# Hammond transformer questions

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#### funk1980

I've got some very basic question about Hammond transformers. Both power and output. My next project is going to be my first venture into tube power amps, so I've never worked with output transformers. Hammonds are easilly available, so 'm going to use those (1650 series). I don't get (and I'm sure it's very basic) the primary impedance rating. The 1650T states 1900 ohms C.T. Does this simply mean it's center tapped and anode to anode impedance is 1900 ohms, or does it have an impedance of 1900 ohms from the center tap to each anode connection, so 3800 ohms in total?

Same goes for hammond power transformers (e.g. 700 series). It states 750V C.T. Does that mean 750-CT-750 or 375-CT-375 (750 total).

I'm sure it's basic stuff, but very confusing for someone who's never workes with these power amp components. Thank!

#### Ketje

If you have 750V with a center tap then it's just that.A 750V winding with a CT ,the CT is then at 750V/2.
The UPT is somewath more complicated.Yes 1900 ohm CT is totaly 1900 ohm but the CT is not at 2x 950 ohm.It is 2x (1900/4).
In a PP the tube "sees" 950 ohm as long as they operate in classA,the other side "helps".With larger signals,classB situation the charge dubbles (halve impedance).
The same thing on the secundairy,if you have 0,4,8,16 ohm the 4 ohm is the center,not the 8 ohm.
Mona

#### funk1980

Thanks! So the C.T. is just to dictate there's a center tap present. Got it.
The whole class a vs. class b vs. class ab and the resulting change in impedance is still a bit confusing to me, comming from preamp triodes . But I'm learning as I go.

#### Tom Bavis

Think of it this way:

Class A SE: a handsaw
Class A P-P - two man saw (both ends pushing and pulling)
Class B P-P - two man saw, pulling alternately.
Class C RF amp - pushing a swing for part of a cycle - tuned circuit fills in the rest of the cycle.

#### GoatGuy

Think of it this way:

Class A SE: a handsaw
Class A P-P - two man saw (both ends pushing and pulling)
Class B P-P - two man saw, pulling alternately.
Class C RF amp - pushing a swing for part of a cycle - tuned circuit fills in the rest of the cycle.

Class D "digital" amp - sitting on a swing with a huge machine gun, popping it for and aft at various speeds to effect motion.

GoatGuy

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