Transformer question

[dhuebert]

I have a question about transformer orientation. If I remember correctly the E-M field around an E-I transformer describes a torus roughly with the plane of the torus parallel to the laminations. If I orient the transformer so output tubes are within the field, will there be a problem with feedback?

don

[erichayes]

Hi All,

Never say never, Don, but in my first prototypes of the 1773 I tried every conceivable combination of transformer to transformer and transformer to tube configuration and proximity. Apparently the EM field is more M than E, because the tubes didn't give a damn where the transformers were or how they were oriented, but the trannies coupled quite nicely, thank you, when they were within a couple of inches of each other and the laminations were in line.

[EWBrown]

IIRC the low frequency EM fields will extend out further from the trannies, than will the higher freqs. 50/60Hz can and will couple quite "nicely", not only from the power trannie, but from the filter choke(s) as well, to the OPTs. The best approach is to keep the core axes of the PTs, OPTs and chokes all at mutual 90 degree "orthogonal" orientation, as done in the ST70, for example.

The tubes themselves aren't really very magnetic-field sensitive, at least it's not going to be a problem in most normal amplifier designs.
It's still a good practice to keep the low level, preamp and driver stages as far from the power tannie as physically possible.
There is more of a concern for heat radiating from the power tubes (and rectifier) affecting the transformers than about any possible H-field (magnetic) coupling.

HTH

/ed B in NH

[dhuebert]

Thanks guys.

I wonder if the field is rather weak, requiring two interacting fields to produce an effect.

Of course we know that magnetic fields have a strong effect on electrons and we know that electrons are travelling through space from the cathode to anode so I wondered if the transformer might "deflect" some of those electrons. We have to keep in mind that the plate might act as a shield having that big B+ on it.

The reason I ask is that I am building a bass amp. The chassis will be about 20 inches long with the trannys at opposite ends. I can save an inch of length if I orient them parallel to each other but then the laminations of the output tranny are pointing right at the output tubes. What I get from you is: No Problem.

Don

BTW I wish you guys would go to "guitar amps" and answer my question about tube rectifiers.