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Clubs, Groups and Societies For discussions about various clubs, groups and societies relating to our hobbies, such as the BVWS (incl RetroTechUK), BATC, RSGB, APTS, CLPGS, THG, TCC, BECG, MCR21 etc. This is NOT an official forum for any of these organisations.

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Old 17th Feb 2018, 6:00 pm   #1
60 oldjohn
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Default BVWS Capacitors

Most know the BVWS sell the yellow 630v metallised polyester film capacitors to BVWS members at events around the country. But do or will they stock 1000v rated ones for tone correction use?


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Old 17th Feb 2018, 8:24 pm   #2
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Default Re: BVWS Capacitors

Not that I have ever seen.
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Old 17th Feb 2018, 9:09 pm   #3
M0FYA Andy
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Default Re: BVWS Capacitors

Why does 'tone correction' require 1000v capacitors?

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Old 17th Feb 2018, 9:14 pm   #4
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Default Re: BVWS Capacitors

I think Andy,because folks have stated that is what is needed across sound tx,s.Spikes I guess.
I have I admit used less rated before without problems.
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Old 17th Feb 2018, 9:53 pm   #5
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Default Re: BVWS Capacitors

Quote:
Originally Posted by M0FYA Andy View Post
Why does 'tone correction' require 1000v capacitors?
Because unusually high voltages can appear across the primary of the audio output transformer.
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Old 17th Feb 2018, 10:35 pm   #6
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Default Re: BVWS Capacitors

OK, I hadn't thought about directly across the output transformer, I was thinking about filter components in tone control circuits, so low-level signals.
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Old 17th Feb 2018, 11:07 pm   #7
60 oldjohn
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Default Re: BVWS Capacitors

I have a Pye PE80 on the bench at the moment Tone correction caps are shown as 300v AC which I think would equate to around 900v DC, hence the 1000v DC needed. I would guess that it would be same for most valve sets.


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Old 17th Feb 2018, 11:12 pm   #8
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Default Re: BVWS Capacitors

In many cases, perhaps most cases, the capacitor across the output transformer of a normal commercial radio will be found as an old waxy rated at 500v DC.

Dependant on the manufacturer and the range being used (hunts black/brown, Metalpack, Sprague etc.) the voltage rating on the cap will be the most appropriate in the specific range.

You must remember manufacturers did deals with component suppliers to get the keenest price for the required component and even changed the design in some way to fit in with getting this best price break for quantity purchases.

The BVWS range was specifically chosen at 630v DC so as to be as useful as possible to restorers. They don't have to be 630v and in fact the 400v range would probably sufficed for most things.

There are no plans for the BVWS to stock 1kv rated caps.

Mike...
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Old 17th Feb 2018, 11:25 pm   #9
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Default Re: BVWS Capacitors

Thank you Mike.


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Old 18th Feb 2018, 9:43 am   #10
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Default Re: BVWS Capacitors

Often seen 1000 volt ceramics used with that type of tone control.
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Old 18th Feb 2018, 12:14 pm   #11
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Default Re: BVWS Capacitors

Stick two in series if you're that worried. A short circuit failure across the primary won't hurt anything anyway. Beware of anode-chassis connected ones, though!
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Old 20th Feb 2018, 2:24 am   #12
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Default Re: BVWS Capacitors

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Stick two in series if you're that worried.
That's exactly what I do. Just double the capacitance value of each to give you the same original value.
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