Pye Black Box Restoration

[OldTechFan96]

Hello,

Recently I bought a Pye Black Box as a project for over the winter. It is in decent cosmetic condition. The 'Hi Fi' badge is missing the 'F' and unfortunately I could not find it amongst the packaging. The speed selector knob is broken and will need to be glued back together.

So far I have gave the cabinet, amplifier and BSR turntable a good clean.

I'm not too sure which model of BB this is. I can't find any dates inside the cabinet or on any components. The valve lineup is: EL42*2, EZ41, and a ECC8?. I can't make out the markings on the last valve. I've been using Trader Sheet 1360.

I intend to replace all of the paper HUNTS capacitors and the smoothing capacitors. Of the paper capacitors two are 0.0047uf and one is 0.0022uf. My local component shop does not stock these values. Would it be all right to use 0.047uf and 0.022uf paper capacitors instead?

Before I replace any capacitors I would like to test the transformers. The mains transformer checks out OK with my DMM against the values on the TS 1360. I'm not sure about the O/P transformer. Should points A to D measure 1600 ohms? Is it measured from the cathode of V2 to the cathode of V3?

Thanks for reading.

[Boater Sam]

Those capacitor values are 10 times higher value than what you require!
There are plenty of suppliers who will have the correct value, and AT THE CORRECT OR GREATER WORKING VOLTAGE. Maplins? RS? ebay?
Can I suggest that before changing anything, that you establish that it is working? Then if it doesn't after you have change ONE capacitor, you know you have made a mistake and where that mistake is. Check after every change.
Changing parts willy nilly has destroyed many sets and discouraged many owners.

[ms660]

Originally Posted by OldTechFan96

Before I replace any capacitors I would like to test the transformers. The mains transformer checks out OK with my DMM against the values on the TS 1360. I'm not sure about the O/P transformer. Should points A to D measure 1600 ohms? Is it measured from the cathode of V2 to the cathode of V3?

So far as I can make out from the Trader sheet, A to D aren't measuring points for the primary, they're the winding sections, the resistance figure given will be for the total of all those sections, in other words the resistance between the two anode connections for V2 & V3, which I think are the uppermost and lowermost tags of the tags on the right hand side of the output transformer as viewed in the photo you posted.

Lawrence.

[Michael Maurice]

Originally Posted by Boater Sam

Can I suggest that before changing anything, that you establish that it is working? Then if it doesn't after you have change ONE capacitor, you know you have made a mistake and where that mistake is.

Sorry Sam, I cant agree with you. Those output transformers are fragile enough without you putting extra current through them because the coupling are faulty.

You check the O/P transformer anode to anode or better still Centre tap to each anode. There will be differences between the readings on each leg but dont worry about that.

Take lots of pictures, make notes. Draw out that tag strip and note where every component goes before removing them.

Remove the wires from the capacitors in the can, undo the nut, and clean the capacitor can where it meets the chassis also the chassis, refit the capacitor and tighten the nut and refit the wires.

I have highlighted the capacitors you need to change and the resistors you need to check, there are more but there are hidden.

Only when you've done this should you switch on.


Double check your work before switching on.

[Ed_Dinning]

Hi, the transformers don't look fried, so you may be lucky. Plenty of nasty Hunts to change, but the e-caps are usually OK on these sets.
Also look out for resistors that have gone high in value; ones that have gone a bit low may only be because they are connected to a leaky cap.
These units sound quite nice when working.
Agreed with the comments about the transformers, they are worked very hard, I have had to rewind quite a few of them.

Ed

[Edward Huggins]

Your version is the BBH. The valve is a ECC83. There were 2 versions of this model. The earlier 1954 model has the EL42s triode connected, in the later 1955 version they are ultra-linear configured with a slightly more powerful output. Given this, there is a difference in the OPTX.

[leslie5555]

The OP's version is the mark two

[OldTechFan96]

Thanks for all of the information! I've found all of the correct capacitor values at http://oldradioshop.co.uk. I can't complete the order because the 'Verify you are a human' section is empty. There is no captcha to complete.

There is no contact information on the website. Does anybody have a contact E-Mail address?

[Nuvistor]

That page returns a 403 forbidden error for me.

Have you seen this sticky item in the forum?

https://www.vintage-radio.net/forum/...ad.php?t=55701

[OldTechFan96]

The correct URL is: http://oldradioshop.co.uk/shop/

I'll have another look at the sticky. I think I found the above supplier in there.

[Nuvistor]

I see what you mean about the “verify you are a human “ section, blank for me when I just tried it.
Plenty other suppliers available.

[OldTechFan96]

I've been able to order the components I require through Cricklewood Electronics.

When measuring the resistance between the anodes of V2 and V3 my DMM's reading fluctuates a bit then settles on .02 ohms. When I test for continuity my DMM beeps.

When I measure the resistance between the uppermost and lowermost points of the O/P transformer my DMM reads O/L.

I'll do some more readings later on and report back.

[ms660]

It can be easy to get the cathode and anode confused if you read the valve holder connections for the EL42 the wrong way round....Pin 2 is anode pin 7 is cathode...follow the wires from the output transformer.

Lawrence.

[Boom]

Originally Posted by OldTechFan96

Thanks for all of the information! I've found all of the correct capacitor values at http://oldradioshop.co.uk. I can't complete the order because the 'Verify you are a human' section is empty. There is no captcha to complete.

I get this sometimes with Firefox. Switching to IE usually allows an input but it's very strange why it does it.

[OldTechFan96]

I followed the wires from the O/P transformer and measured the resistance between the two valve holder tags. The resistance was 530K ohms and rising.

It looks like the transformer could be OK.

The next thing I'll look into is replacing is the rubber turntable motor grommets that have perished.

[ms660]

Something wrong there then.

Lawrence.

[simpsons]

Looking at earlier threads on this site, the first check must be to T1 whose failure is likely to be caused by C5. To check if the transformer is OK logic suggests that the resistance from the centre tap, shown where R16 is connected, should be the same to both anode connections viz pin 2 of the EL42 and the screen connection viz pin 5. That is, either side of the centre tap on the transformer. I don't have exact values but often this will be in hundreds of ohms not thousands with the anode resistance being higher.

Once confirmation that the output transformer is OK, change C5 & 6 before switching on. Conversion from microfarads quoted to nano farads etc can be found online but for C5/6 this is 5n and as said earlier, don't change everything just yet although unfortunately Hunts capacitors are bad news.

Hope this helps

Chris

[OldTechFan96]

Today I have been trying to make the resistance measurements suggested by Michael Maurice and simpsons to check out the O/P transformer.

The thing that confuses me is that the resistances measured are in M ohms (ranging from 5 to 55M ohms). Only two measurements are in ohms. Surely the resistances I'm measuring should not be that high? I was expecting only hundreds of ohms.

I'll find my old DMM and make the measurements again.

[ms660]

The total resistance given in the Trader sheet between the anode connections on the transformer is 1,600 Ohms, the resistance from either of those connections to the centre tap will be approx. half of that, if the meter is ok and your getting a reading of Megohms then that suggests that the transformer is shot.

Lawrence.

[OldTechFan96]

I agree that the output transformer is shot. Would it be worth powering up the amp once the suspect capacitors are replaced despite the bad output transformer?

I'll have to replace or rewind the transformer.