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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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14th Mar 2023, 11:38 pm | #21 |
Dekatron
Join Date: Nov 2009
Location: Lincolnshire, UK.
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Re: PYE Blackbox four speaker
Having worked on these, the only capacitors that you'll really need to replace are the four paper types C6,7,9,10. You might want to also replace C11, which is the output stage cathode decoupler and is the Plessey one that you mention. I haven't actually found any problem with this type myself in record players in general, including the Pye BB, but they are known to be very unreliable in other applications where they're probably more stressed, such as in older TVs. Always replace with nearest preferred modern equivalent value, at or a little above the stated working voltage, but never below.
You won't need to replace any other capacitors unless you have mains hum, or the main smoothing can starts to get warm after a short time - keep checking it and it would be a prudent idea to give it a bit of a chance to do a bit of reforming by using a lamp limiter, but only after you've replaced particularly C9 & 10. You can go round all the resistors with your meter to check for any that are significantly out of tolerance - you may find the cathode resistor, R25 (that's the one connected across that Plessey capacitor) has risen in value, perhaps just a little, but possibly by a lot. One thing for certain is that it doesn't want to be in close contact with that capacitor, as they always seem to have been when fitted by Pye - very bad practice, but they're all like that. |
14th Mar 2023, 11:49 pm | #22 |
Dekatron
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Re: PYE Blackbox four speaker
I'll make this another post rather than edit the last one in case you miss it, as I've left out the most important thing to check before going any further, and that is to check the continuity of all of the primary winding of the output transformer, as these are a known weakness if someone has previously run it with leaking capacitors C9 & C10. If one half of the winding is open circuit, as it sometimes is, then it'll need a professional rewind.
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14th Mar 2023, 11:53 pm | #23 |
Hexode
Join Date: Aug 2014
Location: Wigston, Leicester, UK.
Posts: 351
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Re: PYE Blackbox four speaker
Hi, just Google 'ecc82 datasheet'
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15th Mar 2023, 12:02 am | #24 |
Dekatron
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Re: PYE Blackbox four speaker
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15th Mar 2023, 3:27 am | #25 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
I will check the primary windings for continuity. Thanks for the great advice.
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15th Mar 2023, 3:33 am | #26 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
In the valve split diagram on the schematics, I found it hard to understand the valve pin order in the direction (forgot it was clockwise or anti clockwise 1, 2, 3....) and identify each viewed from the lower part of the chassis. I am trying to identify the valve pins which is which like on each of V1A and V1B -1/2 ECC82, V2A and V2B-1/2 PCL83, V3A and V3B-1/2 PCL83. Once I know that I can follow the pins and identify the paper caps and its value. I also like to know the voltages on those valve pin numbers.
Last edited by RoyceVM; 15th Mar 2023 at 3:56 am. |
15th Mar 2023, 3:35 am | #27 | |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
Quote:
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15th Mar 2023, 1:22 pm | #28 |
Dekatron
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Re: PYE Blackbox four speaker
Doesn't that under-chassis wiring look terrible in Post #15! The Girls cussed about these. Not only are the components so close together horizontally, they were stacked on top of each other. There was plently of room within the cabinet for a much larger chassis.
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Edward. |
15th Mar 2023, 2:57 pm | #29 | |
Hexode
Join Date: Aug 2014
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Re: PYE Blackbox four speaker
Quote:
Royce, remember that the pins are numbered clockwise as you view them from underneath, starting at the gap. |
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15th Mar 2023, 3:33 pm | #30 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
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15th Mar 2023, 3:39 pm | #31 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
Some additional pics of the transformer area
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15th Mar 2023, 3:41 pm | #32 | ||
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
Posts: 91
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Re: PYE Blackbox four speaker
Quote:
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15th Mar 2023, 4:03 pm | #33 |
Dekatron
Join Date: Nov 2009
Location: Lincolnshire, UK.
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Re: PYE Blackbox four speaker
If you look at your circuit diagram that you posted you will see that there should be 5 connections to the primary. I think the readings that you've posted so far are ok, but the important one is to take a reading between the two ends of the winding, ie, where the anode of V2B and R27 connect to one end and the anode of V3B and R28 connect to the other end - you should be able to identify these from the circuit and what you have in front of you on the amplifier chassis.
The secondary will have a very low resistance of an ohm or so, which you have measured as just continuity. |
15th Mar 2023, 4:26 pm | #34 |
Dekatron
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Re: PYE Blackbox four speaker
You may have already measured the end to end readings without realising it and it's the one quoted above as 189 ohms. If it is, then this is probably correct and the transformer is fine, but just verify that this is definitely the case from my instructions in the previous post.
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15th Mar 2023, 4:32 pm | #35 | |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
Quote:
There is no center tap. Pin 1 went to V3B and R28 and Pin 4 went to V2B and R27. |
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15th Mar 2023, 4:40 pm | #36 |
Dekatron
Join Date: Nov 2009
Location: Lincolnshire, UK.
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Re: PYE Blackbox four speaker
Yes, you've got it - see my previous post #34.
Last edited by Techman; 15th Mar 2023 at 4:41 pm. Reason: Corrected stated post number. |
15th Mar 2023, 5:17 pm | #37 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
Now I have to change all that old paper capacitors. I need to identify it one by one, then order them and replace it with film capacitors.
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15th Mar 2023, 5:37 pm | #38 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
Got the ECC82 diagram
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15th Mar 2023, 5:38 pm | #39 |
Dekatron
Join Date: Nov 2009
Location: Lincolnshire, UK.
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Re: PYE Blackbox four speaker
Well there's only the 4 that I showed you plus that Plessey electrolytic and it's job done!
There's others that you might want to replace, it's up to you, but you risk creating other faults as it's a bit of a rats nest in there. Replacing other components that don't really need replacing won't make the amplifier work any better and may even lead to the instability that these amplifiers are known for. |
15th Mar 2023, 5:40 pm | #40 |
Tetrode
Join Date: Mar 2023
Location: Niles, Illinois, USA.
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Re: PYE Blackbox four speaker
Thanks again for your help!
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