PYE Blackbox four speaker

[RoyceVM]

I believe I identified C13 and C 14 and both were connected to one pin on the primary of the output transformer.
They both read 40nF. It should be 0.004uF.
I had those in my collection of yellow film caps from Just Radios reading 472K/630V which is 0.0047uF

Top left, Top middle and top right was used to refer when you view the back side of the chassis with the transformer side down resting like that and the two controls pointing upward.

Pin #9 on top left ECC82 was connected to a paper cap and it read 135nF. It should be 0.04uF.

Pin #9 of the top middle ECC 82 was connected to a paper cap and it read 100nF. It should be 0.04uF. Pin #2 of the same ECC82 was connected to a paper cap that read again 100nF which should be 0.04uF.

Pin #9 of PCL 83 was connected to a paper cap that read 135nF which should me 0.04uF.
The above 4 caps should be C6, C7, C9, C10 but I was lost identifying them. Pardon me!

I have yellow film caps from just radios 473K/630V which is 0.047uF for replacing those 0.04uF caps (4).

For the C11 25uF/25V can I replace it with 50uF/630V? If so, I have that electrolytic cap in my stock.

[RoyceVM]

Some pics and reference tables

[Techman]

An important fact to note is that you can't use a capacitor tester to test old capacitors, as it'll always give stupid readings that are always higher than they should be, so don't bother with it.

If you want to replace C13 & 14, then these need to be modern 400-630 volt types.

C11 - no, you can't use a 50uf/630 volt type...that would be absolutely massive, so I think you've made some sort of a mistake with that one! Look for something around 22uf/25-50 volts.

All the other paper capacitors other than the four that I mentioned previously will make absolutely no difference to the operation of the amplifier whether they're replaced or not. That's not saying that they're not slightly leaky, they will be, but it's about understanding the circuit and how any leakage that they may or may not have will affect it. I would go with replacing C13 & 14 if you really want to, but they're not particularly critical if they failed, even where they're situated on the transformer, they've got a 3.9K resistor in series with them anyway.

To help show you where the four critical paper capacitors are, C6,7,9,10, I've posted below, three pictures of one of these amplifiers that I repaired four years ago and I can tell you that it's been in regular use since then and it sounds absolutely amazing, with deep thumping bass and crystal clear mid range and treble...and it's just had those four capacitors replaced and I seem to remember one resistor, but I can't remember which one. The Plessey capacitor is still in place and working fine, just being prised away from the 220 ohm resistor that it's in parallel with, as it's not a good idea to have them hard up against each other as Pye originally wired them. To be fair, the Plessey capacitor ought to be replaced, but four years on has proved that it wasn't faulty then and it's still not faulty now.

Regardless of the Pye data showing these capacitors as 0.04uf/150 volts, they should be replaced with 0.047uf/400-630 volt types, although any voltage of 250 volts or above will be fine...those capacitors in the final picture are actually 0.1uf, used because I'd run out of 0.047uf types at the time and the amplifier performs perfectly fine, probably better with these.

Below, the first picture is the top of the chassis view to confirm it's the same model as yours. The second picture shows the chassis with the original capacitors before replacement, and the last picture shows C6,7,9 & 10 only replaced, and then it was put back together and it's still working fine today. So to sum up, replace the four capacitors mentioned and the Plessey one, plus the two C13 & 14 won't do any harm. Check all the resistors and replace any that are wildly out of tolerance, particularly that 220 ohm cathode resistor, which will probably be slightly high, but so long as it's not too far out it'll not make any difference to the sound, but will give the valves and the transformer a slightly easier time.

[RoyceVM]

Originally Posted by RoyceVM

Some pics and reference tables

Just wanted to add the amp pic for reference.

[RoyceVM]

Originally Posted by Techman

An important fact to note is that you can't use a capacitor tester to test old capacitors, as it'll always give stupid readings that are always higher than they should be, so don't bother with it.

If you want to replace C13 & 14, then these need to be modern 400-630 volt types.

C11 - no, you can't use a 50uf/630 volt type...that would be absolutely massive, so I think you've made some sort of a mistake with that one! Look for something around 22uf/25-50 volts.

