Pye black box no sound

[Minster97]

Only very occasionally is there any sound when you strum the pick up although the speakers are humming all the time.I started by replacing all Hunts capacitors,checking the electrolytics and resistors.Checked resistance on both transformers,output spot on but mains a little low.
Only one of the El42’s glows and gets hot,the one next to the rectifier.I replaced the valve (nearer to the triode) with a NOS valve and this doesn’t get hot either,I can see no glow.
Would appreciate any help please

[Station X]

The fact that some valves light up shows that the LT supply is working correctly.

Failure of valves to light up will be down to dirty valve pins or dodgy valve sockets.

See post #60 in this thread:-

https://www.vintage-radio.net/forum/...d.php?t=176679

[Sideband]

Very very common to have faulty valveholder pins. The heater pins for the EL42 are pins 1 & 8. It might be possible to just change the pins.....there will be some unused ones in the rectifier valveholder. Otherwise it will mean changing the valveholder. These are still available from suppliers like Langrex.

I had a mammoth task on one of these amplifiers where I had to change nearly every pin. If I'd known from the start it probably would have been quicker to change the valveholder.

[Minster97]

Thank you all,I have cleaned and now both valves are equally hot.However there is still nothing from the pick up.I have prodded the entire length of wire to the record deck and not a murmur!

[Chris55000]

Hi!

Do you have a digital multimeter? You will need one to identify this fault further as there could be an earlier stage valve not functioning!

Is there a faint hum from the loudspeaker when you turn the volume control up full?

You will also need the Service data which can be bought from the button at the top of every page - but please note there were several "Black Box" models, the later ones had two PCL83 valves and are totally different from the model you have!

Chris Williams

[BRASSBITS]

Originally Posted by Minster97

Thank you all,I have cleaned and now both valves are equally hot.However there is still nothing from the pick up.I have prodded the entire length of wire to the record deck and not a murmur!

it could be a dead cartridge, have you tried the buzz test?

[Minster97]

There is a constant low hum from speakers which stays the same whether volume down or up.
I did buy the circuit diagram and have multimeter. Don’t know what buzz test is.

Thank you.

[Station X]

Buzz Test.

Volume at max.

There's socket on the amplifier where the signal wires from the pick up plug in. Remove the plug MAKE SURE IT'S THE RIGHT ONE!, then touch the unearthed socket, which you removed the plug from, with a screwdriver blade. A loud buzz indicates that the amplifier is working.

[Chris55000]

Hi!

If you touch the contacts at the back of the pickup cartridge with a small screwdriver, this will pick the a.c. magnetic field around the screwdriver that will be injected into the amplifier as a low 50 Hz voltage that will be amplified to produce a "buzz" in the loudspeaker, hence the term "buzz test".

There should be virtually no direct voltage on the back of the pickup cartridge contacts, this test is normally quite safe to carry out in most players!

A very faint or no response indicates either a disconnection between the cartridge and the connection tag-strip underneath the turntable chassis, or the early stages of ther amplifier are not functioning! These leads between the pickup and the underside connection tag-strip are very fine and liable to break easily.

Many pickup cartridges are slightly microphonic, and most good record players will produce lively rustling noises, clicks or pops in the loudspeaker if you touch or tap the pick-up arm head near the cartridge head!

If you post a picture of the underside chassis of the amplifier I can mark on it for you what voltages to test if need be!

Chris Williams

[Minster97]

Hi again.Buzz test negative.I removed the pick up input and prodding produced no response.
On occasions as I said there was sound from the pick up.After I bought it,it played the record very quietly and then sound sent altogether.
Photo of amp
Regards Gary

[Station X]

Time to take some voltage readings as described in post #38 onwards in this thread:-

https://www.vintage-radio.net/forum/...d.php?t=176679

[Herald1360]

Some very familiar pictures

Likely nothing directly to do with your no sound problem, but do check that 470R resistor that looks like it's been a bit sweaty- it's the cathode bias resistor for the output pair. Mine had gone low which isn't good news for the valves nor the output transformer.

[Minster97]

Thank you.Will study all this and do my best.My shed is on an RCD circuit but I am going to get an isolation transformer as well.I presume that there are no compatibility issues using the two together?

[Minster97]

Chris the sweaty 470ohm resistor is cut off. Difficult to see on the photo. I wired four 2200 ohm in parallel instead as it said needs half a Watt and all my resistors say 1/8 watt. thank you

[ajgriff]

An isolation transformer isolates things from the RCD too. Do some forum seaches on 'isolation transformer'. Can be a controversial subject.

Alan

[Minster97]

Resistance reading does more or less spot on

[Herald1360]

Half a watt is sailing close to the wind for that 470R. If the output valves are running at precisely the design current, it'll dissipate right on its limit. If you must use 1/8W parts, I'd suggest 7*3.3k (471R) rather than 4*2.2k (550R) though that 550R would bias the valves a fair bit lower on anode current, reducing the dissipation along with output power too.

I've got another 470R W22 6W wirework like the one in my recent Black Box thread picture if you're interested at the cost of a large letter. Physically it's pretty much the same size as the old 1/2W carbon job, electrically in the application, just about bombproof!

[Sideband]

Going back to my post #3 it wouldn't surprise me at all if the pins in the socket for the ECC82 (83?) are faulty. I certainly had this problem with the amp I serviced some years ago and it would give you the no results with the 'buzz' test. Voltage readings should reveal all.

[Techman]

Originally Posted by Minster97

Chris the sweaty 470ohm resistor is cut off. Difficult to see on the photo. I wired four 2200 ohm in parallel instead as it said needs half a Watt and all my resistors say 1/8 watt. thank you

I would take up the kind offer from Chris in post #17 for a proper resistor

As for isolation transformers, I've got several of different sizes and never use them, unless I need to for a specific reason - learn to work safely without one. If you read through the couple of recent threads where people have asked about isolation transformers and their usage, you'll probably lose the will to live!

[Minster97]

Readings for the two capacitors are 275V and 236V
Output transformer all three readings are 275V
I am fairly sure that the valve holder for ECC83 is ruined.
The readings for Ecc83 are pin 1 zero,pin 3 69V,pin 6 zero or very slightly minus,pin 8 zero
I could see the wider gap between the pins so think I got the numbering right.
Now the EL42’s,There was a wire going across the opening to a pin at about the four or five o’clock position,I have assumed this is pin 8
Readings for both valves are the same.pin 2 16V,pin 3 0.2 V , pin 5 zero pin 6 15.7V
I am very lost now.I suppose I have got to start by replacing the valve holder?? but not sure what is the correct one.Thank you