**Lundahl Guidelines **

Guideline for use of Lundahl output transformers

This is also to answer the most FAQ , and to help understand how to obtain
the best possible

Results from the outputtransformer

Impedance ratio apply for SE & PP

You can use double the rating of primary current at the cost of primary inductance
,

2 primary windings in series and then parallel , this reduces inductance by
1/4 and doubles

primary current .

Also note when you get very low ratios that the internal wire resistance is
going to be a big loss factor

And this should be checked for

For SE try to use the lowest number possible for your application , to get
the best bass response

Offcourse this will reduce slightly the high frequency response

Basic Frequency response : 7Hz to 25kHz within 0,5 dB and 2Hz-75kHz within
6dB

Fase shift : 20kHz 13,5 ° and 2,2µs group delay

**3 basic models :**

---------------------LL1620 ------------LL1623-------------- LL1627

Each primary winding

Has a turn ratio = ---19,2 -----------------13,4------------------- 8,5

Primary winding DC resistance

---------------------77ohm ----------------41 ohm ---------------14 ohm

Each secondary winding

Has a turn ratio = ----1 ----------------------1--------------------- 1

Secondary winding DC resistance 0,4 ohm ---0,4------------------- 0,4

All transformers have 4 primary coils and 8 secondary coils

The max voltage across

Primary windings (all in series)

-------------PP=860v SE=380v ----PP=610vSE=270v----- PP=380v SE=170v

**Formulas : **

X = impedance ratio

N1 = primary turn ratio

N2 = secondary turn ratio

X= N1 * N1 / N2 * N2

Primary impedance or plate load=secondary impedance or speakerload * impedance ratio( X )

Also keep in mind that I am only studying 8 ohm connection but if you hook
up 4ohms

As secondary load then the primary plate load is halved as well , but if you
have 16 ohm load

Then plate load will double (compared to 8 ohm )

**Lets study some possibilities :**

**Case 1 :**

All primaries in series N1 = for each model ( primary turn ratio )

LL1620 = 19,2 * 4 = 76,8

LL1623= 13,4 * 4 = 53,6

LL1627= 8,5 * 4 = 34

**Option 1** = all secondaries parallel so N2 = 1

For 8 ohm speaker the anode load will be :

LL1620 = 5898 * 8 = 47 k ( k = kilo ohm)

LL1623 = 2873 * 8 = 23 k

LL1627 = 1156 * 8 = 9,2 k

**Option 2 **= 2 secondaries in series and then the 4 groups parallel to
each other N2=2

For 8 ohm speaker the anode load will be :

LL1620 = 1474 * 8 = 11,8 k ( k = kilo ohm)

LL1623 = 718 * 8 = 5,6 k

LL1627 = 289 * 8 = 2,3 k

**Option 3**= see alt C ( 2 secondaries in series and then in series with
2 secondaries parallel and this parallel to

The other secondary with identical scenario ) N2=3

For 8 ohm speaker the anode load will be :

LL1620 = 655* 8 = 5,24 k ( k = kilo ohm)

LL1623 = 319 * 8 = 2,55 k

LL1627 = 128 * 8 = 1 k

**Option 4** = 4 secondaries in series and then parallel to each other N2=4

For 8 ohm speaker the anode load will be :

LL1620 = 368 * 8 = 2,95 k

LL1623 = 179 * 8 = 1,45 k

LL1627 = 72 * 8 = 576 ohm

**Option 5** = 8 secondaries in series N2=8

For 8 ohm speaker the anode load will be :

LL1620 = 92 * 8 = 736 ohm

LL1623 = 45 * 8 = 360 ohm

LL1627 = 18 * 8 = 144 ohm

______________________________________________________________________________

**Case 2 :**

2 primaries in series and then parallel to each other N1 = for each model

(this will double the primary current rating and divide by 4 primary inductance
= worse LF response )

LL1620 = 19,2 * 2 = 38,4

LL1623= 13,4 * 2 = 26,8

LL1627= 8,5 * 2 = 17

**Option 1** = all secondaries parallel so N2 = 1

For 8 ohm speaker the anode load will be :

LL1620 = 1474 * 8 = 11,8 k ( k = kilo ohm)

LL1623 = 718 * 8 = 5,6 k

LL1627 = 289 * 8 = 2,3 k

**Option 2** = 2 secondaries in series and then parallel to each other N2=2

For 8 ohm speaker the anode load will be :

LL1620 = 368 * 8 = 2,95 k

LL1623 = 179 * 8 = 1,4 k

LL1627 = 72 * 8 = 576 ohm

**Option 3** = 4 secondaries in series and then parallel to each other N2=4

For 8 ohm speaker the anode load will be :

LL1620 = 92 * 8 = 736 ohm

LL1623 = 45 * 8 = 360 ohm

LL1627 = 18 * 8 = 144 ohm

**Option 4** = 8 secondaries in series N2=8

For 8 ohm speaker the anode load will be :

