# Hammond 1750n OT



## copperhead (May 24, 2006)

A quick question on the wiring on the primary side of this Tranny . is the Red wire the center tap ? 
http://www.hammondmfg.com/pdf/EDB1750N.pdf


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## epis (Feb 25, 2012)

No, white is centre tap.


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## copperhead (May 24, 2006)

Thank you epis ,I had no internet out in the garage & my phone would net let me open the pdf . 
I have this OT wired in my new 2204 build & the amp is complete but no sound .Not sure if the output transformer is related to my no sound problem but I think the signal is getting push to ground ' not any sound at all ,on hiss or hum . & both terminals of the jack test grounded 
i couldn't source an impedance selector when ordering the parts so I figured i would just add 4,8,16 ohm cliffjacks on the back .Any one got a diagram of how the wire ?


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## epis (Feb 25, 2012)

No problem, you don't really need a diagram, just use 3 dedicated jacks for 4, 8 and 16 Ohms, run black wire to ground lugs on all three jacks and do not solder ground (black) to switch lugs.


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## copperhead (May 24, 2006)

That's what I tried , the dedicated wires 4,8 & 16 ohm to the tip of each cliff jack soldered all the way across the 2 connections & the common soldered to the sleave legs of the cliffjack & soldered to ground & the tip for some reason is showing continuity to ground .


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## epis (Feb 25, 2012)

Just to make it clear, check out image in the link :
Amp Maker: Guitar amp kits and parts :: Jack plugs and sockets :: JTM-type jack socket
You should wire points 3 and 4 on all the jacks to ground and black wire from OT.
Solder 4,8,16 Ohm wires to points 1. ( or 1 and 2, it's not gonna hurt anything)
After soldered you can't really measure resistance from the jack tip, it will show as continuity toward ground, but actually you'll measure resistance of secondary windings of OT.

P.S.
If you had speaker output shorted to ground, when you strum the strings on the guitar you would hear a faint sound noise (buzz) from your output transformer as well.


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## copperhead (May 24, 2006)

I've bypassed the jack using alligator clips going to the speaker cable & no difference .
I've noticed when i ground the common wire of the OT the 16 ohm wire shows continuity to ground as well ,I'm wondering if this is normal ?


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## epis (Feb 25, 2012)

It is normal, all 3 secondary windings are in series, it is not really continuity to the ground, actually very low resistance.
You need to troubleshoot output stage, check out your grounds,high voltages and bias. Cheers, Damir

P.S.

Check that "continuity" with your multimeter in Ohms setting, just to be sure. Everything I try to help you is just guessing, I even don't know if everything is wired properly.


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## nonreverb (Sep 19, 2006)

I'd be looking at your B+ on the plates and screen pins. Then the PI plates. If any of these voltages are not present, you won't hear a thing.
Do you have gut shot so we can see what's going on in there?


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## WCGill (Mar 27, 2009)

Output tube cathodes grounded? Screen B+ present?


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## copperhead (May 24, 2006)

epis said:


> No problem, you don't really need a diagram, just use 3 dedicated jacks for 4, 8 and 16 Ohms, run black wire to ground lugs on all three jacks and do not solder ground (black) to switch lugs.


 Thanks , got it figured out but I am getting some oscillation from this negitive feed back wire 
,what should i do with the negative feed back ? I mainly use 16 ohm or 8 ohm


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## WCGill (Mar 27, 2009)

Oscillation? If the feedback causes oscillation, the plate leads may need to be reversed.


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## epis (Feb 25, 2012)

WCGill said:


> Oscillation? If the feedback causes oscillation, the plate leads may need to be reversed.


Yep, you're getting positive feedback instead of negative.


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## copperhead (May 24, 2006)

Yes as soon as i posted the problem about the feedback , i remembered i may have to reverse the primary's for this reason , reversed the leads & it took care of it .


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