wiring a impedence selector with a 1650K hammond OT

[bastieng]

Anyone ever wired an impedance selector for a 1650K hammond output transformer? You'd think it was simple but if you look at the switching according to the OT design it's not as trivial as I had hoped.

http://www.hammondmfg.com/1608.htm

 

[GeorgK]

IMHO the third schematic contains a mistake - guess the speaker should be connected between blk and yel.

 

[GeorgK]

Addendum

The Transformer has 3 x 4Ohms windings. 4 Ohm operation wires 2 of them in parallel, 8 Ohm adds another 4 Ohm winding. So switching between these two is simple.
peace,
georg

 

[bastieng]

I have a simple rotary switch. My confusion centers around how you set up the switching of the other wires.

 

[GeorgK]

Switching between 4/8/16 Ohms using that switch is not possible. What you can do anyway is switch between 4 and 8 Ohms using [blk] as common ground and [gm/yel] for 4 Ohms / [yel] for 8 Ohms load respectively. Comparing these two configurations you see that the rest of the wiring (i.e. the two parallel windings) are identical. If 16 Ohms load is not that important you're done. Anyway, you still can connect a 16 Ohm cabinet to the 8 Ohm tap if you don't mind a slight loss in output power.

 

[oldfatbubba]

A solution is available through Antique Electronics Supply...

http://www.tubesandmore.com/scripts...levclients/cemirror/ELEVATOR.FXP?item=P-H1600

Draw NFB from the green wire and adjust the value of the feedback resistor for a 4 ohm load. If the circuit calls for 56k feedback resisor when the loop connected to the 8 ohm tap, divide by 56K / 1.41 = about 40K (39K is close enough). You may adjust further downward if needed.

Bubba