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 Point to Point wiring
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 Return to top of page · Post #: 1 · Written at 4:12:06 PM on 3 September 2020.
Destino's Gravatar
 Location: Bells Beach, VIC
 Member since 20 July 2020
 Member #: 2428
 Postcount: 39

Hi there folks.

I'm quite new to this game. However I'm trying to trace the circuit of a Calstan 529 5 valve radio. Some of you have been very helpful to date with explaining a few things for me.

I've been trying to trace the circuit out and match what I have in the chassis with what is on the circuit diagram that I have.

Is it my imagination, inexperience or naivety. Some of the wiring seems to go through convoluted hoops to get where it needs to go.

If I were to get several "identical factory fresh" radios would they be exactly the same. I know they would ultimately be electrically identical but did they care. Did it depend on what assembly folks made a particular radio.

Do we know if one person made the entire radio or were there assembly lines as we know them.

What was the trouble shooting department at the end like? Was there a whole pile of "dead" radios on a bench that some poor tech had to work through?

In the radio I have they appear to be particularly fond of non connected valve pins as terminal spots.

Cheers and Thanks


 Return to top of page · Post #: 2 · Written at 6:22:48 PM on 3 September 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2109

Re point to point wiring:

Except for very small concerns, all radios of the same model were generally built the same way. It would be very unwise to make them different, especially as the semi-skilled workers really had no idea of what they were wiring, samples and diagrams were copied slavishly. Having said that, small changes were sometimes made in production due to component sourcing or production yield issues.

Generally, there were several "stations" building a chassis. It was divided up into stages like component mounting, bus wiring (e.g. heaters), a couple of component fitting stations, followed by alignment and final test. Yes, the tricky ones were put aside for more expert attention. Usually there would be a progress card, initialled by each operator so if problems were found it would be known who did it.

A smaller organisation like KGH (Calstan) might telescope the number of stations but it was rare for one operator to do everything.

Using unused valve pins as tie points in radios with octal or even B9A sockets was common. Normally, pins listed as "n/c" (no connection) were used. "i/c" (internal connection) pins were avoided. Later, in TVs where all pins were connected, this was not possible.

 Return to top of page · Post #: 3 · Written at 9:10:33 PM on 3 September 2020.
Robbbert's avatar
 Location: Hill Top, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1737

Using n/c pins on octal output valves was very common.

From what I've heard, the path of the wiring was determined by the engineer, in order to avoid unwanted feedback or radiation pickup that might result from another route. So, the original route should be followed unless it's giving trouble.

I had one radio where a long wire was picking up mush from the output stage but fortunately it was by the front metal panel and there were convenient holes to allow the wire to run on the other side. This completely fixed the problem.

 Return to top of page · Post #: 4 · Written at 9:57:54 AM on 4 September 2020.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 453

Hi Peter,

I have gone "nuts" trying to trace out radio circuit diagrams ... my wife says that she cannot tell the difference .... Smile

The approach will depend, obviously, if the radio has been worked on by some-one else, how many stages it has, whether you are wanting to learn how it works, or just want to get it going. I like to learn how each radio works, how each stage works, interacts etc ...

So I my first 'pass' is focused on each valve ... what is its purpose, what is each pin, what should be connected to each pin versus what is connected to each pin. For example .... start with Mains input and Rectifier, then RF, Mixer, IF(s) etc ... initially, I only trace wires within each stage ... Then take a step back and trace all Heater wiring, DC to each stage, then trace Signal through radio (AC path).

As to point-to-point wiring ... I have a couple of pieces of Quad gear (British manufacturer, not quadrophonic) ... high-end gear ... they do not use point-to-point wiring .... all perfectly routed around edges of chassis etc ... one could argue that this provides better shielding, but just as easily, one could argue that wires must be longer leading to losses, inductance etc.. ... depends on a lot of factors ... but sure makes tracing out a circuit much easier ... Smile

Cheers, Ian

 Return to top of page · Post #: 5 · Written at 10:15:35 AM on 4 September 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4749

With radios most of the old ones followed a similar plot. Coloured markers are helpful. Blue for screens, red Plates green heaters & filaments, black cathodes; if there is no colour code. You even add dots to switches and wires of the same colour, or to separate switch banks.

I start by drawing (AutoCAD) the chassis layout, IFs & cans with pins coils and transformers with its wiring layout and valves with elements for clarity. Then you play join the dots. That gives you a layout diagram. Colour is useful there as well.

Do take photos. I do not care if its wrong, right, or tampered with, at this point. After you get the circuit, "as is", from the layout, you go sort the obvious errors: Not before.

 Return to top of page · Post #: 6 · Written at 10:43:44 AM on 4 September 2020.
Destino's Gravatar
 Location: Bells Beach, VIC
 Member since 20 July 2020
 Member #: 2428
 Postcount: 39

Hi there.

Thanks for your comments.

Seems I'm not alone in going a little crazy.

I've pretty much been doing what has been suggested. However I didn't quite expect it to be so convoluted. Considering there are not that many parts.

It was the use of the unused pins that threw me at at first.

I want to get it working again but in the process I want to understand how it works.

I've replaced each of the paper and electrolytic capacitors one by one so it should still be as it was originally constructed. I still have some work to do.

Its the various coils down one end that are the focus of my attention at the moment.

Once again many thanks.


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