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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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28th Feb 2021, 11:13 am | #1 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
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Capacitor voltage?
For use in a tight space in a Pye M78F that I'm restoring (see other thread in wireless section) I want to use this 0.01uF cap (marked '103' = 10,000pF = 0.01uF)). The problem is, it doesn't show a voltage rating. Does anyone know what it's voltage rating is, or is likely to be? Its position in the circuit is C7, HT feed decoupling. See circuit diagram. My HT into the set will be 74V. But that is dropped via R12 ((680ohms) and R2 (10K) to get to C7. Trader valve voltage table also shown - bear in mind the voltages quoted are based on the HT being 67.5V.
Is this cap suitable? Otherwise it's not the end of the world, I'm pretty sure I may be able to find a cap that I can shoe horn into the very limited space but the cap I'm talking about would be ideal size wise. The set was build layer by layer, and there's a number of short wires etc lying over the cap in question that will be a pain to unhook or even replace. It's all very tight, like performing open heart surgery on a mouse. Originally the cap would have been fitted first, then those obstructive wires.
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28th Feb 2021, 12:28 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,528
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Re: Capacitor voltage?
Looks like a multilayer ceramic job. Probably 50V though could be 100V but with no ID who knows?
It would probably be OK, failure would be a nuisance, not a disaster but with something like these available: https://www.ebay.co.uk/itm/0-01uF-10...edirect=mobile why risk it?
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28th Feb 2021, 12:47 pm | #3 | |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
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Re: Capacitor voltage?
Quote:
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28th Feb 2021, 1:06 pm | #4 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
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Re: Capacitor voltage?
That size cap is 50V and probably borderline for what you want.
I would go with the 100V ones. |
28th Feb 2021, 1:26 pm | #5 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: Capacitor voltage?
If the blue cap is 50 volts working, then it should be fine.
From the voltage table the bottom of R2 has 33 volts on it (V2 screen) so add 5 volts for safety (higher HT and digital meter) and you are still less than 40 volts. It will only 'see' more for the fraction of a second before the valves start to conduct at switch on... You could try putting one in series with a 10kΩ resistor across your 74 volt HT and see what happens?
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28th Feb 2021, 1:29 pm | #6 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
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Re: Capacitor voltage?
Those radial ceramic packages are prone to have their legs tear off at the slightest stress.
David
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28th Feb 2021, 5:09 pm | #7 | |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
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Re: Capacitor voltage?
Quote:
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1st Mar 2021, 10:41 am | #8 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: Capacitor voltage?
All good then...
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2nd Mar 2021, 11:06 am | #9 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,809
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Re: Capacitor voltage?
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A digital radio is the latest thing, but a vintage wireless is forever.. |
2nd Mar 2021, 1:49 pm | #10 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Capacitor voltage?
These were used as TTL rail (5V) decoupling capacitors.
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