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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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12th Mar 2019, 2:30 pm | #1 |
Retired Dormant Member
Join Date: Dec 2015
Location: Chipping Norton, Oxfordshire, UK.
Posts: 11
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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 |
12th Mar 2019, 2:57 pm | #2 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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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. |
12th Mar 2019, 7:59 pm | #3 |
Retired Dormant Member
Join Date: Dec 2015
Location: Chipping Norton, Oxfordshire, UK.
Posts: 11
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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 |
12th Mar 2019, 9:15 pm | #4 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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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. |
12th Mar 2019, 11:30 pm | #5 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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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. |
13th Mar 2019, 12:10 am | #6 |
Heptode
Join Date: May 2008
Location: Selby, North Yorkshire, UK.
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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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13th Mar 2019, 12:07 pm | #7 |
Dekatron
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Re: PCB diode markings Pye Labgear
Yep, the + on the PCB indicates the end the +volts come out of
Lucien's memory hasn't let him down either.
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13th Mar 2019, 10:31 pm | #8 |
Retired Dormant Member
Join Date: Dec 2015
Location: Chipping Norton, Oxfordshire, UK.
Posts: 11
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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 |