grundig. While the Partner's bass response for its size is excellent, physics says the bigger box is going to win. This Grundig big boy comes in at a whopping footprint of 41cm x 22cm x 10cm (approx.) [about 16.25" x 9" x 4"].

The Grundig's communications receiver - style tuning knob 

With telescopic antennas on both radios retracted, it was evident that the FM sensitivity of the Concert Boy was also better than the Partner's. In an urban area, the Partner gets overloaded easily, so lowering the antenna is required to prevent "ghosting" and distortion. The Grundig handled this proliferation of FM signals better, even with its antenna fully extended. Another point for Goliath, but his luck is about to run out.

Switching to the shortwave bands, the Concert Boy was almost useless on its K2 band (SW2 - 6.1 to 18 MHz) because of extreme feedthrough of local FM signals clobbering the weak shortwave signals. While the Partner had no such issue on the 19 m band through to the 41 m band, when a shortwave signal was heard on the Grundig between the FM splatter, the Grundig was slightly more sensitive.

That gap was closed at the 49 m band, where the sensitivity of both radios seemed comparable (on a subjective basis - not measured), and the FM interference on the Grundig subsided somewhat. One advantage the Concert Boy has is a second band (K1 or SW1), which is a bandspread band for 49 m (5.9 -6.23 MHz). While this makes tuning easier, I still find the tuning mechanism somewhat stiff, yet springy and imprecise. More heat and grease needed, perhaps?

Testing longwave here in North America is pointless, so I'll discuss AM performance. The same FM feedthrough problem exists on the Grundig if, for some reason, you leave the telescopic antenna extended. Since the AM band uses the internal loopstick antenna, keep the antenna down when listening to this band. Otherwise, the Concert Boy once again becomes useless.

If you live in a fringe FM area, the Grundig has terminals on the back for an FM dipole, as well as a DIN input/output jack and a headphone jack. The Partner has the latter two only. Note that the antenna terminals are only for FM and will not improve shortwave performance.

I have to say that I think Grundig's engineers got a little lazy on this one by providing themselves with tons of room to stuff their electronics into, while not taking advantage of it to enhance front-end performance. This radio suffers badly from cross-band interference. If you want a room-filling kitchen radio for FM, though, this one may fit the bill.

The big Boy needs big batteries : 6 'D' cells

NORDMENDE TRANSITA DELUXE

Radio makers tended to use the same model names over several years, while making significant design changes along the way. This is no different from the auto industry. A Toyota Camry, for instance, evolves in looks and features throughout the years. This applies to the Transita, the Telefunken Partner which I recently reviewed and probably every other radio produced in this era.

The Deluxe version of the Transita shown here was introduced in the early 60s, and is based on a wooden case covered with leatherette. This particular model covers the AM (medium wave) band, shortwave from 49m to 25m (~6-12 MHz) plus FM. The rounded profile gives it a charming retro shape. Later German radios became more squared off.

External connections include a Motorola automotive-type external antenna socket on the right hand side, and 9 Volt DC power input and headphone jack on the left. I didn't have much luck forcing a Motorola plug into the socket, because the chassis seems to be misaligned with the case.

A 6-cell C-size battery pack attaches with two snap connectors. As can be seen from the photo below, the back cover can be conveniently separated from the radio by unplugging the telescopic antenna's banana plug.


In this post, I will compare (subjectively) the Transita Deluxe with the Telefunken Partner 500.

I complained about the sticky tuning mechanism on the Partner. The Transita feels lovely and smooth in comparison. Despite that, on shortwave and AM, the Partner comes out somewhat ahead. The sensitivity (again, not measured, but subjective) is lacking on the Transita, as I found myself cranking the volume to near maximum when trying to find stations. Once I found a strong station, another Transita shortcoming appeared: apparent lack of automatic gain control (AGC). Because of this, I found myself jockeying the volume control every time I tuned in stations of varying strength.


From a sound quality standpoint, the Transita definitely was clean and generally sweet. The Partner, however, once again had the edge by offering more presence at the bass end. As opposed to the continuous tone control on the Partner, the Transita uses a switch, which introduces a single heavy-handed treble rolloff preset when pressed. I suppose a simple lower value capacitor swap in the tone circuit would improve it, but currently this is one feature I can't ever see using. 
 
The comparison of FM performance, however, was a little less black and white. While the Partner had apparently better sensitivity, in a crowded urban FM spectrum, this proved a slight disadvantage. I found the Partner subject to intermodulation (IM) distortion, which means it was overloaded with too many strong signals. This results in stations appearing like images in multiple places on the dial, and generally with distorted audio. This is different from the 'images' you would get on shortwave, because the higher I.F. stage frequency of 10.7 MHz on the FM band is generally effective at rejecting images. Retracting the telescopic antenna somewhat helped act as a front end attenuator, but then weaker stations get lost. By default then, the Transita makes a better big-city FM radio (sound quality aside), but the Partner would excel in rural fringe areas.

Performance aside, the wooden case and the retro curves make the Transita Deluxe a nice decorative element for any home with mid-century décor. While radio performance improved in later years, the plastic-fantastic housings they evolved into didn't carry quite the charm that this radio has.

Introduction

In this blog, I will be highlighting mostly portable radios built in Europe & Scandinavia during the 1960s and 1970s. These were referred to in Germany as "kofferradios" or suitcase radios because of their boxy designs and carrying handles.

Why these radios, and why from that era? First and foremost - big sound. The large size of these units meant that they could employ hefty speakers and provide a reasonable baffle for them. This resulted in sound that rivalled bookshelf speakers from that period. Kind of like a Bose tabletop radio before its time.

But there is another reason. At that time, shortwave was still a plentiful source of international and domestic broadcasts, so most radios had at least one shortwave band. FM was experiencing a swell of popularity, so it was included on most models too. And, of course, AM (or medium wave) was another band that was standard. Long wave, used mostly in UK and Europe but not North America can also be found on just about every model.

This combination of bands in one portable has disappeared in modern radios and mp3 players, so the kofferradios have become popular again for nostalgic reasons. Those features also make them collectible.

My interest at this time is only in transistorized radios. The intent is to show photographs of any radio that I can buy, borrow or restore that meets this criteria. Whenever I have researched radios online, I have often been disappointed by the lack of some of the most basic information a buyer would want, such as: what frequency range is covered on shortwave?; what is the shortwave performance like?; how good is the sound quality?; etc. I hope to remedy that in this blog by making those comparisons where appropriate. I will also stray from time to time and present European 'kitchen' radios and component receivers as they become available.

So here we go.......