ampmadscientist
Well-Known Member
Long as I was answering questions, I posted the questions and answers here for future reference:
1. electlytic cap, ripple current is where the ripple start at? higher ampage rating is better?
Ripple current is how much AC the cap can take before it starts to overheat. If the rated current is higher the cap is more heavy duty.
So a higher rating is better. The continuous temperature rating is higher, and the cap may be bigger sized.
It's good to have a higher rating because it's made to last longer. But it is also more $ cost. (see page 10)
http://www.cde.com/resources/catalogs/AEappGUIDE.pdf
2. like b+ cap, some like 30uf stock is 50-50 parallel = 100uf. you used 100-100=200uf in few of my plexies. what does bigger uf mean? more available energy?
Yes, it takes the 200 twice as long to discharge compared to 100.
But this time is not very long, because there is load on capacitor. (like shorting out a cap to discharge it)
So this means the amp will have a little less sag with 200.
But the main purpose is to have less ripple in the power supply, so this means less hum in the output signal.
200 will have less hum than 100, but the change in sag will not be very much, just a tiny bit less.
There is really 2 sources of power supply noise
1. is ripple in the power supply = lowest frequency HUM
2. is Buzzing from the filament supply which is AC = Bzzzzzzzzzzzz noise, when volume is turned up.
AC filament is pretty noisy in Plexi. But there is ways to get rid of the noise by doing small mods.
3. stock bias caps are 8uf. i think you gave me 15uf and 20uf. what happen if 100uf is used?
It's better to use 10, 15 or 20 uF.
Cap has self resonant frequency, (page 10,11) and this will cause the amp to distort at low bass notes. It will sound muddy in the low frequencies.
http://www.cde.com/resources/catalogs/AEappGUIDE.pdf
100 sounds much more distorted than 10uF.
But, usually only trained musician can hear this difference! Technician who is not trained as musician will think there is no difference. (because they are tone deaf)
The factory used 8uF for this reason. They were trying to minimize the distortion.So, this is actually important reason.
Yes, trained ear can hear a big difference in the sound of the amp.Tone deaf hears no difference.
This is also important reason why technician should be musician, and guitar player. Tech cannot tell if amp sounds right, unless they are experienced and trained in music.
4. his two of jmp 50w are not so bad as they just need few issues sorted out but his jtm45 the bias voltage going way high-low way high swinging. oh man, do you knopw what could be? it could be anything hahaha!!!
It's usually an old capacitor...
A. Bias filter caps are old, might be bad
B. Bias rectifier diode may be bad
C. Bias pot can be bad
D. Resistor in bias circuit may be bad
E. There can be bad tube socket, insulation is bad between pin 5 and 4...or between pin 5 and 6.
Measure the old parts...Try new parts until the bias is holding very steady.
5. and you know those 50w standby sw issue? groove guy tells you to hook up bias feed from cold to hot of standby sw. what does this mean?
Yes this is a factory mistake.
Bias voltage does not turn on until standby is ON.
The wire should be moved to the other side of the standby switch. (move wire to the hot side of switch)
Then - bias voltage will be ON, BEFORE standby is turned ON.
Then there will be less power surge when standby is turned ON. Tube will not surge as much. This is a good thing, tube will probably last longer.
6. ONE last thing - screen grid resistors. IMPORTANT:
Check to see if the screen grid resistors are installed. In old Marshalls there may not be screen grid resistors.
EL34 = 1K 6L6 or KT66 = 470 ohm
The screen grid resistors MUST be installed. This is NOT optional.
If there is no screen grid resistor, the tube will draw too much current. This can cause the tube to blow, or the fuse will blow, or the power transformer might overheat.
Reason: the design of the tubes were changed. NEW tube draws more current than OLD style tube.
The resistor is required to limit the screen grid current - NOT optional.
(when the power transformer fries, you will wish that the screen resistor was installed, I warned YOU.)
1. electlytic cap, ripple current is where the ripple start at? higher ampage rating is better?
Ripple current is how much AC the cap can take before it starts to overheat. If the rated current is higher the cap is more heavy duty.
So a higher rating is better. The continuous temperature rating is higher, and the cap may be bigger sized.
It's good to have a higher rating because it's made to last longer. But it is also more $ cost. (see page 10)
http://www.cde.com/resources/catalogs/AEappGUIDE.pdf
2. like b+ cap, some like 30uf stock is 50-50 parallel = 100uf. you used 100-100=200uf in few of my plexies. what does bigger uf mean? more available energy?
Yes, it takes the 200 twice as long to discharge compared to 100.
But this time is not very long, because there is load on capacitor. (like shorting out a cap to discharge it)
So this means the amp will have a little less sag with 200.
But the main purpose is to have less ripple in the power supply, so this means less hum in the output signal.
200 will have less hum than 100, but the change in sag will not be very much, just a tiny bit less.
There is really 2 sources of power supply noise
1. is ripple in the power supply = lowest frequency HUM
2. is Buzzing from the filament supply which is AC = Bzzzzzzzzzzzz noise, when volume is turned up.
AC filament is pretty noisy in Plexi. But there is ways to get rid of the noise by doing small mods.
3. stock bias caps are 8uf. i think you gave me 15uf and 20uf. what happen if 100uf is used?
It's better to use 10, 15 or 20 uF.
Cap has self resonant frequency, (page 10,11) and this will cause the amp to distort at low bass notes. It will sound muddy in the low frequencies.
http://www.cde.com/resources/catalogs/AEappGUIDE.pdf
100 sounds much more distorted than 10uF.
But, usually only trained musician can hear this difference! Technician who is not trained as musician will think there is no difference. (because they are tone deaf)
The factory used 8uF for this reason. They were trying to minimize the distortion.So, this is actually important reason.
Yes, trained ear can hear a big difference in the sound of the amp.Tone deaf hears no difference.
This is also important reason why technician should be musician, and guitar player. Tech cannot tell if amp sounds right, unless they are experienced and trained in music.
4. his two of jmp 50w are not so bad as they just need few issues sorted out but his jtm45 the bias voltage going way high-low way high swinging. oh man, do you knopw what could be? it could be anything hahaha!!!
It's usually an old capacitor...
A. Bias filter caps are old, might be bad
B. Bias rectifier diode may be bad
C. Bias pot can be bad
D. Resistor in bias circuit may be bad
E. There can be bad tube socket, insulation is bad between pin 5 and 4...or between pin 5 and 6.
Measure the old parts...Try new parts until the bias is holding very steady.
5. and you know those 50w standby sw issue? groove guy tells you to hook up bias feed from cold to hot of standby sw. what does this mean?
Yes this is a factory mistake.
Bias voltage does not turn on until standby is ON.
The wire should be moved to the other side of the standby switch. (move wire to the hot side of switch)
Then - bias voltage will be ON, BEFORE standby is turned ON.
Then there will be less power surge when standby is turned ON. Tube will not surge as much. This is a good thing, tube will probably last longer.
6. ONE last thing - screen grid resistors. IMPORTANT:
Check to see if the screen grid resistors are installed. In old Marshalls there may not be screen grid resistors.
EL34 = 1K 6L6 or KT66 = 470 ohm
The screen grid resistors MUST be installed. This is NOT optional.
If there is no screen grid resistor, the tube will draw too much current. This can cause the tube to blow, or the fuse will blow, or the power transformer might overheat.
Reason: the design of the tubes were changed. NEW tube draws more current than OLD style tube.
The resistor is required to limit the screen grid current - NOT optional.
(when the power transformer fries, you will wish that the screen resistor was installed, I warned YOU.)
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