All the other paper capacitors other than the four that I mentioned previously will make absolutely no difference to the operation of the amplifier whether they're replaced or not. That's not saying that they're not slightly leaky, they will be, but it's about understanding the circuit and how any leakage that they may or may not have will affect it. I would go with replacing C13 & 14 if you really want to, but they're not particularly critical if they failed, even where they're situated on the transformer, they've got a 3.9K resistor in series with them anyway.

To help show you where the four critical paper capacitors are, C6,7,9,10, I've posted below, three pictures of one of these amplifiers that I repaired four years ago and I can tell you that it's been in regular use since then and it sounds absolutely amazing, with deep thumping bass and crystal clear mid range and treble...and it's just had those four capacitors replaced and I seem to remember one resistor, but I can't remember which one. The Plessey capacitor is still in place and working fine, just being prised away from the 220 ohm resistor that it's in parallel with, as it's not a good idea to have them hard up against each other as Pye originally wired them. To be fair, the Plessey capacitor ought to be replaced, but four years on has proved that it wasn't faulty then and it's still not faulty now.

Regardless of the Pye data showing these capacitors as 0.04uf/150 volts, they should be replaced with 0.047uf/400-630 volt types, although any voltage of 250 volts or above will be fine...those capacitors in the final picture are actually 0.1uf, used because I'd run out of 0.047uf types at the time and the amplifier performs perfectly fine, probably better with these.

Below, the first picture is the top of the chassis view to confirm it's the same model as yours. The second picture shows the chassis with the original capacitors before replacement, and the last picture shows C6,7,9 & 10 only replaced, and then it was put back together and it's still working fine today. So to sum up, replace the four capacitors mentioned and the Plessey one, plus the two C13 & 14 won't do any harm. Check all the resistors and replace any that are wildly out of tolerance, particularly that 220 ohm cathode resistor, which will probably be slightly high, but so long as it's not too far out it'll not make any difference to the sound, but will give the valves and the transformer a slightly easier time.

Thanks so much! I will use 25uF/25-50V for C11. Is there a problem with the voltage higher than 50V because all the sellers give higher voltage caps. Thanks for the reference pic. That will help me a lot!

[Techman]

Originally Posted by RoyceVM

Is there a problem with the voltage higher than 50V because all the sellers give higher voltage caps.

Yes, it's not good practice to go too far over the top with the working voltage of an electrolytic capacitor. Most sellers will stock 63 volt working types as the modern preferred value for this application and you should go no higher than that. A quick look on-line shows both 22uf and 33uf electrolytic capacitors readily available at 63 volts working, but if you can get the exact 25uf value at around that working voltage, then that would be perfect. Make sure you get 'axial' types rather than the radial types.

Note that one of the 0.04uf brown Hunts capacitors that you need to replace is in an awkward position tucked away behind some resistors. Snip this capacitor out and once removed fit the replacement as I've done - it's the yellow one shown vertically on the right hand side of my 3rd picture in the previous post. You can't quite see the original one in my 2nd picture of that post (I think it's partly under the tag strip), but you can see it clearly in your picture. You sometimes have to be a bit careful when you mount replacement components in what would seem to be a neater and more sensible position from where the manufacturer originally fitted them, as instability can sometimes be caused, but in this case there was no problem. Obviously make sure the component is electrically connected to the original termination points.

[RoyceVM]

Originally Posted by Techman

Yes, it's not good practice to go too far over the top with the working voltage of an electrolytic capacitor. Most sellers will stock 63 volt working types as the modern preferred value for this application and you should go no higher than that. A quick look on-line shows both 22uf and 33uf electrolytic capacitors readily available at 63 volts working, but if you can get the exact 25uf value at around that working voltage, then that would be perfect. Make sure you get 'axial' types rather than the radial types.

