Vintage Maplin 50W Amplifier and Pre-amp Kit - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th May 2017, 12:48 AM   #1
roclite is offline roclite  United Kingdom
diyAudio Member
 
Join Date: Dec 2011
Location: Middlesex
Send a message via Skype™ to roclite
Default Vintage Maplin 50W Amplifier and Pre-amp Kit

I just couldn't resist rescuing this assembled Maplin 50W amplifier kit on eBay, harking back to the good old days when Maplins were educational and before they started to sell crate-loads of Chinese junk. The seller had stripped the boards and transformer out of a poorly-built amplifier chassis and looking at the boards, you can probably understand why. I don't think the original constructor had too much idea and the amplifier boards are assembled badly with a mish-mash of different components e.g carbon, carbon film and metal film, vintage 1978 capacitors and flying-lead transistors. Clearly, his electronics scrap box was raided as the component source. The pre-amp board is not too bad and can be used as is but I will completely strip down the amplifier boards and start again with new components, taking the opportunity to use lower noise transistors and improve the capacitor decoupling. I have all the other components required already so lets hope I can get this amplifier up and running soon before I get too teary-eyed with nostalgia
Attached Images
File Type: jpg RIMG0163.jpg (965.3 KB, 215 views)
File Type: jpg RIMG0164.jpg (883.9 KB, 209 views)
File Type: jpg RIMG0165.jpg (976.4 KB, 191 views)
  Reply With Quote
Old 18th May 2017, 08:40 AM   #2
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Horrible little amplifier!
The schematics are available here https://www.scribd.com/doc/38418078/...35Q-Maplin-Kit
Have fun.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 18th May 2017, 08:48 AM   #3
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Not sure horrible is the right word tbh. It was quite an advanced (for diy) design back in the day.
  Reply With Quote
Old 18th May 2017, 09:05 AM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I'm pretty sure this, or one very similar, has a Thread dedicated to it.

Remove those plastic bolts and replace with insulating "tophats" and steel bolts/screws/studs.
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 18th May 2017, 09:09 AM   #5
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Can someone tell me/us how to run the three wires to the remote power devices?
a.) Twist all three?
b.) Twist Collector and Emitter and keep Base separate, but close, c.) base farther away?
d.) Run all three parallel with no gaps and base on the inside, or e.) Collector on the inside or f.) Emitter on the inside?
g.) Keep all three parallel but separated by 3mm again which (h & i) on the inside?
j.) Other options?
__________________
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 18th May 2017, 09:32 AM   #6
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Quote:
Originally Posted by Mooly View Post
Not sure horrible is the right word tbh. It was quite an advanced (for diy) design back in the day.
The reason why it was known as 'horrible' was down to the power transistor fixings coming loose. Just a poor finish but as you say, quite advanced for the 80s.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 18th May 2017, 09:55 AM   #7
roclite is offline roclite  United Kingdom
diyAudio Member
 
Join Date: Dec 2011
Location: Middlesex
Send a message via Skype™ to roclite
Andrew T, thanks for the steer on similar threads. I want to completely re-build as per the original design but substitute better rated transistors/resistors and avoid instability problems. My nostalgia doesn't extend as far as trashing my JBL speakers.
  Reply With Quote
Old 18th May 2017, 12:17 PM   #8
diyAudio Member
 
Join Date: Jun 2010
Quote:
Originally Posted by AndrewT View Post
Can someone tell me/us how to run the three wires to the remote power devices?
All three twisted is probably ok in most power devices. The capacitative coupling of the B to C would be small in relation to the intrinsic capacitance of the device and the current loop would be the smallest.
  Reply With Quote
Old 18th May 2017, 12:20 PM   #9
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hard wiring T03 devices to PCB's was common many years ago. Just look at old photos in service manuals and the like to see how it was done back then.
  Reply With Quote
Old 18th May 2017, 12:29 PM   #10
diyAudio Member
 
Join Date: Mar 2014
I have one of those. In less good state tho. I do mean to get it running again one day...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
TP2050 Class-D Power Amplifier Board [50W + 50W] Agustr Class D 5 15th May 2016 03:25 PM
Maplin 100w mosfet amplifier built from 1980 kit nigelwright7557 Solid State 34 11th December 2015 12:40 AM
75 Watt Vintage Bell Amplifier - pre amp ? Gary Vee Instruments and Amps 9 6th February 2014 05:26 PM
Feedback arrangement in vintage 50W amplifier richard8976 Solid State 6 8th December 2010 09:25 AM


New To Site? Need Help?

All times are GMT. The time now is 07:17 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki