Maplin 4-20

Trebla · 18th January 2006, 06:57 PM

I have an amp which I think is a version of the Maplin 4-20.
I know these are not highly regarded but since it works ok, I thought I might try one or two basic upgrades.
Obviously I'm not going to throw a lot of money at this, but a few component changes might be interesting.
I believe it might be based on the Mullard amps but i'm not sure how closely.
Problem is I don't have a schematic nor can i find one. Can anyone help?

nikita · 19th January 2006, 06:58 AM

I have the schematic of the Maplin 4-20 , Give me your EM and I will send it to you. BTW, It's based on the Mullard 5-20 and I have that one too.
Andre

Trebla · 19th January 2006, 07:11 AM

Thanks Andre.
You have email.

nikita · 20th January 2006, 04:31 AM

HI Al, now that you have the shematic, let see what you can do.
1-Change the tubes for better quality ones (some brands are better than others in specific fonctions)
2_Change resistors and capacitors (in the signal path at least) for higher grade.
3-Change the transfos for better ones (this is the weakest piont in this amp, no real bass, strident highs and lack of dynamics) Could be costly but you'll get the greatest improvement.
4- Change the SS rectifier for a tube rectifier (could be complicated!)
Good luck !
Andre

EC8010 · 20th January 2006, 08:10 AM

What will be left of the original amplifier after all these changes? The chassis?

SY · 20th January 2006, 11:47 AM

You'll want to change that too- bad metal.

dhaen · 20th January 2006, 12:48 PM

Quote:

Originally posted by EC8010
What will be left of the original amplifier after all these changes? The chassis?

The chassis is a bit cramped, so it gets rather too hot

I've commented on these OP transformers before.....

The grid leaks of the EL34's are a bit too high at the anode voltage used.
It goes on....

Trebla · 20th January 2006, 04:10 PM

Quote:

What will be left of the original amplifier after all these changes? The chassis?

Thats about all. Mind you the sockets on the back are pretty good!
I know the trafos are the weakest link, but i'll only change these if i find something secondhand.
I've already fitted a new quad of EH tubes which was money well spent.
As for the rest of it ......
Cap changes etc, no problem.

richwalters · 21st January 2006, 09:15 PM

Who designed the ruddy thing in the first place ??????

richj

Trebla · 21st January 2006, 10:43 PM

Quote:

Who designed the ruddy thing in the first place ??????

I don't think anyone's going to admit to that are they?

18th January 2006, 06:57 PM	#1
Trebla diyAudio Member Join Date: Nov 2005 Location: North West	maplin 4-20 I have an amp which I think is a version of the Maplin 4-20. I know these are not highly regarded but since it works ok, I thought I might try one or two basic upgrades. Obviously I'm not going to throw a lot of money at this, but a few component changes might be interesting. I believe it might be based on the Mullard amps but i'm not sure how closely. Problem is I don't have a schematic nor can i find one. Can anyone help?

19th January 2006, 06:58 AM	#2
nikita diyAudio Member Join Date: Dec 2004 Location: Montreal, Canada	Maplin 4-20 I have the schematic of the Maplin 4-20 , Give me your EM and I will send it to you. BTW, It's based on the Mullard 5-20 and I have that one too. Andre

20th January 2006, 04:31 AM	#4
nikita diyAudio Member Join Date: Dec 2004 Location: Montreal, Canada	Maplin 4-20 HI Al, now that you have the shematic, let see what you can do. 1-Change the tubes for better quality ones (some brands are better than others in specific fonctions) 2_Change resistors and capacitors (in the signal path at least) for higher grade. 3-Change the transfos for better ones (this is the weakest piont in this amp, no real bass, strident highs and lack of dynamics) Could be costly but you'll get the greatest improvement. 4- Change the SS rectifier for a tube rectifier (could be complicated!) Good luck ! Andre

20th January 2006, 08:10 AM	#5
EC8010 diyAudio Moderator Emeritus Join Date: Jan 2003 Location: Near London. UK	What will be left of the original amplifier after all these changes? The chassis? __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

20th January 2006, 11:47 AM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	You'll want to change that too- bad metal. __________________ If there's a sucker born every minute, where do the rest of them come from?


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19th January 2006, 07:11 AM	#3
Trebla diyAudio Member Join Date: Nov 2005 Location: North West	Thanks Andre. You have email.

21st January 2006, 09:15 PM	#9
richwalters diyAudio Member Join Date: Sep 2003 Location: Alps:Tube amp designs over 150W, SMPS guru.	Who designed the ruddy thing in the first place ?????? richj

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