Sorting this set out into a working model was an interesting process.
There were lots of lessons in doing so.

There were a couple of questions not resolved that some of the more experienced people may be able to answer, like:

Who made it?
What year is it.
The padder connection to the mixer cathode.
Why does it have wooden cabinet, not Bakelite.
The use of wire wound bias resistors in the mixer and IF cathodes.

Just on that last item, maybe just what they had, or, maybe subtle feedback?
Even though the cathodes are bypassed with a .05 paper cap, that means little at RF.
There is measurable RF level at that capacitor, having a fair amount of impedance at RF.


Cheers, Fred.

Joe's Little General Radio

Yeh! I was not joking, re wire wound resistors and RF: They with a cap can form a tuned circuit. Some radios were actually made with a deliberate amount of regeneration.

With some cranky sets, I have done the screen grid (autodyne) thing, where they put an RF choke at the audio amp / plate detector. Some tubes are just not fussy about what they amplify and some fall foul of that. If too much RF gets into an audio, with not fussy tubes, they will amplify it and can / have cause/d all sorts of instability.

Why does it have wooden cabinet, not Bakelite.

The use of timber for mantel models had all but passed us by in the late 1940s but there were a few exceptions. AWA made a timber version of the 500-series Radiolette. Airzone made a timber version of the almost equally popular Cub. Airzone even did a badge-engineered version of the Cub for its sister brands, Peal and Malvern Star.

UPDATE: On that note, I have a sneaking suspicion the chassis was made by Airzone. The power cord is in the same place and the physical component layout on top is very similar, including the silly location of the power amplifier.... why put a valve with nuclear-level temperatures inside the radio? It would surely be better located next to the rectifier, where it can get maximum heat dissipation, surely.

I sent a 1947 HMV 847 back to Tocumwal a few days back, & it has a wooden cabinet.

There were & still are those that go to incredible lengths to put stuff in unimaginable places. There are quite a few plastic sets where the hot tubes are too close to the cabinet and that damages it

On some sets people put the long envelope dial lamps in sets with cellulose dials, instead of the small round lower wattage ones and wonder why they burnt a hole in it.

HMV 42-71: Rectifier, Output & Det/ first audio. These so close to the open sided transformer that they baked the wires & wrapping of that side of the transformer. After splicing in new wire, I put a heat shield between them & the transformer.

American Midwest. Reasonably ineffective Faraday cage with audio wires in front of it where its open & running wires carrying RF through the audio. Then you wonder why there is RF in the Output tubes, which they can amplify. That sort of caper can also put the tubed in an AC magnetic field.

One often wonders how much was to look pretty rather than practical.

Maybe the transformer could be turned through 180 degrees so that it doesn't touch the valve, or maybe the transformer brackets bent to create a gap between it and the valve.

The idea with the metal plate on the 42-71 actually as a heat shield, heat sink and to a point a flux shield. Another option by way of a quasi heat shield, is a chimney. Its transformer is rectangular and it is impractical in its case; You have limited height to raise it.

Having designed a fair amount of equipment I can look at a little set like this and smile.
Design of something be it a trench digger, a toaster, a car, whatever is a wholistic thing aiming toward a set of targets.
The targets are a mixture of expectations, marketing and business priorities.
This little radio had a couple of targets, tune in radio stations and be cheap.
Long term reliability and technical niceness were not targets!
But that's ok because a set like this fulfilled the market expectation.

Having lived and died by what I produced I can see the problem from all sides.
Back to the practical side, this little set was a real 'little general' and put together to work with the minimum number of parts.
That the red-hot parts were jammed in next to things that can catch fire had no import to the builder.
Perversely, the rectifier heating the power transformer and the output valve cooking the output transformer mat actually be saviours!
One of the killers of those winding is moisture ingress.
Having built in moisture heaters has cancelled that problem!!

In case that is not clear I have built equipment that required actual heaters to be included to prevent collection of moisture and failure.
This set has them built in already. A bit tongue in cheek but there you are.

The owner and I talked a bit about the cabinet and the penny did not drop at the time as to why the cabinet was 'damaged' at the top.
It's obvious, no ventilation, trapped hot air and radiant heat, the cabinet is slowly charring at that point by the 6V6!
What it needs is a whole lot of holes in the top to let the fire out.
Not a sales feature!

Any decent designer would have made the set bigger, provided ventilation or (as Marc C says) laid out the valve so the hot bits were at the very back. but then the set would have cost more and worked no better anyway. If they even though about it.
My scratch-built sets always are a bit bigger than they should be because I would leave some flow room above the valves, put slots or holes to get flow through etc.

As for the design elements under the chassis, hey it works and lots of money was saved by not putting in bypass capacitors and using whatever parts they could lay their hands on at the time, I suspect mid 1940's when the whole country was producing for the war effort not the civilian market.