LL1620 = 23 * 8 = 184 ohm

LL1623 = 11,2 * 8 = 90 ohm

LL1627 = 4,5 * 8 = 36 ohm

**Case 3 :**

all primaries parallel to each other N1 = for each model

gives you 4 times primary current rating and divides by 16 inductance , can
be used with very low impedance tubes

or mosfets or transistors.(beeeuuuurk )

LL1620 = 19,2 * 1 = 19,2

LL1623= 13,4 * 1 = 13,4

LL1627= 8,5 * 1 = 8,5

**Option 1** = all secondaries parallel so N2 = 1

For 8 ohm speaker the anode load will be :

LL1620 = 368 * 8 = 2,95 k

LL1623 = 179 * 8 = 1,4 k

LL1627 = 72 * 8 = 576 ohm

**Option 2** = 2 secondaries in series and then parallel to each other N2=2

For 8 ohm speaker the anode load will be :

LL1620 = 92 * 8 = 736 ohm

LL1623 = 45 * 8 = 360 ohm

LL1627 = 18 * 8 = 144 ohm

Option 3 = 4 secondaries in series and then parallel to each other N2=4

For 8 ohm speaker the anode load will be :

LL1620 = 23 * 8 = 184 ohm

LL1623 = 11,2 * 8 = 90 ohm

LL1627 = 4,5 * 8 = 36 ohm

**Option 4** = 8 secondaries in series N2=8

For 8 ohm speaker the anode load will be :

LL1620 = 5,75 * 8 =46 ohm

LL1623 = 2,79 * 8 = 22 ohm

LL1627 = 1,12 * 8 = 9 ohm

**Study of 3 connection alternatives as suggested by the datasheet**

Model LL1623 connection alternative B = 5600ohm to 8 ohm load

All primaries in series = 53,6 turn ratio = 2873

Secondaries :

here we have 2 groups of 4 windings parallel , each supplying one speaker terminal

1 group supplying the negative terminal has all its positives together

2 nd group has its negatives together and connected to the positive of group
1

this gives a turn ratio of 2 = 4

or for 8 ohm load : 2873/4*8=5746 ohm + dc resistance of coils (164 ohms )

_______________________________________

same model alternative C = 3000 ohm to 8 ohm

All primaries in series = 53,6 turn ratio = 2873

Secondaries :

here we have 2 groups in parallel ,

both identical = 2 windings in series and then in series ( 2 windings parallel
)

this gives a turn ratio of 3 = 9

or for 8 ohm load : 2873/9*8=2553 ohm + dc resistance of coils (164 ohms )

________________________________________

same model alternative D = 1600 ohm to 8 ohm

All primaries in series = 53,6 turn ratio = 2873

Secondaries :

here we have 2 groups in parallel ,

each group = 4 windings in series

this gives a turn ratio of 4 = 16

or for 8 ohm load : 2873/16*8=1436 ohm + dc resistance of coils (164 ohms )

**Small note on LL1663 & LL1664 :**

The former has a ratio of 4+8 + 4+8 to 1

So the following connections are possible :

4 to 1 = not recommended

12 to 1 , ( double I dc inductance /4 ) = 144 * 8 = 1200 ohm primary

( can be obtained also with only one coil instead of 2 coils in parallel )

12+4 to 1 = 256 * 8 = 2 K

12+8 to 1 = 400 * 8 = 3,2K

12+12 to1 = 576 * 8 = 4,6K

the LL1664 :

9,6 + 9,6 to 1 = 368 * 8 = 3 K

what is missing here are a few inductance measurements

but excellent transformer for low power applications , because the high frequency
response is astounding

and if not using lots of current then inductance is more then high enough for
good low frequency response

**If in doubt of the primary impedance of a transformer , **

You have 2 simple (almost identical ) methods of measurement ,

Step 1 : disconnect speaker & shut amp off ( discharge capacitors )

Step 2 : hook a 6 volt ac transformer (50 or 60Hz)on secondary side = instead
of speaker

Step 3 : measure ac voltage secondary =U2

Step 4 : measure primary voltage (be carefull high voltage ) = U1

Step 5 : divide voltages step4/step3 = ratio n = U1/U2

Zprimary = Z secondary * square ratio n

The other method consist in using a frequency generator and a scope , and doing exactly the same

**Final Conclusion :**

There are still lots of possibilities on how to connect these trannies , like only using 3 primaries in series and not connecting the 4 winding , and on the secondary side , you could just use one winding and not connect the 7 others .

So this is truly a very high quality universal transformer , that requires a good understanding of how to play with it , I think it is best if you use all the windings and especially all primaries in series.

If you have any comments ( positive ones will be treated first) ,

please share by email,as I am always eager to learn more

sales@diyparadiso.com

Benny Glass

for info email me at sales@diyparadiso.com