Transformer practical design questions

[Walter66]

Hello,
wanting to use the CineMag S217D replica in a tube preamp, there is no data given for the shielding of the unit. Original S217D provided 50dB of shielding but maybe they have changed the housing?
Tertiary winding will be grounded for electrostatic shield. Can this replica be placed right next to an electron power tube or will the tube induce hum into the transformer?
There are another two, fully MIL case shielded, audio transformers included in the design. One has 95dB of shielding, the other is unknown.
Do all those transformers have to be put far away from electron tubes or isn't it critical in respect of hum inducing? First stage is MM phono input stage. Thank you.

 

[Walter66]

Bump. Nobody can give advise wether electron tubes are sensitive to audio transformers vice versa?
Do they have to be placed far away from transformers or can they penetrate transformer performance when placed too close?
I think audio gear designers should treat this question as relevant, so please give advise on this topic.
When I put a big tube like 807 right next to a shielded audio signal transformer, will it lead to problems?
What degree of dB shielding is necessary to have them stand together without causing problems?

 

[ruffrecords]

As a rule transformers are not sensitive to nearby tubes and vice versa. What transformers are sensitive to is magnetic interference from other transformers. Often the signal level in an output transformer is high enough that no special precautions are needed. Sensitive input transformers on the other hand do need excellent magnetic screening as well as siting well away from other transformers (especially power transformers).

Cheers

Ian

 

[CJ]

Fender tilts their reverb transformers at 45 degrees to prevent oscillation.

The reverb tubes are in close proximity to the reverb transformer.

Those f/b winds on the 217 xfmr are located between the Pri and Sec so they will cut down on capacitance but do nothing about stray fields.

The nickel core of the xfmr is better at pulling in stray fields than silicon steel so you need to be a bit more careful about placement.

 

[Walter66]

Thanks, much relevant for placing the transformers. PSU is an electrostatic and electromagnetic shielded toroid which sits in a separate chamber of steel enclosure. The problem that may induce additional hum could be an output-input loop to and from the external LCR- RIAA network via 600 Ohm XLR via input/ output transformers. Will see how this works out.

 

[john12ax7]

If possible leave yourself the option of rotating the transformer before it gets permanently mounted. There is usually a sweet spot in the rotation to minimize any problems.

 

[CJ]

And maybe use a plastic lid on the enclosure, many people build quiet stuff only to have it become noisy after they bolt the lid on..

Kind of like putting an I bar on an E lam, thus completing the flux loop.

Ever wonder why reverb pans have no bottom?

If you don't believe me try putting a sheet metal plate on a reverb pan like idiot me.

 

[Walter66]

Could the phono out (big) and input (small) transformers placed side by side? Small one has 95dB of triple shielding, big one unknown.
Or should there be some space left between them?

 

[Disco Volante]

I guess Ian already answered this? Since none of the transformers are handling very much power, you should be ok, but maybe try it out before cutting holes in some expensive fancy-box?
The field around a transformer increases enormously as you approach saturation, which is why power transformers are often "loud", being generally designed for high efficiency..

Happy tinkering;-)
Cheers, V!

 

[Walter66]

The big (phono) output trans will run 10mA, hoping it won't disturb the circuit at all. The bench test circuit will show which parts are hum sensitive.

 

[ruffrecords]

Could the phono out (big) and input (small) transformers placed side by side? Small one has 95dB of triple shielding, big one unknown.
Or should there be some space left between them?

Should be OK. Some Gates mic pres did exactly that.

Cheers

Ian