# Transformer/chassis layout questions



## greco (Jul 15, 2007)

I bought a small head cab (with chassis) from Ripper for my Champ clone build that is taking me several decades (j/k ...but years for sure) to complete. 

I'm wondering if there is any preferred locations on the chassis for the transformers. I know that the laminations must be at 90 degrees to each other. I am considering putting the power transformer at one end (near the power cord, fuse, pilot light and switch) ...and the output transformer at the other. This gives me plenty of room in between for the board and tubes. 

I have looked at pictures of several layouts of DIY champ builds (on the internet) and they vary significantly as to the choice of location for the transformers.

Is it better in any way to have them closer together?
(or further apart ?)

If I end up with some longer wire runs (by putting them at opposite ends of the chassis), will I be at more risk for hum and other unexpected problems?

All comments/suggestions are welcomed.

Thanks

Dave


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## Gunny (Feb 21, 2006)

The further apart the two transformers are, the less change of magnetic interactions. Remember, the OT only handles high voltage DC and the amplified signal (no 120 Vac). Therefore, the distance between the transformers should not cause any problematic issues because the lengths of B+ wiring should be immune from most sources of interference (the use of 'should be' is my disclaimer 'cos there's bound to be someone who would argue that nothing is totally free from interference).


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## greco (Jul 15, 2007)

Humble bump...hoping for a few more comments.

Thanks

Dave


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## keeperofthegood (Apr 30, 2008)

Well... only a personal point of view and nothing whatever to or against one layout or another. I have the pet peeve of picking up any equipment and having one side significantly heavier than the other. I would suggest that no matter where you place the heavy parts (the transformers do have some mass) that you try to do so in a balanced manner or means that it could be made balanced.

:wave: Just my wrenched shoulders having a small voice in your build ideas.


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## RIFF WRATH (Jan 22, 2007)

forgot to check out my champ clone last night....dang........just recieved my deluxe clone chasis this morning (thanks Wild Bill, you are the best)......there are 4 tubes on the left hand side of the chassis deck........the small power transformer is in the middle with 2 more tubes and the heavy output transformer is on the right hand side of the deck..... hope this helps......


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## Wild Bill (May 3, 2006)

Over the years I have seen trannies placed all over the chassis! Amps from the 30's and 40's seemed to be wilder than by the 50's. I think that's about the time the industry had learned how to "keep out of trouble".

Riff's amp has the trannies in those positions only because that's the way the amp was made and I didn't bother to change it. The original designer had gotten away with it so why not?

However, there are some general rules. The idea of balancing the weight is a good one, especially since this usually means putting the power and the output tranny as far apart as possible on each end of the chassis.

It's also true that it's best to have the cores of each trannie at 90 degrees to one another. This minimizes any hum coupling between them. On some hifi amps the designer would actually drill only one mounting hole on the output transformer so he could rotate it a bit from exactly 90 degrees. If you put voltage into the power transformer and a pair of headphones on the output transformer you can actually hear any induced hum. The nature of making transformers means that things rarely are exactly symmetrical. Often he'd find that a few degrees either way hit the "sweet spot" or the absolutely least amount of hum pickup.

It also makes sense to follow the Marshall layout, where the input jacks are at the front and the power trannie at the back. The circuit flows across to end up with the power tubes and the output trannie on the other side of the chassis.

Don't worry about running the centretap/B+ wire from the output trannies primary back to the power supply. DC doesn't radiate from a wire, so powering the plates of the tubes is not a problem. As far as the output AC signal, remember that these wires should end up rather short to the plates of the output tubes, which should have been placed near the output trannie. Besides, they are relatively low impedance, being at the primary load of the OT which is 3400 ohms, 6600 ohms or similar. Hum radiation or pickup is highest with higher impedances. Grid inputs are in the hundreds of thousands of ohms, or more. Plate loads are far lower.

I worked on an amp that came with an extension speaker for a 16mm projector. The amp was mounted in the base of the projector and a cable ran about 40 feet to the extension speaker cabinet. The OT was NOT in the amp! It was mounted on the speaker! The plates of a pair of 6V6's fed into 40 feet of UNSHIELDED cable and the design worked perfectly, with no hum pickup at all. Again, it was because the load to the primary of the OT was only a few thousand ohms. Leslie speakers with Hammond organs run 10k signal loads from the organ to the amplifier and work fine, for the same reason.

:food-smiley-004:


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## Wild Bill (May 3, 2006)

RIFF WRATH said:


> forgot to check out my champ clone last night....dang........just recieved my deluxe clone chasis this morning (thanks Wild Bill, you are the best)......there are 4 tubes on the left hand side of the chassis deck........the small power transformer is in the middle with 2 more tubes and the heavy output transformer is on the right hand side of the deck..... hope this helps......


Glad you're happy, Gerry! Let me know how those Muddy Waters licks are sounding!

:food-smiley-004:


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## RIFF WRATH (Jan 22, 2007)

sorry to high jack your thread a bit Greco.........Wild Bill........I was going to wait to try it out until I got it installed into a cabinet, which I probably will have to build........I guess I'm a big chicken....lol........can't wait to try it.....


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## greco (Jul 15, 2007)

RIFF WRATH said:


> sorry to high jack your thread a bit Greco.........*Wild Bill..*......I was going to wait to try it out until I got it installed into a cabinet, which I probably will have to build........I guess I'm a big chicken....lol........can't wait to try it.....


No problem Riff. I just hope that Wild Bill sees this post.


Many thanks to all that responded.....very much appreciated. :bow:

Cheers

Dave


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