Lundahl Transformer
Manufacturer of  Ultra High Quality Audio Transformers
    Introduction (the Part number below, is the same as in the pricelist
  Tube Power Supply Chokes
Part14..21
   Tube Output transformers
Part 2
   Filament Chokes / High Current Chokes
Part 22
   Tube Mains transformers with DC cancellation
Part 3
   Plate (anode)  Chokes
Part 23
   Mains Cleaning transformers with DC cancellation
Part 4
   Grid Choke
Part 24
   Transformer Covers (Housings)
Part 5
   Interstage
Part 25
   Various transformers, not mentioned here
Part 6
   Signal Input      
Part 7
   Signal Output      
Part 9
   Moving Coil      
Part 10
   Guitar Input
Tech1
   (technical info) PPZ transformers
Part 11
  

Microphone
Tech2
   (technical info) Product Storage
Part 12
   For Digital Audio. Finest Quality
Tech3
   (technical info) Amorph Cores
Part 13
   Interconnect Solutions
Tech4
   (technical info) DATASHEET DOWNLOAD

 

Lundahl Power Supply Chokes

Introduction

All Lundahl products are based on their double coil (symmetrical) C-Core technology. Also the chokes. This means you have always two coils available. These you can wire in three ways:

  1. in Series. This is how the Henry value is specified. If you buy a 10H choke, it will have 10H with both coils in series.
  2. in Parallel . This option has only 50% of the inductance, but for that you have twice the current and half the DC resistance. The best thing to do is, check the price list of jacmusic.com because in there is a compact overview of what is the best coil for a required DC current. Most if the time series connection gives the best value for money, but with some
  3. in Common Mode Rejection configuration.  In this configuration, one coil is in the positive lead to the second capacitor, and one on the ground lead to the second capacitor.  This will give lowest field radiation coming from the choke.  Such good results can not be achieved with lower cost E-Core chokes, and the Lundahl double coil chokes are a major step into the direction of a really hum-free amplifier.  Electrically this is calculated as a series connection. More information also here below.

NOTE: for For small power supplies with very low hum requirements, such as in pre-amps, you can use plate chokes like LL1667/25 as power supply chokes, they are qualified for this use as well. In the table (below) you see some of the plate chokes listed. You will get extremely high inductance that way. This allow you to work with less big capacitors, and in that way reduce capacitor charge peaks which are responsible for hum radiation. The relatively high DC resistance will however give not much voltage drop, since you work are low current. Even the DC resistance is good, since it is an additional stabilizer element, and also it is helpfully at start up when capacitors are still empty. Then again with higher current versions such as 50mA and more, you will see the DC resistance gets lower. All together the below table shows a very harmonic family of products.

 

 
You must connect
Resistance
mA
Henry
Both coils in Series
2400
10
400
Both coils in Series
2400
15
270
Both coils in Parallel
300
20
200
Both coils in Parallel
300
30
135
Both coils in Series
680
25
100
Both coils in Parallel
170
50
25
Both coils in Series
60
100
20
Both coils in Series
130
100
17
Both coils in Series

130
130
13
Both coils in Series
60
140
15
Both coils in Series
36
160
10
Both coils in Series
60
200
10
Both coils in Series
36
200
8
Both coils in Parallel
15
280
3,75
Both coils in Parallel
33
320
2,5
Both coils in Series
36
400
4
Both coils in Parallel
9
800
1

Just pick the current you need from this table, and choose the right Choke.

 In the double coil configuration, one coil is in the positive lead to the second capacitor, and one on the ground lead to the second capacitor.  This will give lowest field radiation coming from the choke.  Such good results can not be achieved with lower cost E-Core chokes, and the Lundahl double coil chokes are a major step into the direction of a really hum-free amplifier.   The data sheets gives a good diagram of how  to connect a double coil choke, using it's full features and get best noise rejection from it. (check for instance here, all at the bottom of the last page). Of course, it is still possible to use them as a single coil also. 

Overview of types

1 ) LL1638 Wound with thick wire.  Gives best performance for  High Current applications. Available with different air gaps, which results in different current / henry. 
2)  LL1673 Same as above, but wound with thin wire.  Gives best performance for  High Henry applications. 
3) LL1685 Same as 1673, but wound on the next smaller core.  Lower in price, but less Henry.
Note: At "medium"  current,  many combinations can be made, but some chokes will perform better than others.  In the  following table, the best combinations are given, with the most Henry for the money, at a several currents. 

 

SOME DESIGN RULES FOR A HUM-FREE TUBE RECTIFIER CIRCUIT


Standard circuit diagram, with well defined earth point.

In this circuit diagram  the primary Capacitor is C1, the secondary Capacitor is C2.

 

Standard circuit diagram, with improved Common Mode rejection.

In this circuit diagram  the primary Capacitor is C1, the secondary Capacitor is C2.

Emission Labs Application Note about improved CMR Coil connection - CLICK HERE

With High Voltage power supplies,  the best results are always coming from a large choke.  This has many times more effect than using large capacitors.

  1. The BIG misunderstanding from people that made low voltage power supplies before. Here, using BIG capacitors,  like 10.000...50.000uF will improve the result, because with Low Voltage designs,  the energy storage is only in the primary capacitor.    Not so with tube rectifiers!  These are high impedance, and  the energy storage is mainly in the choke.  With tube rectification,  you need to take the a small primary capacitor. (see also the next note).   There  is a maximum value for that in the tube data sheet.  It is for instance 4uF for the 274A. The maximum is the highest value, and you should feel free to take a lower value also.  The  higher the  value, the larger the charge current through the primary capacitor.  The wires will radiate an AC magnetic field, and this gives hum into the pre-amp. (and you'll never find where this hum is coming from. The path is through air....)
  2. Some applications leave the primary capacitor completely away, and use only the energy storage in the choke.  This will improve the efficiency of the power supply, and gives more current.  This is a  method, not recommended with low cost chokes,  because it will  make the plate choke hum (mechanically). With the LUNDAHL chokes this is possible, and no hum will result from it.
  3. Push pull amplifiers are very insensitive to power supply hum.  They can work completely without hum, even with 30Volt AC on the DC voltage, but.... only as long as the rest of the construction is well done.
  4. SE amplifiers are very sensitive, but  if there are any hum problems it is normally not the power supply.  Improving the power supply first capacitors can will help,  because it reduces all AC voltages in the whole amplifier. Still you are curing the problem at the wrong place, and never get a full cure because of that.  More often it is bad wiring, or some other mistakes somewhere. The recommended capacitor values in the circuit diagrams are normally more than enough.
  5. With Mercury rectifiers  people often say they "hum", or sound in some way "unquiet".  That is true,  but it comes from bad designs. Good designs do not hum at all.  These rectifiers have an "ignition" before they get in the conductive state. Because of that,  they have a lower internal impedance, and can work with surprisingly large primary capacitors.  But... this is the industry method, and not what we want for HiFi.  Again.... what these rectifiers show in their data sheets are maximum capacitor values for industry applications, and  no "must use"  values for HiFi!   Take the same low primary capacitor value as for non-mercury rectifiers, and you will have no hum.
  6. Here is the final conclusion:  If you want to oversize the power supply,  the best effect comes from:

    7. a) The CHOKE
    b) The SECONDARY Capacitor
    c) there is no c;)
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    (Last updated: 02-Jan-2012 14:05 )