The IF valve is interesting, I suspect the chassis was made for a side pin valve EBF2. The actual valve used is an octal EBF2-G.
The EBF2-G octal does not exist in a lot of valve manuals but it's in the chassis!
Joe and I got mightily confused at first when I was checked the pin layout and wiring.
Just another little anomaly due to war time production conditions.

Cheers, Fred.

Fred, your comments about design retrospectives resonate.

As a designer who still makes a living from doing it, I also find looking back at such design cases instructive.

A definition of quality I heard many years ago is that it is a measure of how well a design or product meets its targets and end-user expectations.

It's often a case of "why did they do it that way? Ah, I see!"

But sometimes really dumb design mistakes occur that make it through to production. In one famous case the refusal of the chief engineer to admit he was wrong led to him moving on - and taking a public service job!

...and taking a public service job!

Where his lack of thought and experience would probably have been more appreciated, given that the 'shareholders' (us taxpayers) would be hidden from view and his on the job performance would be covered up. In such cases, bosses who take on workers who don't do their job correctly are known to move on themselves rather than show the strength required to sack the worker. I've seen that happen in the public and private sectors. I make it easy for myself - I get rid of the worker and don't let someone else inherit a disaster I helped make.

I am the chief engineer where I work and I'd like to think I am a fair boss to those who do well in their roles but I do live by a simple motto - I am not a train driver, so I refuse to carry passengers.

The nitty gritty in design can be difficult but the basics are easy, with some experience and also listening to what others have to say or borrowing ideas from a similar product. Plagiarism is very much talked down but let's face it, to a degree everyone does it. There are only so many configurations, layouts, ways to expel heat, ways to waterproof, etc.

Even though he's passed away I don't want to identify the guy, largely because he was a genuine genius. He created a large body of work related to mathematical modelling of design, much of which is still relevant today.

Guess he just didn't like admitting he made a mistake by making an assumption without checking it. Or maybe he just didn't check the work of a junior engineer, we will never know.

Either way, the mistake was expensive for the company and the reputation of its products. It teaches valuable lessons for all engineers.

You have heard of him and he got a gong.

It is amazing as to the ramifications simple errors can have. Someone came up with the bright idea in the chemical factory, that electricity could be saved by shutting off one of the cooling tower motors, when there was no major load.

The pumps were in parallel. The lunch room was near the pumps and I just happened to be there when one motor decided, with appropriate acoustics to fail. I went out to isolate it hydraulically and tag it off.

This is when I realised the dangerous error: It was running backwards? Somehow the system had never in its life, from day one, ever been checked for a motor failure. The motors formed a closed loop and hydraulically coupled.

That, because there were no one-way check valves, due to that major oversight, it meant that the plant lost all cooling on the chemical reactors.

Hi Fred,

Thanks again for your time and expertise in getting the “Little General” back up and running. I honestly wasn’t expecting you to take it on, but after seeing how much I had to learn, it was clear I was out of my depth. Your willingness to help, especially with a delicate radio like this, was much appreciated.

The repair in Special Projects that you shared was really informative. It’s not often you get that level of detail after a repair, and it definitely gave me a clearer understanding of the process and some troubleshooting techniques. I learned a lot, particularly from how you methodically diagnosed the problem. From checking the local oscillator’s role to troubleshooting the mixer and IF stage, it was clear how much expertise you brought to getting the “Little General” working again.

As for its journey, it’s certainly been on quite the adventure—especially considering it’s approaching 85 years old. First, it was bought and transported home in a backpack on my e-bike, and despite that, it survived and still worked. Then, after it stopped working after I poked around, I brought it to you for the repair, also in a backpack on my e-bike. Finally, after you worked your magic, I made sure it was cradled carefully for its 30km trip back home. It’s clear this little set deserves some extra attention.

Thanks again for everything. I really appreciate the work you put into this

It just goes to show how much time has passed us since radio collecting became more popular. When I started, around the end of 1988, radios could be had for a few bucks and few people took the task or the potential for radios to be worth more money very seriously.

But more to the point, when a radio was found, it was safe to just take it home and plug it in. Because of the much younger average age, the chance of running into a working set was a lot higher than it is now. These days, even the youngest valve radios should get the once over, like what happened here.

A good result has come about on this occasion - great to see.

Hi Fred,

Radio, Television and Hobbies (predecessor to Electronics Australia) March-May 1961 describes a mantle radio called the "Little General for 1961". 3 valves 6AN7, 6N8 and 6BM8. It has a timber case, oresumably this is easier for the home constructor to make?

Does that match yours? I have April and May issues but not the previous. I can scan and link a copy for you if that is useful?

regards,
Glenn