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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 12th Mar 2019, 2:30 pm   #1
Nungesser
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Default PCB diode markings Pye Labgear

Hello,
I have a Pye compak 8 military transceiver that requires a few component changes following an overheat event.
I am confused by the diode markings on the pcb.
All of the many diodes fitted have their stripe (-ve) end facing a + mark on the board.
Is this + mark not a positive but a cross or x denoting where to place the -ve lead?

Also this question still stands for the polarised tantalum bead capacitors that are on the boards. I.E is the + or x a negative lead location?

I have also seen pictures on the web showing an internal view of a Pye Cambridge telephone PCB and all the shown diodes have the stripe to + or X mark.

Any advice is welcome as I need to know the markings before I replace some unidentifiable ,untestable, overheated components.

Kind Regards

David
2E0EYR
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Old 12th Mar 2019, 2:57 pm   #2
ms660
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Default Re: PCB diode markings Pye labgear

The stripe/band on the diode is the cathode, a + or - sign on a capacitor indicates that it is of the polarised type, the correct polarity should be observed when replacing.

Lawrence.
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Old 12th Mar 2019, 7:59 pm   #3
Nungesser
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Default Re: PCB diode markings Pye Labgear

Hi Lawrence,

Thank you for a fast reply.

I do realise and know what you said.
My question is about the markings on the vintage printed circuit board.

On both my Pye transceiver and the Cambridge telephone mentioned have the negative cathode facing what looks like a + or x printed on the board.

Kind Regards
David
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Old 12th Mar 2019, 9:15 pm   #4
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Default Re: PCB diode markings Pye Labgear

The way I would look at it is that an output voltage from the diodes cathode will be positive and if it was a Zenner diode the input to the cathode would be positive.

Lawrence.
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Old 12th Mar 2019, 11:30 pm   #5
Lucien Nunes
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Default Re: PCB diode markings Pye Labgear

Before the stripe became universal, wasn't the cathode of a diode conventionally marked (+) ? TBH it's so long since I've consciously thought about it, that I couldn't say what I would expect to see. But I think that had I been given a PCB with two holes, one marked (+), and a diode, I would automatically have installed the diode with cathode to (+).

The cathode is the terminal from which conventional current flows out, or electrons flow in, hence a positive cathode implies a source of energy, while a negative one implies a load. Since a rectifier diode is not conventionally a load intended to consume energy, there is some logic in assuming it to be a source and denoting its cathode (+). Perhaps there is a simpler explanation.
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Old 13th Mar 2019, 12:10 am   #6
Martin G7MRV
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Default Re: PCB diode markings Pye Labgear

Have you got the service manual?

Its available here http://www.royalsignals.org.uk/uk-co...lth-rx-tx.html
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Old 13th Mar 2019, 12:07 pm   #7
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Default Re: PCB diode markings Pye Labgear

Yep, the + on the PCB indicates the end the +volts come out of

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Old 13th Mar 2019, 10:31 pm   #8
Nungesser
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Default Re: PCB diode markings Pye Labgear

Hello All,
Thank you for your advice.
I have the manual now.
Its still not too clear but I can work it out.

I searched practical wireless and practical television articles from the same era (1970s) and found the following quotes.

1. In P Wireless:- "Note that the end of the diodes marked positive in Fig. 25 corresponds to the cathode, and to a black or
coloured band on the component itself. "

In the figure 25 the pcb had + marks where the striped diodes were fitted.

2. in P television :-"all diode markings indicate a cathode connection"

It does seem that in the early 70s pcb markings were a + for the cathode.

the investigation will continue but with a wiring diagram I will be able to work it out.

Kind Regards

David
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