Pye Black Box PCL83 version

[Heatercathodeshort]

'The master'.. Ha! Ha! I get a vision of a Jimmy Edwards character...Nice one!

Until recently I used to leave the odd paper capacitor in circuit if it was in no way critical. Some of the solid Hunts and GEC types faired reasonably well but these components are now 60+ years old, 50 years past their original design life. They leak, particularly when warm, increase in value and cause circuit chaos.

Oddly the main smoothing blocks hold up very well and over the years I have replaced very few in vintage television receivers. It appears these are ripped out in an attempt to cure low level hum problems that was a character of these very basic players.

The simple but very efficient UL84/UY85 arrangement replaced the simple acoustic gramophone of my parents generation [teenagers in 1930] if they could have afforded one that is.

The PYE Black Box gives a very good account of itself particularly the original version with EL42 valves in push pull. Replace all the leaky paper caps and fit a stereo compatible cartrtridge and providing the output transformer has not become O/C you will have a very nice record player suitable for all but your rare classic LP stereo records.

The PCL83 version sounds good when working correctly but why on earth PYE employed these highly strung triode pentodes with .3amp odd voltage heaters is very strange. I can only imagine they had thousands left over from the V14 and other models of television production and cobbled together the amp that appears in the later Black Box.

A very thorough overhaul is required to guarantee a reliable result including replacement of all paper type capacitors, coupling etc. The PCL83 does not like to be overrun and is best operated at a slightly lower HT. Care has to be taken when replacing the contact cooled rectifier allowing for the lack of a voltage drop when replacing it with silicon diodes.

Don't write off the excellent BSR decks employed in many of these players. They do not harm records! Can you imagine a top of the class manufacturer fitting record decks that damaged customers records?

They are not 'HiFi' by today's standards but still give a very good account of themselves.
They will play all your records, 78's 45's LP's and with a suitable medium output cartridge, non rare and precious stereo LP's.

Have fun! Regards, John.

[vampyretim]

Hi,

I've now replaced all paper caps and installed nos PCL83's but I still have annoying hum. I seem to be battling hum and hiss in a lot of these old valve amps at the moment.

Any ideas where I should start looking?

[Station X]

Originally Posted by vampyretim

I checked power supply caps which were fine.

I assume you mean the smoothing and reservoir caps. How did you check these?

[vampyretim]

It's not the power supply caps, I've replaced them now anyway.

[John10b]

I’ve been following this thread with great interest. I’m in the process of serving the el42 bb version, you might find that thread interesting. I’m surprised that even after all your efforts you are still having problems with hum etc. The bb I’m working on has virtually no hum.
Any way good luck in finding a solution.
Cheers
John

[vampyretim]

I've got this across R23, looks weird.

[leslie5555]

I have in the past found on some of these a poor earth between the smoothing cap and the chassis can contribute to the hum.
Removing the cap and cleaning around the area where the cap makes contact with the chassis with some abrasive paper will improve the earth contact.
However take care when re tightening the nut as the base of the cap is brittle and can fall to bits if over tightened (guess how I know that)

[vampyretim]

I'm getting really annoyed with this, I'm tracing hum right back to the the tone pot. I've cleaned up power supply caps earthing point but it's not that. I sometimes hate electronics!!

[leslie5555]

Broken forks in the valve bases is also something that can cause humming, replacing them with good ones has cured humming.
I have just finished restoring a pye black box mark two amp took me six weeks to finally sort it out including having the output TX rewound by Ed Dining and replaced lots of components and broken valve forks and the end result is an amp with no humming and sounds very good.
It can try your patience but if you stick at it you will get there in the end.

[vampyretim]

It doesn't have the fork type pin grips. I'm getting 35 mV of 100hz hum at the speakers. It's quite audible but I'm wondering if it's the bed that can be done. Surely I shouldn't have the scope image that I've got at the speakers ?

[John10b]

What happens when you adjust the bass (tone)pot fully both ways?
Cheers
John

[John10b]

Sorry I ment to ask also what is on the grid of the other valve V3b?
Cheers
John

[vampyretim]

Originally Posted by John10b

What happens when you adjust the bass (tone)pot fully both ways?
Cheers
John

Hi John,

It deforms the already deformed sine wave. What are your thoughts?

I'll check voltage tomorrow.

[John10b]

Just Wondering where it originates. The Phase splinter driving the two output grids of V2b and V3b, it would be interesting to see what’s on the two grids.