Note that one of the 0.04uf brown Hunts capacitors that you need to replace is in an awkward position tucked away behind some resistors. Snip this capacitor out and once removed fit the replacement as I've done - it's the yellow one shown vertically on the right hand side of my 3rd picture in the previous post. You can't quite see the original one in my 2nd picture of that post (I think it's partly under the tag strip), but you can see it clearly in your picture. You sometimes have to be a bit careful when you mount replacement components in what would seem to be a neater and more sensible position from where the manufacturer originally fitted them, as instability can sometimes be caused, but in this case there was no problem. Obviously make sure the component is electrically connected to the original termination points.

Thanks so much for the advice and all your help. So grateful!
For some reason I haven't located the 5th 0.04uf brown Hunts cap you mentioned. Tomorrow morning, I will look for that one. I will be careful to put them all neatly connected. I have 5 SABA radios, one is a 13 valve autotuning and others too auto tuning ones, and several stereo Philips (7) radios in my collection that I fully recapped. I did it all like 10 years ago and have some experience but I am getting old. So, I need to be more careful. We had the same PYE model at home in 1966. I was blown away by the sound quality of it. It was a long wait to get one like it. I will be extra careful working on it.

[Ed_Dinning]

Hi Folks. C13/14 and R26/27, act as dampers across the output transformer. There was a discussion many years ago and I believe they are shown incorrectly on the circuit above. The should be connected between each anode and the HT , not to the screens as shown.
They can go leaky and cause all sorts of problems, seriously leaky and thy burn out the associated resistors. They damp out any ringing in the transformer that can cause insulation breakdown as well as reducing oscillations. I would use 630V devices here.

Ed

[RoyceVM]

Originally Posted by Techman

Yes, it's not good practice to go too far over the top with the working voltage of an electrolytic capacitor. Most sellers will stock 63 volt working types as the modern preferred value for this application and you should go no higher than that. A quick look on-line shows both 22uf and 33uf electrolytic capacitors readily available at 63 volts working, but if you can get the exact 25uf value at around that working voltage, then that would be perfect. Make sure you get 'axial' types rather than the radial types.

Note that one of the 0.04uf brown Hunts capacitors that you need to replace is in an awkward position tucked away behind some resistors. Snip this capacitor out and once removed fit the replacement as I've done - it's the yellow one shown vertically on the right hand side of my 3rd picture in the previous post. You can't quite see the original one in my 2nd picture of that post (I think it's partly under the tag strip), but you can see it clearly in your picture. You sometimes have to be a bit careful when you mount replacement components in what would seem to be a neater and more sensible position from where the manufacturer originally fitted them, as instability can sometimes be caused, but in this case there was no problem. Obviously make sure the component is electrically connected to the original termination points.

Thsnks! I located the paper caps you mentioned. What was the value of it? What was the value of the brown one on the right side that you didn't replace in your pic? Royce

[RoyceVM]

Originally Posted by Techman

Yes, it's not good practice to go too far over the top with the working voltage of an electrolytic capacitor. Most sellers will stock 63 volt working types as the modern preferred value for this application and you should go no higher than that. A quick look on-line shows both 22uf and 33uf electrolytic capacitors readily available at 63 volts working, but if you can get the exact 25uf value at around that working voltage, then that would be perfect. Make sure you get 'axial' types rather than the radial types.

Note that one of the 0.04uf brown Hunts capacitors that you need to replace is in an awkward position tucked away behind some resistors. Snip this capacitor out and once removed fit the replacement as I've done - it's the yellow one shown vertically on the right hand side of my 3rd picture in the previous post. You can't quite see the original one in my 2nd picture of that post (I think it's partly under the tag strip), but you can see it clearly in your picture. You sometimes have to be a bit careful when you mount replacement components in what would seem to be a neater and more sensible position from where the manufacturer originally fitted them, as instability can sometimes be caused, but in this case there was no problem. Obviously make sure the component is electrically connected to the original termination points.

I ordered 33uF/50V for replacing C11. I hope that is okay!

[RoyceVM]

Just replaced the 4 important caps.

[RoyceVM]

I got my PYE Black Box from UK with AC 240V and 50 cycles.
I am now looking for a 60 cycles pulley for the motor to use here in US.
For Black Boxes sold other than UK they supplied a 60 cycles pulley along with it. That pulley I need.