A quick question about a Pye Black Box EL42 version - UK Vintage Radio Repair and Restoration Discussion Forum

Michael Maurice · 6th Mar 2018, 9:48 pm

I am refurbishing a Pye Black box.

My version is the EL42 version in ultra linear mode.

According to the manual the cathode resistor is 470R or (560R for the non ultra linear version) The tone control is 1K log

In the one I've got the cathode resistor measures around 220R, the resistor is discoloured to the point that the bands cant be made out, and the tone control is 5K.

The tone control is possibly a replacement but the cathode resistor is original.

What should I be fitting?

ukcol · 7th Mar 2018, 12:06 am

That is right Michael, the MK2 BBH should have a 470 ohm cathode resistor. As you probably know the output transformer in the BB has a reputation for failing and 220 ohms in that position is tempting fate. If you are not worried about originality under the chassis, a 470 ohm 5 watt wire-wound is probably a good plan because they don't change in value like the carbon resistors do.

A 560 ohm cathode resistor is only used in the MK1 in which the output pair are strapped as triodes.

With a 5 k tone pot you will probably find that its effect will be cramped to one end.

Boater Sam · 7th Mar 2018, 5:04 am

Try putting a 1K2 resistor across the 5K pot, is possibly lin too, it will give you nearly 1K log.

Michael Maurice · 9th Mar 2018, 2:00 pm

Fitted a new 1K pot with switch and a 470R resistor in the cathode circuit. All other parts replaced, it now works very well.

One other question, does anyone know the weight of the Pye black box fitted with this amplifier? The cabinet has gone for restoration and I need to know the weight for postage charges.

ukcol · 9th Mar 2018, 2:49 pm

My machine complete, (cabinet + changer + amplifier) weighs in at 14.7kg not including any packaging. No lightweight.

6th Mar 2018, 9:48 pm	#1
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	A quick question about a Pye Black Box EL42 version I am refurbishing a Pye Black box. My version is the EL42 version in ultra linear mode. According to the manual the cathode resistor is 470R or (560R for the non ultra linear version) The tone control is 1K log In the one I've got the cathode resistor measures around 220R, the resistor is discoloured to the point that the bands cant be made out, and the tone control is 5K. The tone control is possibly a replacement but the cathode resistor is original. What should I be fitting? __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/ Last edited by Michael Maurice; 6th Mar 2018 at 10:58 pm. Reason: wrong values put in

7th Mar 2018, 12:06 am	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: A quick question about a Pye Black Box EL42 version That is right Michael, the MK2 BBH should have a 470 ohm cathode resistor. As you probably know the output transformer in the BB has a reputation for failing and 220 ohms in that position is tempting fate. If you are not worried about originality under the chassis, a 470 ohm 5 watt wire-wound is probably a good plan because they don't change in value like the carbon resistors do. A 560 ohm cathode resistor is only used in the MK1 in which the output pair are strapped as triodes. With a 5 k tone pot you will probably find that its effect will be cramped to one end. Last edited by ukcol; 7th Mar 2018 at 12:17 am.

7th Mar 2018, 5:04 am	#3
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: A quick question about a Pye Black Box EL42 version Try putting a 1K2 resistor across the 5K pot, is possibly lin too, it will give you nearly 1K log.

9th Mar 2018, 2:00 pm	#4
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,225	Re: A quick question about a Pye Black Box EL42 version Fitted a new 1K pot with switch and a 470R resistor in the cathode circuit. All other parts replaced, it now works very well. One other question, does anyone know the weight of the Pye black box fitted with this amplifier? The cabinet has gone for restoration and I need to know the weight for postage charges. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

9th Mar 2018, 2:49 pm	#5
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: A quick question about a Pye Black Box EL42 version My machine complete, (cabinet + changer + amplifier) weighs in at 14.7kg not including any packaging. No lightweight.