The schematic(http://www.preservationsound.com/wp-content/uploads/2011/09/Mullard_520_schem.jpg ) asks for choke with 8H 180 mA. (no voltage given).This is the power transformer I am buying(https://www.edcorusa.com/xpwr011) but I can't find the CHOKE. Edcor has two
CXC125-10H-200mA
which is better to do given schematic: go UP to 10H or go DOWN 8H ?
- CXC100-7H-150mA
CXC125-10H-200mA
which is better to do given schematic: go UP to 10H or go DOWN 8H ?
Don't worry about the exact inductance. Far more important is the resistance and current rating. Does the circuit require 180mA, or was that just the choke which was available to the original designer?
C13 makes this a capacitor input filter.
That makes the inductance of L1 much less important.
Get the right current rating.
Note the 25Vdrop across the 145r inductor.
That tells you the current is ~172mA.
You need at least that rating.
You could replace the inductor with a resistor and the PSU would still work.
adding some capacitance might be a lot cheaper than buying an inductor.
The sch presently shows an rC(L+R)C
You could change that to rCRC, or for more ripple attenuation to rCRCRC.
8uF 500V caps are MUCH cheaper than 7H, or 8H inductors.
r= existing resistance upstream of C13.
C=8uF
In the new
C= 8uF or 10uF, 3off
R= 68r or 75r, 5W or 7W, 2off
Consider an extra resistor before C13 if you increase the capacitance to reduce the load on the valve rectifier, i.e. increase r.
It could be better to stagger the C value.
add 22r (3W, or 5W)upstream of C13. Change C13 to 5uF or 6uF
fit a 68r instead of L1
add an extra capacitor after L1, use 5uF or 6uF
fit a 68r as an extra resistor.
C12 becomes 10uF or 12uF (or two of the previous in parallel
this gives RCRCRC PSU which you can model in PSUD2
and compare to existing sch.
That makes the inductance of L1 much less important.
Get the right current rating.
Note the 25Vdrop across the 145r inductor.
That tells you the current is ~172mA.
You need at least that rating.
You could replace the inductor with a resistor and the PSU would still work.
adding some capacitance might be a lot cheaper than buying an inductor.
The sch presently shows an rC(L+R)C
You could change that to rCRC, or for more ripple attenuation to rCRCRC.
8uF 500V caps are MUCH cheaper than 7H, or 8H inductors.
r= existing resistance upstream of C13.
C=8uF
In the new
C= 8uF or 10uF, 3off
R= 68r or 75r, 5W or 7W, 2off
Consider an extra resistor before C13 if you increase the capacitance to reduce the load on the valve rectifier, i.e. increase r.
It could be better to stagger the C value.
add 22r (3W, or 5W)upstream of C13. Change C13 to 5uF or 6uF
fit a 68r instead of L1
add an extra capacitor after L1, use 5uF or 6uF
fit a 68r as an extra resistor.
C12 becomes 10uF or 12uF (or two of the previous in parallel
this gives RCRCRC PSU which you can model in PSUD2
and compare to existing sch.
Last edited:
Hello,
Just adding more caps will give your tube rectifier a difficult life. At the time this circuit was developped caps were more expensive than chokes. But i think these people knew what they were doing. If you will replace the choke by a resistor you will reduce filtering because a resistor will give you a 6db filter and a choke will give you 12 db.
Try to find an lc and an rc ripple filter calculatoir online.
Greetings, Eduard
https://www.ampbooks.com/mobile/amplifier-calculators/LC-ripple-filter/calculator/
Just adding more caps will give your tube rectifier a difficult life. At the time this circuit was developped caps were more expensive than chokes. But i think these people knew what they were doing. If you will replace the choke by a resistor you will reduce filtering because a resistor will give you a 6db filter and a choke will give you 12 db.
Try to find an lc and an rc ripple filter calculatoir online.
Greetings, Eduard
https://www.ampbooks.com/mobile/amplifier-calculators/LC-ripple-filter/calculator/
Hello,
Replacing the proposed choke with a 1000 ohm resistor and the second cap with a 40mF one you will have a similar ripple reduction. But of course the choke will sound a lot better because the resistor will make the power supply much slower. It needs to be able to '' charge '' the cap which is '' emptied '' by the circuit so to say
Greetings, Eduard
Replacing the proposed choke with a 1000 ohm resistor and the second cap with a 40mF one you will have a similar ripple reduction. But of course the choke will sound a lot better because the resistor will make the power supply much slower. It needs to be able to '' charge '' the cap which is '' emptied '' by the circuit so to say
Greetings, Eduard
According to a post on this web site.
Eico HF22 Rebuild, Mullard 520 or Williamson? | Audiokarma Home Audio Stereo Discussion Forums
The original Mullard circuit is here.
Twenty-Watt Amplifier
and it uses a 10H, 180mA,200 ohm, Choke.
Other thoughts.
At least no one said a green choke will sound better than a red one.
But why not do yourself a favor and stop wasting time and money on things that glow.
Eico HF22 Rebuild, Mullard 520 or Williamson? | Audiokarma Home Audio Stereo Discussion Forums
The original Mullard circuit is here.
Twenty-Watt Amplifier
and it uses a 10H, 180mA,200 ohm, Choke.
Other thoughts.
At least no one said a green choke will sound better than a red one.
But why not do yourself a favor and stop wasting time and money on things that glow.
MORE HELP please!
Thank you very much everyone!
Was getting frustrated but much happier with your responses: this is my first built and do not want to alter the schematic. Finding a choke with the inductance and current is no problem but I NOT find one with those value at 145 OHMs. Do I have to have it custom built. Is the 145 ohms crucial? Or can I use say 10hy, 200aM and 90 ohms-85ohms 72 ohms which I
can find.
Thank you very much everyone!
Was getting frustrated but much happier with your responses: this is my first built and do not want to alter the schematic. Finding a choke with the inductance and current is no problem but I NOT find one with those value at 145 OHMs. Do I have to have it custom built. Is the 145 ohms crucial? Or can I use say 10hy, 200aM and 90 ohms-85ohms 72 ohms which I
can find.
145 is not important. It determines the amount of heat inside the coil and the final voltage on the last C.
You don't want too much heat, but that is decided by the manufacturer when they give the current rating.
You don't want too much heat, but that is decided by the manufacturer when they give the current rating.
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