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Old 2nd May 2019, 9:38 pm   #1
Northyorks1
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Default Bush VHF70 Capacitor identification.

Hello,

Can anyone tell me which capacitor is the mains filter cap in the bush vhf70, as I want to replace it for an X class . I can't seem to pinpoint it in the trader sheet.

Thanks Ian.
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Old 2nd May 2019, 9:46 pm   #2
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Default Re: Bush vhf70 Capacitor identification.

You'll be looking for C65 which is connected in series with the scale lamps and their shunt resistor across the switched mains.

Lawrence.
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Old 2nd May 2019, 9:49 pm   #3
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Default Re: Bush vhf70 Capacitor identification.

Ian,

C65

Andrew

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Old 2nd May 2019, 10:14 pm   #4
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Default Re: Bush vhf70 Capacitor identification.

Thanks very much Lawrence and Andrew. Is that the 500 volt electrolytic?
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Old 2nd May 2019, 10:36 pm   #5
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Default Re: Bush vhf70 Capacitor identification.

Hi.

The mains filter cap is 0.05uF 250Vac. The circuit reference as mentioned by Lawrence and Andrew is indeed C65 for the "Trader" service sheet.
If using the manufacturer's service information, the circuit reference is C60.

A suitable replacement would be a 0.047uF Class X2 which will be rated for connection across the mains.

Regards,
Symon

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Old 2nd May 2019, 10:38 pm   #6
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Default Re: Bush vhf70 Capacitor identification.

A mains filter capacitor is never going to be a 500V electrolytic, that will be a smoothing capacitor.

The mains filter capacitor is C65, 0.05uF and probably a waxie.
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Old 2nd May 2019, 10:58 pm   #7
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Default Re: Bush vhf70 Capacitor identification.

That is why I questioned about the electrolytic capacitor, as on Trader service sheet 1419 it shows cap 65 as the electrolytic cap, thats if I am reading it properly.

Thanks again for help

Ian
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Old 2nd May 2019, 11:05 pm   #8
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Default Re: Bush vhf70 Capacitor identification.

Electrolytic capacitors are shown on that service sheet with +ve and -ve symbols to indicate polarity. C65 doesn't have polarity markings so it isn't an electrolytic.

In any case 0.05uF is too small a value of capacitance to be an electrolytic. They generally start at around 1uF.

The chassis layout diagram shows exactly where C65 is located.
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Old 2nd May 2019, 11:10 pm   #9
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Default Re: Bush vhf70 Capacitor identification.

Hi Ian,

You're not reading it properly

You've got two electrolytics in a big silver can, one of those is circled in red in my snippet, with polarity marked +/- and C65 which is a not an electrolytic. I'm generalising but at this vintage anything over 1uF in value is likely an electolytic, anything under is not.

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Old 2nd May 2019, 11:11 pm   #10
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Default Re: Bush vhf70 Capacitor identification.

On my Trader Sheet 1419 C65 is shown as an ordinary capacitor (as per the snip in #3). It could never be an electrolytic in that position.
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Old 3rd May 2019, 12:24 am   #11
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Default Re: Bush vhf70 Capacitor identification.

My mistake and lack of knowledge. I have added a pic of what I assume is cap 65.

Ian.
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Old 3rd May 2019, 8:15 am   #12
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Default Re: Bush vhf70 Capacitor identification.

I'd check that carefully against the component layout but I would not have expected a 350V DC capacitor to have been fitted in that position. More likely 750V or 1000V DC (1000V DC rating is about the same as 300V AC rating)
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Old 3rd May 2019, 8:23 am   #13
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Default Re: Bush vhf70 Capacitor identification.

The cap has at least two ratings on the can, the 350v DC is at 100C, it looks like there is another rating at 70C but I cannot read it.

Yes needs careful checking.
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Old 3rd May 2019, 8:34 am   #14
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Default Re: Bush vhf70 Capacitor identification.

Per the Bush service sheet the spec was 0.05uF at 500V. Not all capacitors in metal cans are electrolytics, I think that could be where you're getting muddled?

Just wondering, before any components get swapped out, what the working state of the set is?

Andrew
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Old 3rd May 2019, 8:35 am   #15
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Default Re: Bush vhf70 Capacitor identification.

Hmm yes...….it could be 500V DC at 70C but still pushing things if it's across the mains.....! If that is C65, you need to replace it with an X cap. These are rated and designed to be connected across the mains. It won't hurt to temporarily disconnect it altogether while you are testing the set.
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Old 3rd May 2019, 8:47 am   #16
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Default Re: Bush vhf70 Capacitor identification.

C65 (Trader sheet) is on the rear of the voltage change panel.
It is that metal canned cap, I suspect that it is not the original cap as everyone I have seen before in a Bush is a waxy.
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Old 3rd May 2019, 8:51 am   #17
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Default Re: Bush vhf70 Capacitor identification.

500V DC cap rating (peak) x 0.707 (rms) = 353V AC rating. Mains 240V (rms) x 1.414 (peak) = 339V....call it 340V.....that's pretty close to the maximum AC rating of the cap taking into account surges and spikes and other rubbish that appears on the mains. Mind you....it's lasted all these years...…!
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Old 3rd May 2019, 9:10 am   #18
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Default Re: Bush vhf70 Capacitor identification.

Cost engineering. No point in overspecifying a part in a consumer item even in the 1950s. No legislation requiring a special part then, either.

Good for ten years or so and even if it goes BANG the fallout would likely not escape from the cabinet and might prompt the purchase of a new radio
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Old 3rd May 2019, 11:33 am   #19
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Default Re: Bush VHF70 Capacitor identification.

Hello everyone,

Due to my limited knowledge I did not know that it was not an electrolytic capacitor, just saw a metal can and assumed so. And then got a bit confused looking for a waxy. I have taken in the previous comments regarding electrolytic caps, thanks. Radio has not been powered up, but I was told that it is in working condition. Thank you for your replys and patience.

Ian

Data on cap
0.05uf + - 20%
500v DC 70C
350v DC 100C
TYPE CP 45S
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Old 3rd May 2019, 11:37 am   #20
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Default Re: Bush VHF70 Capacitor identification.

Just snip it out for the time being. The set will work perfectly well without it.

Replace C61 (Trader sheet) the audio coupling capacitor before you connect the set to the mains and switch it on. You don't want to destroy the output transformer which has a tapped primary winding.
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