Ekco P131MBQ (actually Pye) - UK Vintage Radio Repair and Restoration Discussion Forum

Celestial · 19th Nov 2023, 11:14 am

I have received this radio and have found that there has been some mods made to the original circuit. It seems that the metal rectifier has failed and been replaced by two IN4007 diodes with positive connected towards the transformer. The negative ends of the diode have been strapped together and connected through a 470 ohm resistor to chassis. I have measured across the original rectifier with my AVO Model 8 meter and I get a reading of 18k one way across the diodes and about 20k the other way.

Also, does anybody know the value of the resistance you should get across these metal rectifiers as I do not know anything about them?

I am not applying any power to the radio until this matter is resolved.

Many thanks.

Station X · 19th Nov 2023, 11:22 am

Not sure I understand your question. If the metal rectifier has been removed and replaced with silicon diodes why are you concerned about applying power? Is it your intention to refit the metal rectifier?

I don't have a circuit for this radio to check the original rectifier configuration. Are you sure it's not a Pye?

I've never had much luck testing metal rectifiers by measuring their resistance.

Station X · 19th Nov 2023, 11:30 am

Assuming it is a Pye the marked ends of the replacement diodes go to the transformer. The other ends are connected together and connected to chassis via a dropper resistor. The resistor compensates for the reduced forward volt drop of a silicon diode when compared with a metal rectifier.

Herald1360 · 19th Nov 2023, 11:33 am

A P131MBQ is Pye rather than Ekco, surely?

At any rate, the Pye service info shows the MR cathodes taken to the transformer secondary outers with HT+ from the secondary centre tap so the 1N4007 arrangement is fine.

Station X · 19th Nov 2023, 12:24 pm

Quote:

Originally Posted by Herald1360

A P131MBQ is Pye rather than Ekco, surely?

Yes that threw me when I initially looked for a circuit diagram. Better wait for confirmation from the OP before editing the thread title.

Herald1360 · 19th Nov 2023, 1:06 pm

Could be badge engineering, I guess? Was the P131MBQ still in production after 1960 when Pye and Ekco merged?

Celestial · 19th Nov 2023, 2:28 pm

Gentlemen,
I do apologise. My message should have read "PYE P131MBQ" and not Ekco P131MBQ"
I am very sorry for the error.

paulsherwin · 19th Nov 2023, 2:34 pm

Title updated.

smiler411 · 20th Nov 2023, 3:09 pm

you would need to disconnect the rectifiers to measure them properly as otherwise you are measuring resistance of whole circuit which would be similar both ways unless you use the diode test on your meter which applies a higher voltage than the basic resistance test this activate the diode by applying a suitable forward bias to turn it on (>0.7V). The sets bias resistances etc will still be in parallel with the diode so will never be higher than you measure now but then may be a lot lower one way

19th Nov 2023, 11:14 am	#1
Celestial Triode Join Date: Nov 2018 Location: Swindon, Wiltshire, UK. Posts: 43	Ekco P131MBQ (actually Pye) I have received this radio and have found that there has been some mods made to the original circuit. It seems that the metal rectifier has failed and been replaced by two IN4007 diodes with positive connected towards the transformer. The negative ends of the diode have been strapped together and connected through a 470 ohm resistor to chassis. I have measured across the original rectifier with my AVO Model 8 meter and I get a reading of 18k one way across the diodes and about 20k the other way. Also, does anybody know the value of the resistance you should get across these metal rectifiers as I do not know anything about them? I am not applying any power to the radio until this matter is resolved. Many thanks.

19th Nov 2023, 11:22 am	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,624	Re: Ekco P131MBQ Not sure I understand your question. If the metal rectifier has been removed and replaced with silicon diodes why are you concerned about applying power? Is it your intention to refit the metal rectifier? I don't have a circuit for this radio to check the original rectifier configuration. Are you sure it's not a Pye? I've never had much luck testing metal rectifiers by measuring their resistance. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Nov 2023, 11:30 am	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 20,624	Re: Ekco P131MBQ Assuming it is a Pye the marked ends of the replacement diodes go to the transformer. The other ends are connected together and connected to chassis via a dropper resistor. The resistor compensates for the reduced forward volt drop of a silicon diode when compared with a metal rectifier. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Nov 2023, 11:33 am	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,467	Re: Ekco P131MBQ A P131MBQ is Pye rather than Ekco, surely? At any rate, the Pye service info shows the MR cathodes taken to the transformer secondary outers with HT+ from the secondary centre tap so the 1N4007 arrangement is fine. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

19th Nov 2023, 1:06 pm	#6
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,467	Re: Ekco P131MBQ Could be badge engineering, I guess? Was the P131MBQ still in production after 1960 when Pye and Ekco merged? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

19th Nov 2023, 2:28 pm	#7
Celestial Triode Join Date: Nov 2018 Location: Swindon, Wiltshire, UK. Posts: 43	Re: Ekco P131MBQ Gentlemen, I do apologise. My message should have read "PYE P131MBQ" and not Ekco P131MBQ" I am very sorry for the error.

19th Nov 2023, 2:34 pm	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,124	Re: Ekco P131MBQ (actually Pye) Title updated.

20th Nov 2023, 3:09 pm	#9
smiler411 Tetrode Join Date: Apr 2008 Location: Rhondda Cynon Taff, Wales, UK. Posts: 85	Re: Ekco P131MBQ (actually Pye) you would need to disconnect the rectifiers to measure them properly as otherwise you are measuring resistance of whole circuit which would be similar both ways unless you use the diode test on your meter which applies a higher voltage than the basic resistance test this activate the diode by applying a suitable forward bias to turn it on (>0.7V). The sets bias resistances etc will still be in parallel with the diode so will never be higher than you measure now but then may be a lot lower one way