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Old 20th Feb 2018, 5:24 pm   #21
ukcol
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Default Re: Mullard MAS1764

To expand on what Bill said in post 2 and what dazzlevision has just said. The audio amplifier in the Philips 643A is quite a lot more complicated than your average set. Instead of "that" capacitor" (one component) there are no less than 4 capacitors (C59, C60, C62 and C63) that could cause damage if leaky.

See snip below.

The munufacturer's manual is available here.

https://www.service-data.com/section.php/5896/1/643a
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Old 1st Mar 2018, 1:21 am   #22
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Default Re: Mullard MAS1764

Belatedly many thanks for that - I was struggling. I have the "Trader" Service sheet 1208. https://www.************************...ILIPS/543A.PDF

and I will certainly get those you list.

I fear I am still a little confused. Are those Cap numbers (59, 60, 62 & 63) on your 'snip' taken from the manufacturers circuit diagram - unless I'm being particularly obtuse (a distinct possibility) they don't seem to tally with my 'Trader' service sheet numbers where C59, for example, is only one of a set of four Neg feed-back tone correctors (1500pF).
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Old 1st Mar 2018, 1:32 am   #23
ukcol
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Default Re: Mullard MAS1764

Quote:
Originally Posted by petergamston View Post
Are those Cap numbers (59, 60, 62 & 63) on your 'snip' taken from the manufacturers circuit diagram...............
Yes Peter, the snip is from the manufacturer's service data and not the Trader sheet.

The manufacturer's data is available here:

https://www.service-data.com/product...05/5896/m14605
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Old 1st Mar 2018, 3:10 am   #24
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Default Re: Mullard MAS1764

Trader sheets rarely agree with the component numbers on other sheets as they reverse engineered their own off an actual set.
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Old 2nd Mar 2018, 6:29 pm   #25
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Default Re: Mullard MAS1764

I might be missing something, but the R34/35 network on the shown circuit seems rather odd. Is it the same on the other diagrams? Tony.
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Old 2nd Mar 2018, 7:36 pm   #26
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Default Re: Mullard MAS1764

So far as I can make out it's drawn correctly, either side of center is treble cut by equal amounts but only on side of center gives treble cut and bass boost, the bass boost switches are ganged to the tone control. There's a brief description in the Trader for the 543a which shows a similar circuit although there appears to be a discrepancy with S25, S26 in the description....So far as I can make out.

Lawrence.
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