Back in the mid to late 80s I used AutoCad for schematics and even PCB design, before I migrated to Protel / Altium. I learned AutoCad using the command line when that was the only way you could do it. Much faster than dinking around with the mouse and menus.

You can create all your parts (e.g. valves) and save them as separate files (using the WBlock command) to build up a library that you can re-use in new drawings.

Draw the lines as Polylines (pline) and you can use the Stretch and Trim commands to move things around while they stay connected. Neat! Then use the pedit command to tidy things up.

Using the pline command you can make the boxes around the valves and round off their corners without having to use arcs. This has the advantage that it is a single object, there are no little dags on the joins and you can change the width of the line and join in arcs etc using pedit.

Make sure your snap is on and set to a workable grid, so stuff joins up easily.

Once I learnt these tricks it sped up the process no end. It was really good for moving stuff around on PCBs, although of course lacking the error checking that Altium gives you. The Offset command was great for making neat multi-track busses.

Sadly, I can now only run AutoCad on an XP machine that's somewhere in the garage. I now use Fusion360 for mechanical drawings and Altium for schematics and PCBs.

Fred, I think your circuit is about as close as we could get. And quite workable.

The R/C coupling out of the converter might have been a solution for our 6Y9 Autodyne reflex set.

Yes Ian. One IFT2 may have been a good idea.
The loss of selectivity losing the 1st IFT would probably not be much of a problem and would have made the chassis a bit simpler.

Carl will be able to assess what sort of performer his little guy is be compared to other sets.
All interesting stuff.
Fred.

Same issue here with the AutoCAD. Its a Windows 95 Version & is running on its own Circa 2000 XP OS computer. Here they are all in the Insulated shed.

Computers are not in the house here: They are in the same cave as the radio repairs, and farm office work station, in their own dedicated spot. For obvious reasons the main computer bench, rather than table, is 2m long by 1.8 wide. Homemade to take the weight of heavy printers & UPS, Engine etc., on the first 600mm of each end. The central longitudinal bearer has two legs 600mm (from the ends) which support the load bearing triangle: Six legs total and it will never sag in the middle. Brace for centre legs forms a 900mm wide lower shelf, in conjunction with the rear brace.

XP computer is more in keeping with rural traditional it's adapted onto a lower shelf with a strategically selected lump of 20mm by 120mm treated pine under the engine, propping up the shelf so it cant collapse it.

Marc

Fred in waiting for the Cabinet to arrive back here I have sat this little chassis in the kitchen on many occasions and found it to be quite a strong performer. Selectivity is great. Its only after 30 minutes of running that it has a very quick shift off station. I only need to retune and its fine again. I wonder which valve needs refreshing.

Most of the Pentagrids are voltage sensitive and until they are "warmed up" to operating temp they will drift upwards in frequency.

You could double check resistances as any getting hot, or perhaps drifted too far out of spec. never help.

Marc

Hi Carl, yeah like Marc says there may be either a design thing where a moving voltage shifts the oscillator frequency or a component drift with temperature rise.
I doubt the builder would have had the knowledge to balance temperature coefficients in the tuning circuits so the set may just have to stay as it is.
If you have the time you may like to play with "hot and cold" spray on parts in the tuning circuits especially around the oscillator to see if anything is sensitive.
Also you could try another 6K8.
Its no big deal if it warms up and then sits stable.
Fred.

My comment is based on that which is written in the "Radiotron Designers Handbook". 10th impression 1944. 6K8 is more of a SW tube. Fluctuations in the control grid voltage has a minimal effect on frequency changes and it is not as overly sensitive to AGC on SW (all frequencies) like many others e.g. 6A8 are.

AGC can cause flutter in 6K8; that will mean that the Oscillator Plate circuit may have an 8μF Electrolytic added.

If not mentioned. Metal 6K8 (that one) should have pin one grounded. That like Philips Metallised applies to most of them. But don't get caught out by the odd one that is different & its another pin.

Marc

My Major problem is I am colourblind. So working out values from the resistor alone is a night mare.

I don't know what it is, but with this computer, it sees the site as stable as a bucket of weeping gelignite, with fail to load fail to update & locking up?

My mother is a recognised artist & was colour blind in the pink area. Aside from road vehicle licences, I did train as a pilot & textile dyer. That means that I am not one of the 26% of males & 8% of females that do have problems. There were always dirty looks when, after spending considerable time trying to match a colour; I would turn up & sort it in minutes.

How do you go with the myriad of resistor colour charts on the WWW. Altronics has one in their data section.

Hi Guys (and Girls),

I have been following this thread with interest and just now have been checking through the RTV&H disc from Silicon Chip. April 1940 edition (page 27 to 37) has a Little General project very much like the one that is the subject of this thread. This one was designed by John Moyle.

Valve line up: 6K8G, 6G8G, (6B7S), 6V6G & 80. IF 465 kHz.

I'm not much of a tech myself so I've sent the schematic to our resident gurus to see what they come up with.

There were variants of the Little General. At one point I had, or was given circuits for them and others along the same lines. However, other than the computer, they may be in a filing cabinet.

It is in design, typical of the era. However, by now all of them at a minimum would need the paper and electrolytic caps replaced. Due to changes in descriptors, it is rare to see "surge volts (SV)" aka "Peak Volts (PV) on a modern electrolytic cap. The old Ducons were commonly 525PV which is hint to use 600V modern ones.

It is amazing how, when set up properly, how tubes can out perform mass transistors, in some areas.

Re post #86 here is my comment to mono about the original "LG" circuit.

Hi, yes its a very smart circuit arrangement.
I have the same SC disc with all the RH issues.
Also I have a big hand made book from my Father made in the 1950's that has a lot of these circuits pasted in.

Its very tempting to make up an exact copy of this set.
If I live long enough I'll make it a project to do!
Having made a couple of "little generals" as you know in Special Projects, but I have always used later ciruits.

Moyle makes a point about no AGC , BUT, there is a DC loop from the detector via the 0.5m leak back to the cathodes.
That intrigues me, should be a positive feedback not negative and cuse instability but who knows?
You can trial these things in PC programming but really the only way to trial it is to build and exact copy set and see what is going on.
He may have created a subtle gain boosting circuit without realising it.

Cheers, Fred.

I should CC this to Brads site.

Done!

A question because of my colourblindness ! The resistor on the 6K8! What is its value according to the schematic ( I cant tell you what pins as its too deep and entrenched ) ? I suspect this one is the issue and unless I bend the chassis up so I can access it it will be a issue to replace.

Hi , jeez colour blind!!!
I had an ace fitter working for me that quietly said one day, please check this switchboard wiring and tell me what the colours of the wires are? Seems all wires were shades of Grey to him! Best Diesel fitter I worked with and I had no problem double checking Red/Yellow/Blue/Green wiring for him. Being colour blind actually made him able to "see" things like oil leaks and hot surfaces better than full spectrum people like me.

Any way, there should be a grid resistor which was always 50k ohm, Green body/Black end /Orange dot or to you Grey/Grey/Grey!
Never needs replacing since the value is +/- 20%, just so long as it's not open circuit.
Just stick an ohmmeter on it 50 to70k will be fine.

Fred.