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Old 18th January 2006, 06:57 PM   #1
Trebla is offline Trebla  United Kingdom
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Default 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?
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Old 19th January 2006, 06:58 AM   #2
nikita is offline nikita  Canada
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Default 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
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Old 19th January 2006, 07:11 AM   #3
Trebla is offline Trebla  United Kingdom
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Thanks Andre.
You have email.
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Old 20th January 2006, 04:31 AM   #4
nikita is offline nikita  Canada
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Default 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
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Old 20th January 2006, 08:10 AM   #5
EC8010 is offline EC8010  United Kingdom
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What will be left of the original amplifier after all these changes? The chassis?
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Old 20th January 2006, 11:47 AM   #6
SY is offline SY  United States
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You'll want to change that too- bad metal.
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Old 20th January 2006, 12:48 PM   #7
dhaen is offline dhaen  Europe
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Default Sorry...

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....
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Old 20th January 2006, 04:10 PM   #8
Trebla is offline Trebla  United Kingdom
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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.
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Old 21st January 2006, 09:15 PM   #9
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Who designed the ruddy thing in the first place ??????

richj
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Old 21st January 2006, 10:43 PM   #10
Trebla is offline Trebla  United Kingdom
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Quote:
Who designed the ruddy thing in the first place ??????
I don't think anyone's going to admit to that are they?
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