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 Fred Lever's '1946 Little General' for 2017
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 Return to top of page · Post #: 1 · Written at 7:19:43 PM on 4 January 2017.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Here is my version of John Moyle's Little General as it may have been made in 1946.
I have pretty much scratch built the set using as many 1940's junk parts as possible.
I have put a lot of detail into this as there was a lot of fixing and refurbishing to make parts work.
I've included a parts list and a general guide to what I think could constitute a Little General's parameters.
I hope this encourages other enthusiasts to make their own version and detail what they do.
In making the set I carried out a lot of testing of components and performance testing which is all pretty basic stuff that the experts may roll their eyes a bit about. I'm still learning!
Please comment / criticise / applaud as you see fit and i'm happy to answer any questions about the build or the article.
Enjoy.

Fred.

A 1946 Little General for 2017


 
 Return to top of page · Post #: 2 · Written at 9:09:08 PM on 4 January 2017.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1074

A lot of work went into that project. Congrats on getting it to run properly.


 
 Return to top of page · Post #: 3 · Written at 9:28:07 PM on 4 January 2017.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 5505

Good article. A goal of mine for many years has been to make a Little General. It has been said in many places that the Little General was Australia's most popular valve radio, smashing sales of popular mass-produced radios of the time, such as the AWA Radiolette and Astor Mickey - not an insignificant effort for a kit/home-brewed radio! The fact that people are still building the Little General from scratch today truly takes its place in the nation's DIY spirit.

So... here's my new year's resolution - to find some time to make a Little General. Smile


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 4 · Written at 11:33:47 PM on 4 January 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5262

Excellent work, Fred. You'll have to put all of these great project articles into book form one of these days. Maybe via Lulu or similar.

Among my to-be-restored stuff I have a Little General that appears to be in pretty good condition. I haven't yet spent time to work out what year model it is.


 
 Return to top of page · Post #: 5 · Written at 4:52:09 PM on 5 January 2017.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 377

Wow ... excellent stuff Fred ..... you are to be congratulated ... a pity that you don't live in my neighbourhood .... I would be looking over your shoulder often .... Smile

A couple of comments/questions if I may ......

The Oscillator capacitor gang / padding issue .... rather than using a large 'padder' cap to achieve tracking, is it technically feasible to short out (or remove) a vane or two on the ganged capacitor?

Cutting down the IF coils for the Oscillator coil .... clever idea .... instead of using the 2 'series' coils and separating them etc .... would using the 2 inner coils (of the 4 coils) be better??? .... much lower coupling maybe a benefit .... if there is still sufficient coupling to drive the circuit ....???

IF at ends of Band .... I was going to suggest widening the IF bandwidth if you had sufficient amplification by adding some R across the LC tank ... but the end result appears fine.

Where is the 'test point' for Picture 49 DeMod audio? Not sure that I understand it.

Why is there a difference with 50Hz Hum when grounding Heater pins 2 or 7?????

What is producing the extra 'humps' on the Oscillator sine wave at the Plate, Picture 43 ????

Lastly, where do you get the time to do all this work???

Cheers,
Ian


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 6 · Written at 1:49:14 PM on 6 January 2017.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Hi, yes GTC I actually have the projects dumped onto a CD and may do the work and turn that into an indexed set of articles. I could then burn discs and have it as a "book" I could sell. I'd have to charge for it to pay for the discs, ink etc all this costs money and i'm a pensioner on a dwindling income. ( and malcom- harbourside- mansion just cut my part pension thanks for that mate i'll remember that one for later.)

I actually have been selling a book on Australian coins for about 10 years, I self print and distribute through a coin agent. Selling a book on a minority subject is regarded as a hobby in this country you have no hope of making any money, its all outgoings. My coin book has to retail at around $50 just to pay all costs and it's a fred- print, spiro bound effort that has a bundled CD with about 100 articles on coins. I could do a similar thing with the radio stuff but are radio people going to be happy to shell out $50 or more for an amateur effort? To contain costs I would make a mini book A5 size with the indexes and a bit of talk and then burn the rest on the CD and its still going be $50.

Ian, good tech questions!

1/ yes I could take the Dremel to a gang as I did making my FM tuner elsewhere on this site. I would pull the rotor out and cut vanes out until I got the PF value down. I stuck with the padder to save time and also give me 3 things to twiddle, the core, the trimmer and the padder to shuffle the resonant point about.

2/ I'm truly a "blind Freddy" when it comes to coils. I have little idea how they actually work, that is i'm well aware of the huge amount I don't know! It just seemed to be logical to prune the turns to get the resonance up from 455Kc with a 70pf cap to 500/2000Kc with a variable 30/450Pf cap. I guessed the primary and secondary should be within the length of the adjusting slug apart and made it so. No science there, just monkey see monkey do.

3/ Yes good point on the next project ( A Hi Fi TRF set with a row of 6SK7's and a PP 6V6 OP) I may look at what happens when you damp tuned windings as you suggest. With my little wobulator I can do experiments "hot" an see the results as I do it.

