Hi All, I have completed the project, wood bashed a little cabinet up and fitted the chassis in.
The part 3 has a description of the process, the final circuit used and a critique with the design short comings I can see.
There may be some among you with more valve knowledge than I that can comment on the Pentagrid type 6CS6 I used as apposed to the normal 6BE6. The 6CS6 appears to have been designed as a TV sync clipper/amplifier and I may have been pushing my luck using it as an oscillator/convertor!
I do not mind in the least any opinion or observation on the subject from anyone, particularly from any X radio/TV service people who had practical experience in the field, I am only guessing so even if you box me around the head it does not matter.
I will forward the usual PDF to Brad, who, with cutlass between his teeth fending off the pirates trying to board the ship, may be able to post it up.
Fred.

Little General 1976 - Part 3

The 6CS6 is a sync separator, both control grids a sharp cut off So with mixed results it may work, as you have found, similar to 6BE6 even that its construction is not the same.

Franks electron tube pages has them listed. http://www.tubedata.info/

Marc

Document uploaded.

Thanks Marc, the oscillator runs strongly and that is clear from the waveshape but the mixing gain appears to be low and I would have to do a lot of research into the actual levels of modulation of the stream by setting up a lot of tests and as usual I am over the project!
I am clearly using a tube with unsuitable slopes, as you point out they are sharp cut off so I bet I have clipping (gee fred you are a genius, that's what a sync clipper does!!!) of the signal giving a low gain situation.
When I get back around to playing with it i'll do some back to back tests with a 6BE6 and see how much better it can be if I use the correct valve.
Fred.

I would think pin 7 has to be the signal grid with 6CS6 I know IBM made a modified version of 6BE6. My thought is that 6BE6 may be similar to 6SA7. With it one forgets everything they know about Pentagrids as it has a suppressor grid and no true oscillator grid: It is very different & behaves that way.

It is therefore a bit like an autodyne & has to use a tapped Hartley oscillator, or the recommended external exciter. I have serviced a Midwest autodyne where the exciter was a Colpitts. One may have to fiddle with voltages & signal levels to get a useable modulation & toy with an extra amp. Application to it of AGC may be an issue.

With a non tube test & play oscillator, the oscillator was 3/4 of a quad NAND gate (into a delay chain to get a modified square wave. The mixer was a dual gate FET. RF into one gate, Audio via pot, into the other to control modulation for a demo, where needed.

Marc

Thanks Marc all taken on board, i'm onto a coin project at the moment (the varieties of the 1952 dated Perth Mint pennies) and will swing back to the radio when I get that out of my system. I was even doubtful if the tapped coil set up would actually work and was amazed when it fired up with my plain guess work coil turns. More work to do with the 6BE6 however.

Interesting tube the 6SA7 and on a different subject I found it worked so well as a convertor but even more so when using it as a discriminator in my syncrodyne experiments. It was a very "smooth" valve to use if I can use a very non tech term!

Fred.

Americans seem to have issues with it, it can be a swine to get oscillating, which is probably why the valve manufacturers say "external exciter". It appear to have similar features to a Pentagrid like 6A8, so an oscillator formed with grid one similar to 6A8, I would see as workable.

The problem of course is balancing the level of signal as mentioned, to sustain a decent modulation. As we know (and it is written by the prophets who make them) as the frequency increases with 6A8 and others (Not 6SA7) AGC serves to destabilise. That is why AGC is commonly discontinue on a SW band. However, if there is a TRF stage first, AGC can be applied to it, to help modulation.

All entertaining.

Marc

This little build is the Vintage Radio article in the June 2025 issue of Silicon Chip page 94.
They have compacted the 3-part series into 7 pages and maintained the gist of the story.
The receiver is in contrast to the SSB receiver article by Charles Kosina on page 46!!
Fifty years of technology has made quite a lot of advances but the basic bones of a Superhet is the same.
My little set is a good '101' tutorial on how to make a Superhet from scratch of the 1970 era.
Thanks to Silicon Chip for the attention paid to the story and the article presentation.

Fred.

It has been a few years since I've subscribed to SC but I will try and grab a copy from a newsagent and check the article out.

Yea Brad grab a copy.

I'm subscribing and read the magazine as a way of keeping up with electronics and technology in many different fields.
Of particular interest over the last couple of years are things like the explanations of our power generation/distribution systems, farming and ag, and how the internet works mainly by undersea cable. Articles are written by people who research and seem to know a bit about the subjects. These clarify and refute the complete rubbish propagated by vested interest or politicians.
I would be the least qualified contributor but still get a spot now and then.

It's the closest thing we have to a 'Scientific Australian'!
Fred.

The various ways that earth can be implimented on AC systems was also very informative.

There was a Scientific Australian way back in the eighties or so, but unfortunately did not last long.

Yes I agree with Fred.
I just read your article Fred. They did it justice, I think, well done!
I might submit my CRT tester for publication.
It had another win yesterday, read about it in the post,