Power transformer proximity to input area

[pjd3]

Hello,

It would interesting and likely very helpful to hear your take on this.

Moving ahead with my stereo 6V6 Plexi build in a blank Twin Reverb chassis, I have considered using an Edcor XPWR096 PT that I have. The initial plan was to implement two power transformers, one for each channel placed in the end/rear corners of the chassis. This was both to keep weight at the ends but more importantly to keep them distanced from the input(s) area which is in the very center of the front of chassis. This seemed to give a good distance from PT to inputs enough to mitigate any threat to magnetic AC field into the inputs.

However, in an attempt to keep cost and time within acceptable budget I've seriously considered placing a single 335-0-70-335 @ 200mA power transformer in the middle/rear of the chassis, which would make some layout sense. BUT, that would put the PT 8.00" inches away from the inputs and input sections of the two turret boards that are at the very front of the chassis.

Do you think that there is enough distance to not cause notable hum interference? Or is there something extra that could be done in terms of shielding, plates, mounting, etc,,,, that might serve to minimize any PT interference?

I was gung-ho on having the two separate power transformers as that would enable adequate distancing but, since I have a rather nice and well-suited Power transformer in the house, I'm really wondering if I will be OK installing it. Of course, if it ended up creating hum, I would bite the bullet and go back to the original plan of two PT's. The boards are already built so, I need to stick with having the inputs in the front center of the amp. I like it better that way layout wise, especially the location of the controls.


Thanks for your input. Ha, this is a painful consideration!

Best,
PJD3

[bepone]

PT should alyaws be mounted at maximum possible distance from the inputs.. so at the far corner.

[Phil_S]

Not sure why you want 2. I see no advantage. What Bepone says - on one side. I've put weights in a cab to give it balance if it wants to tip over.

Maybe you should post your layout. My guess is that input in the middle is unusual. There is a reason why this isn't done. Put the OT towards the other end and you won't have the weight imbalance.

[pjd3]

Thanks Phil,

I'm not really interested in changing layouts unless necessary, if for some reason something isn't working I'll change it. My concern is if 8" is generally too close to expect no issues near inputs.

One advantage to 2 PT"s s that if say, a power tube had a bad cathode to filament short and a coil got burnt, there would still be an entire soveirgn amp as a back up. Although you'd be mono for a while, it wouldn't be a show stopper. Its value wouldn't be realized until that actually happened.

Best,

Phll D.

[Bergheim]

If the B+ supply and heater branches for the two channels have their own fuses, you would still have the same backup/redundancy with a single PT compared to dual PTs, except for a failure in the PT itself. Which is very unlikely as long as the HT and heater winding are fused correctly.

[pdf64]

Sound City amps tended to have their transformers at either end of the chassis, with the mains transformer within 2" of the input sockets. As I recall the transformer core was in the vertical plane, so not 'firing' at the inputs.
This didn't cause any hum.

[sluckey]

The Ampeg Super Echo Twin (ET2) has a very similar layout as your plan, PTs on the end, inputs in the center.

[pjd3]

Thanks all,

And Sluckey, it is heartwarming to see that amp with the nice little PT"s at each end out of the way. You may have missed that that was my original plan (and still may be) but, I"ve opted to seriously consided putting a single and bigger PT in the rear/middle of the amp, as I can save money and time. My fear is that it may have been to close to the input sections eminating from the front/middle on out. There is a little over 8" from front to rear of a Twin Reverb chassis.

But as mentioned, there was a commercial amp who's PT was only a couple of inches from the inputs, with care taken to not aim the radiating field at the inputs. That gives me some semblance of hope that this could work.

Thanks so much all!
Best,
Phil D

[timrobertson100]

PT in the middle, inputs and OTs on opposite sides, and just swap the boards you made over?

Using one PT seems to make more sense for this build to me, as opposed to just building 2 amps.

[pjd3]

Aw Timbr,

It would be a tempting idea if all the holes weren't already drilled for pots, switches and power lights!

Plus, I really prefer the start of the preamps at the Mid/front of the panel. If I didn't drill those holes and somewhat commit to the panel layout though, that would be the sensical thing to do.

I'm still considering going two PT's in each far corner of the chassis. The PTs I have my eye on are $99 bucks a piece and provide 130mA of HT current, and the one I have at home provide 200mA total of HT current making 100mA per channel. Both would probably be fine as the amp will be consistently used at a relatively low-medium volume (pedal platform with zero-loss FX loop) and never cranked anywhere near its full potential. I've gotten about as low volume as I can tolerate with band members still saying "I think you're getting a bit loud there, Phil".

Thank you,

PJD3