4/ The TP for that wave was the bottom of the 2nd IF secondary and C12. That's the clipped off (rectified/demodulated/whatever you call it) AC audio wave but still with lots of RF clinging on. The R/C network after that point rolls the RF off and out pops the AC wave only but still superimposed on a DC pedestal. You then lop the DC off with a coupling cap and then audio is ready for the next grid as in the next photo.

5/ I cannot remember exactly all the ins and out. The heater to cathode relation is not symmetrical and AC can transfer to the electron stream and wobble the plate around. Some one will know exactly what the go is. I know in high gain guitar amps I had to run the valves with DC on the heaters, OR, put a centering pot across the AC to the ground point and sometimes apply a bias DC to the floating heater chain as well. That's the "hum pot" you see at the back of a valve amp or test gear.

6/ The oscillator plate has harmonics in it because it is not resonant at that tank tuning frequency. It is assymetrical because of um uh oh something to do with how the valve works and saturation and cut off and um, ...... well. there you go! The grid circuit is the resonant tank and harmonics are damped in that circuit half of the coil. Mind you the things are still there but um suppressed um....my coil theory is not good! If the tank circuit was lumpy THEN I would be worried and have to learn a bit more about coil theory

7/ I don't have enough time to 1/2 the things I want to! But at least being retired I can CHOSE which panic I can play with and sit down like that LG set and spend a couple of hours in a day fixing a coil or a speaker or drill some holes before I have to race off the hospital or the docs to check the latest health drama. That what 70 year olds do mainly, skid from one death defying event to the next!

Cheers, Fred.


 
 Return to top of page · Post #: 7 · Written at 11:45:01 AM on 7 January 2017.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 377

Hi Fred,

Re 2/. ..... me thinks that Freddy ain't so blind .... Smile ... modest and very practical .... your reasoning seems quite sound to me.
It is very easy to get totally lost when reading about coils and how they function, particularly in resonant circuits and coupled resonant circuits.
Basically, coils store energy of a changing current in a magnetic field. If this magnetic field intersects another coil, it induces a changing current in that second coil. Same basic principle for all transformer type circuits, power, audio, oscillators, IF etc with a multitude of variations depending on the requirement.
The amount of energy (signal) transferred from one coil to the other dependes on many things, but primarily the distance between them as the magnetic field decreases with distance. Assuming that the axes of the coils are aligned, then the closer the coils, the more signal transferred. However, there is an optimum distance .... too close and 'nasties' can occur ... (to do with coil no. 2 inducing signal back into coil no. 1 etc etc ... all too complicated for me). This is referred to as 'over' coupled. Most circuits function properly in the 'under' or 'loosely' coupled configuration where the primary signal is dominant.
The slug is simply a method to concentrate the magnetic field which increases the L of a coil .... screwing it in and out provides a variable L.
With your oscillator coil(s) ..... I was wondering if the coils were too close ... hence, over coupled ... producing nasties....? This is only a guess ... and your tank oscillator signal does look okay .... and I am no expert on oscillators ....
However, if your interest is piqued .... or you have nothing better to do .... or you want yet another 'control' to experiment with ..... Smile Smile .... you could modify the oscillator coil(s) by rigging up some method to be able to slide the coils to change the coupling ... be aware that a change in coupling will also change the frequency, so you may need to tweak the slug to get back to the required frequency .... small steps for a start ...
Or you could simply enjoy your fantastic Little General as is.
Good luck with the health issues ...


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
Cheers, Ian

 
 Return to top of page · Post #: 8 · Written at 1:40:14 PM on 7 January 2017.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Thanks Ian i'll definitely do some work on coils. I need to sit down with my books like Scroggie on coils and my Radiotron Designers Handbook and be a bit better informed.

In my proposed TRF HI FI radio I am going to need 3 tuned circuits so need 3 RF coils.
(i'm having 3 tuned 6SK7, 1 untuned 6H6 detector/AGC, 1 6SJ7 tone control/volume, 1 6SN7 phase splitter, 2 x 6V6 outputs. I always saw Superhets as the hard way of tuning and demodulating an AM signal. Experts tell me how hard it is to get 3 or 4 gangs to track on a TRF but that's exactely what you do on a Superhet except one of them is spanning a different range ratio for the osc and NEVER tracks exactly! So you have an IF frequency "walking about" as you tune and all sorts of sproogles and whistles generated by the oscillator that need filtering out! Yes I know, there are no wide band HIFI AM signals available in Sydney except maybe for 2CH but humour an old man! I will need to have variable selectivity as in this area I am adjacent to the old 2WS site now 2RPH and that comes blasting through anything.)

I have this box of discarded IF trannys so guess what? YES! Flushed with success with the LG osc coil why don't I just take a 455KC/70pf IF plate to grid tranny and unwind the grid coil to resonate at 500/1600KC with a 30/450pf condenser and unwind the plate coil so it self resonates above the tuning range, maybe resistor loading to flatten the response, and produce a RF coil. After all WHAT COULD POSSIBLY GO WRONG?????!!!! Probably just need one slug to couple the 2 together and jog the L around.

Stay tuned, Fred.


 
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