Hi folks,
I bought a old tube amp, based on the Maplin Millenium 4-20. Basically a Mullard 5-20 clone
It has big output transformers and a massive chrome chassis, so I think it's worth spending some time and money on it.
It has a powerful filter section, with 3x 200uf 500/600v filter caps.
I changed every electrolytic capacitor and the amp is working again. No hum, but a light overdrive on one channel using louder volumes. Tube swapping doesn't solve the problem - so maybe I need new sockets and maybe test some filter caps and resistors.
I found a page with some modifications of the Maplin, so I was wondering what these modifications do to the sound of the amplifier - maybe someone could tell me
thanks, and cheers,
Felix
I bought a old tube amp, based on the Maplin Millenium 4-20. Basically a Mullard 5-20 clone
It has big output transformers and a massive chrome chassis, so I think it's worth spending some time and money on it.
It has a powerful filter section, with 3x 200uf 500/600v filter caps.
I changed every electrolytic capacitor and the amp is working again. No hum, but a light overdrive on one channel using louder volumes. Tube swapping doesn't solve the problem - so maybe I need new sockets and maybe test some filter caps and resistors.
I found a page with some modifications of the Maplin, so I was wondering what these modifications do to the sound of the amplifier - maybe someone could tell me
thanks, and cheers,
Felix
What do you mean by a "light overdrive"? Do you mean early clipping?
The mods on that diagram are a mixture of good ideas and bad ideas. Good ideas:
1. remove bypass capacitors
Bad ideas:
1. remove 10M input resistor - this protects against failure of the volume pot. Even better, keep the resistor and add a coupling cap - this will lengthen the 'quiet' life of the pot.
2. remove the input low pass filter
3. swap the LTP to ECC81/12AT7 - this unbalances it so it then needs unbalanced anode resistors to push it back
4. reduce grid stopper values
5. fiddle with loop compensation components - this could be bad or good depending on the exact layout, OPT type etc.
The mods on that diagram are a mixture of good ideas and bad ideas. Good ideas:
1. remove bypass capacitors
Bad ideas:
1. remove 10M input resistor - this protects against failure of the volume pot. Even better, keep the resistor and add a coupling cap - this will lengthen the 'quiet' life of the pot.
2. remove the input low pass filter
3. swap the LTP to ECC81/12AT7 - this unbalances it so it then needs unbalanced anode resistors to push it back
4. reduce grid stopper values
5. fiddle with loop compensation components - this could be bad or good depending on the exact layout, OPT type etc.
Yes, I mean this shematic
Okay, so I wont went through the mods.
With overdrive I mean a distorted sound out of my speakers with rising volume level.
My speakers include a 15" Monacor SPA-115PA and a Celestion CDX-1430 horn driver - passive crossover network 8 Ohm overall impedance.
Changing tubes does not solve the problem - so I think it has something to do with the electric components.
Cheers,
Felix
Okay, so I wont went through the mods.
With overdrive I mean a distorted sound out of my speakers with rising volume level.
My speakers include a 15" Monacor SPA-115PA and a Celestion CDX-1430 horn driver - passive crossover network 8 Ohm overall impedance.
Changing tubes does not solve the problem - so I think it has something to do with the electric components.
Cheers,
Felix
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