Transformer orientation

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petedub
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Transformer orientation

Post by petedub »

Hi
I am rebuilding my amp on a new chassis. I have mounted the PT but am unsure which is the best way for the OT to face.

I have attached a diagram with 2 options, any help would be most welcome,

Thanks, Pete
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JMPGuitars
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Re: Transformer orientation

Post by JMPGuitars »

B is the common standard. You can look through our gallery/archive in the left nav menu for plenty of examples.

Thanks,
Josh
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AussieTim
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Re: Transformer orientation

Post by AussieTim »

Hope you dont mind me jumping in here, I am in the final stages of drilling out my chassis ready to mount all the goodies, my question is is there an optimum known position for the output transformer.
I know about the technique of listening through headphones and moving it around until you find the sweet spot but once I have assembled this beast I do not want to disassemble it again to drill holes and mount the OT
I was thinking of just going with a standard 1974 position but I am happy to accept any advice on better positioning
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petedub
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Re: Transformer orientation

Post by petedub »

Many thanks for the quick reply Josh, I am keen to get this baby up and running, my amp I am rebuilding - which was my first build was the best amp I have ever played through, an original style 18 watter, although it did hum a but hence the rebuild.

I have seen lots of pics that agree with your verdict, the only reason I asked was because a vid on youtube seems to disagree. I have probably misinterpreted something in the video as I am no expert in these matters.
I have included a link to the video, incase you are intersted in shedding some light, but it makes sense to go with common practice.

https://www.youtube.com/watch?v=XUTzfOKxnQs

Thanks again - Pete
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Re: Transformer orientation

Post by JMPGuitars »

That video doesn't show the same transformers that we use. If you're using the 18watt vintage style, then go with B. If you're using a different style of transformer, you might want to test the orientation.

If you're worried about noise and hum, read the soldering and modern ground scheme threads in my signature.

Thanks,
Josh
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petedub
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Re: Transformer orientation

Post by petedub »

Thanks again Josh

I have the 290paz and 1750PA from Hammond.

You have put my mind at rest.

Look out for any other paranoid questions lol.

I watched the you tube vids on soldering that were posted on here (the ones that tell you to turn the projector off!), most informative. I will also be careful to implement the modern grounding scheme, separating the first stages from the power stage.

P.S. Great photo's in the gallery.

Pete
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ViperDoc
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Re: Transformer orientation

Post by ViperDoc »

AussieTim wrote:
Tue 01/18/22 7:21 am
Hope you dont mind me jumping in here, I am in the final stages of drilling out my chassis ready to mount all the goodies, my question is is there an optimum known position for the output transformer.
I know about the technique of listening through headphones and moving it around until you find the sweet spot but once I have assembled this beast I do not want to disassemble it again to drill holes and mount the OT
I was thinking of just going with a standard 1974 position but I am happy to accept any advice on better positioning
I've used the transformer headphone test with great success several times. You can bench test this on a bare chassis without building the amplifier at all.

You will likely place your power transformer in its standard, far-left position (or right for a reverse build). Tape off all secondary PT leads and wire an IEC socket to your PT primary. Make four test leads with spare wire and alligator clips at both ends. Find a favorite pair of over-the-ear headphones and plug the 1/4 inch headphone plug into a stereo Cliff jack. Clip the alligator leads between your headphone jack T and S leads to your OT common and any OT secondary. Then clip another pair of alligator leads between your headphone jack R and S leads and your choke in and out leads. This will place your OT in one ear and your choke in the other.

Make sure your PT is fully taped off, as when you plug it into your wall voltage, your PT will be hot. Plug in your PT and lay it on top of your chassis. Put your headphones on. Place your OT and choke on top of the chassis near the PT and you will hear audible hum in the headphones. As you move and rotate the OT and choke relative to the PT, you will hear the level of hum disappear. Once you have found your desired positions, mark the base of each component with painters tape and markings to help orient the pieces correctly. Snap a phone shot if you want. Now you can locate your mounting holes and adjust your layout and components as required.

One time I found on my Tweed Super build that I got total hum cancellation by rotating my choke and OT in the Z axis (floating sideways), so I mounted them that way on angle aluminum mounts. The amp is dead quiet.

Enjoy.
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