Hammond S6 Chord organ OT ?

[mresistor]

I've got a Hammond S6 OT and was looking at the Chord Organ schematic and the OT appears to have a center tapped secondary.  Why would they do this? And I was going to use it to build a 5F10 Harvard amp,  The 3 secondary colors are black green and yellow.


Black to green is .5 ohms
Black to yellow is .4 ohms
Yellow to green is .7 ohms     using a Fluke


Anyone have any knowlege and advice on how to proceed?  I was thinking I guess I'd make yellow or green the grounded lead and the other the hot lead and tape off the black.  But then what would the reflected impedance be?   double what it was with the center tap?

[HotBluePlates]

... the Chord Organ schematic ... the OT appears to have a center tapped secondary.  ...

Looks like they needed the full winding to drive the speaker.

However, there is feedback taken from one end of the winding.  You can bet wherever that goes, the circuit is referenced to ground.  So the center-tap means the feedback loop is fed half of the voltage sent to the speaker, rather than all of it.

Is that worth doing instead of just using a larger series resistor in the feedback loop?  I dunno, since we only see part of the circuit in the fragment you posted.

... I've got a Hammond S6 OT ... I was going to use it to build a 5F10 Harvard amp ...

Is the stock Hammond speaker 8Ω like the Harvard?  If so, ignore the center-tap & don't use it.  Use the outer ends of the secondary for your speaker connections.

[mresistor]

Oh sorry here you can see the feedback couples back to the grid pin 3 of V27. 


There were 2 10" speakers in the organ and they are long gone.. I don't remember what the ohmage was but would guess they were 8 ohms in parallel.

[Stuff4bikes]

Not sure if this is any help but I have this transformer in a push pull stout. I just folded the yellow wire and heat shrinked it.

[mresistor]

this transformer in a push pull stout.

Hi Stuff..   are you saying you are using an S6 OT?  An AO-20936-2? 


I have used this one I have a couple of times to t-shoot amps like a Blues Jr that had a fried OT, using the substitution technique, and the OT sounded great.  I too used the black to ground and the green as the hot lead. It's the schematic and my meter readings of it that cause me to wonder about how this OT was used.

[mresistor]

Here's a different config of an S6 power amp that is relevant to the organ I had which had two speakers. Definitely some differences in the feedback loop and surrounding components and where the phono is input, or it's just drawn differently.

[HotBluePlates]

... wonder about how this OT was used.

I would apply a small (6-7v AC?) voltage to the primary, and measure the resulting voltage from Green to Yellow (your highest resistance secondary).  Then do the math to calculate the Impedance Ratio & primary impedance if you connect your 8Ω speaker to those wires.

[sluckey]

... wonder about how this OT was used.

I would apply a small (6-7v AC?) voltage to the primary, and measure the resulting voltage from Green to Yellow (your highest resistance secondary).  Then do the math to calculate the Impedance Ratio & primary impedance if you connect your 8Ω speaker to those wires.

I would rather use about 30V to 50V. That will give you an easier to measure secondary voltage. For example, assume the OT has a 30:1 voltage ratio. Putting 6 volts on the primary will give only .2v on secondary, but 30v would give 1v on the secondary.

[Stuff4bikes]

this transformer in a push pull stout.

Hi Stuff..   are you saying you are using an S6 OT? 

I am not, just one with the extra output wire and similarly colored scheme.

[mresistor]

Thanks HPB and Sluckey ..   I was trying putting 10vac on secondary and metering primary and  WOW!!!   it was over 900vac or at least that's what the meter was reading, shut that puppy down quick.



I'll be trying the VAC on primary measure secondary method this afternoon.   Got the board layed out, drilled turrets installed and now...  isn't it beer time?    

[shooter]

isn't it beer time?

I was trying putting 10vac on secondary

it was over 900vac

AFTER, you unplug your toys 

[mresistor]

Shooter for some reason my mind was thinking "PT"  ..   

[shooter]

Uh hu.... it was thinking beer and got distracted 

[mresistor]

OK  I tested this OT      30v applied to brown and blue


Black - Grn  =  .199
Yellow - Grn =  .196
Yellow to Blk = .307


It appears like this is not a suitable OT   I'm getting way high turns ratios      yet  this was in the S6 using 2 6V6 PP

[PRR]

> Black - Grn  =  .199
Yellow - Grn =  .196
Yellow to Blk = .307

That does not add up.

A single-core (not 3-phase etc) transformer, the taps on each winding must add-up like measuring the length of a football field. If you gave me these numbers

199 feet west end to center
196 feet east end to center
307 feet end to end

...well, is it 395 feet or 307 feet?