UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Reply
 
Thread Tools
Old 20th Nov 2023, 7:45 pm   #1
Gary5117
Triode
 
Join Date: Jun 2022
Location: Birmingham, West Midlands, UK.
Posts: 15
Default Pye P114BQ

Hi everyone.

I'm trying to understand radio schematics and I wondered if anyone could help with the description of this PYE radio cct in which it says the volume control acts as a diode load. What is a diode load, why do we need one? Your help is much appreciated.
Attached Thumbnails
Click image for larger version

Name:	Pie P114bq volume control IMG_20231116_175105546.jpg
Views:	61
Size:	40.1 KB
ID:	288466   Click image for larger version

Name:	IMG_20231120_173401386.jpg
Views:	44
Size:	47.7 KB
ID:	288467   Click image for larger version

Name:	IMG_20231120_173928155.jpg
Views:	56
Size:	79.1 KB
ID:	288468  
__________________
The more I find out, the more I know how much I don't know!
Gary5117 is offline   Reply With Quote
Old 20th Nov 2023, 8:22 pm   #2
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
Default Re: Pye P114BQ

Without a 'load', the AC signal rectified by a perfect diode would pass just half cycles of the AC carrier signal but in this circuit and without the 'load' it would discharge C18 leaving it to rest at a -ve DC corresponding to the AC carrier voltage peak. The volume control acts as a load on C18 and discharges the capacitor but slowly enough to filter out the unwanted carrier frequency but not fast enough to remove the audio.
PJL is offline   Reply With Quote
Old 21st Nov 2023, 3:10 pm   #3
Gary5117
Triode
 
Join Date: Jun 2022
Location: Birmingham, West Midlands, UK.
Posts: 15
Default Re: Pye P114BQ

Ah yes, that makes sense I put a capacitive dropper in a champion radio and couldn't understand why the rectified B+ wasn't getting up to the required voltage. It turned out that the capacitor was only working in part because it was also feeding the valve heaters which I guess were acting as a capacitive load....but not enough.
That is so helpful
Thank you
Gary
__________________
The more I find out, the more I know how much I don't know!
Gary5117 is offline   Reply With Quote
Old 21st Nov 2023, 3:32 pm   #4
Cobaltblue
Moderator
 
Cobaltblue's Avatar
 
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 6,756
Default Re: Pye P114BQ

If you have not already seen it there is some additional information on this subject here:

https://www.vintage-radio.com/repair...rf-stages.html

Including a nice drawing that shows what PJL describes.

A lot of good reading here:

https://www.vintage-radio.com/repair...ion/index.html

Cheers

Mike T
__________________
Don't care if it was a bargain why's it in my kitchen
Mike T BVWS member.
www.cossor.co.uk
Cobaltblue is online now   Reply With Quote
Old 21st Nov 2023, 3:56 pm   #5
Gary5117
Triode
 
Join Date: Jun 2022
Location: Birmingham, West Midlands, UK.
Posts: 15
Default Re: Pye P114BQ

In this cct is it also doing the same for C19?, and does the 10Mohm Resistor R8 do the same for C20?

Thanks
__________________
The more I find out, the more I know how much I don't know!
Gary5117 is offline   Reply With Quote
Old 21st Nov 2023, 3:58 pm   #6
Gary5117
Triode
 
Join Date: Jun 2022
Location: Birmingham, West Midlands, UK.
Posts: 15
Default Re: Pye P114BQ

Thanks Mike T I will have a look.
__________________
The more I find out, the more I know how much I don't know!
Gary5117 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 4:00 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.