positioning output transformer on Fender build

[pjd3]

Hi there.
So just got a T03MT output tranny and a choke arrive. I'm caffiening up at Neros and then going home to spark up the PT and do the headphone trick.

I pretty much get how and why to that but would sure be interested to hear comments on dealing with the choke position, if that has any bearing on things. Someone did say something about the choke maybe deflecting some magnetic waves from the PT and re-introducing some noise. This could be bulshit but, how would I know?

In your experience did determining the position of the choke come into play with finding the lowest noise condition of your tube amp?

Thanks everyone, board is complete and rectifier tube socket, power switch is wired up.

Phil Donovan

[xtian]

That was me, and it wasn't BS (though I applaud your skepticism!), it was experimental evidence, and easy to repeat the experiment yourself. First, position your two trannies for minimum noise, using the headphone trick. Then position the choke in between while listening. I'm sure you'll be able to hear if the choke bends the magnetic envelope in a way that reintroduces noise.

[pjd3]

Thank you xtian, (and I appreciate that you support my skeptisism! good man!). So yeah, thats a good piece of experimental finding. i'd hate to find the perfect OT position and then cluelessly shove a little choke in there and destroy 8 hours of neurotic rumination over my precious OT positioning. And I'll assume this can all be done effectively under recommended conditions - PT secondaries are dis-connected and taped off. (The PT is already mounted)

xtian, could you fill me in on how you wired the headphones? the full OT secondary coil into one side of the headphones? Or was there a more complete method of getting the OT seconardy into both sides of the headphones? Sure, I'll try different configs but, curious to your findings.

thank you again, I sure appreciate your feedback, helps to move along well.

Phil

[TUBEDUDE]

I have also found the positioning of the choke to change the flux lines, just by the magnet mass as it sat with no power. Connected, as it draws current, it changes a little more. I hook both headphone channels to one side of the OT secondary, bridging the ring and tip with a test lead that has a large alligator clip. The other secondary lead to the sleeve of my headphone plug.

[xtian]

^ That's a good approach. I just connect OT secondary common and any tap to headphones and listen thru one ear.

[pjd3]

Thanks guys, ready today to do it, I'll most likely try both headphone set ups just to see how they both work, and might as well try both the 8 and 4 ohm taps. Its just an alligator clip switch and who knows, maybe one way will be more revealing than the other. Or not!

Thanks,

Phil

[TUBEDUDE]

One of the taps will be louder letting you hear better.

[pjd3]

Hey thanks so much for coming around everyone.
So, I'm here with the PT (Mojotone Bassman) mounted and running and the TO35MT (and choke) riding around on the chassis with the secondary (8ohmtap I thinks) going into a Line 6 pod, see if I could get some more amplification that way. (and it is lounder than straight headphones)

It bugs me that the most quiet position is when I tilt up one side of the OT about 45degs. ha, damn, figures.

But, moving around the OT alone, no matter the angular position to the PT it is generally much more quiet all the way at the other end of the chassis. And then moving the choke all around between the PT and OT that yields various level of quieter, and different timbres of buzz and hum. The variety of OT positions yields varying timbres of buzz and hum too. Also, it seems that lifting the OT physically off the chassis makes it quieter - touching it back down brings some buzz back. Not sure what that is. (could be the POD ground adding stuff in also. I got this chassis for 44 bucks from Ebay, I think it may be steel as opposed to aluminum, not certain though. I heard someone say (Get Aluminum! Dont get steel! The steel will raise havoc with electromagnetic transfer!) Something to that?

So, in placing the OT and choke, maybe I should mention that this amp will almost never be cranked. It was built to be a clean machine pedal platform that will never be more than light to moderately loud in small to medium size clubs. I expect it wil be around 40 watts or so. Its going to be miced and more of a personal stage monitor for me than an amp thats meant to fill up a room by itself. So, with that application in mind - Will I need to be as concerned about live hum and buzz as opposed to if it were cranked up to get natural breakup from it? For loose comparison, my stage volume is like you had a Pro reverb on "3". Very clean, no breakup, working good, but not ear splitting.

Another thing that occurred to me, and this is only a curiosity, not a call. If the non-amplified induced hum and buzz from PT and OT proximity is such that its not very loud at all through headphones or even a Line Six Pod, then how would that hum manage to be audible through a large 12" speaker that has super amplified electronic noise in tandem? Wouldn't the amplified hiss hum and buzz mask the low level induced hum between PT and OT? I'm sure thats just my lack of practical experience but, that notion was pecking at me.

Anyways, I'm definately continuing to locate what I find as the quietest combination of OT and choke position. Its a very interesting process.

My one last concern is, will I need to be aware of inviting issues by having the OT nearing the other end of the chassis? Will the OT wires tend to induce things into the preamp area of the eyelet board and wires to the pots? I suppose when my amp tech gets his hands on it he could take it upon himself to undo any undesirable symptoms I have brought into the amp. But anyways, having fun with this.

Thanks for your input, means alot to me and first amp build

Phil




OT pro

[xtian]

By mounting the PT first, you locked yourself in to that orientation. But rotating the PT 90 degrees might solve the issue!

This hum we're fighting to reduce will only be noticeable at idle. In a quiet room, you may hear it from a distance if it's bad, or only by putting your ear up to the speaker if it's minor. But for me, I consider a professional build is only professional if the amp is near silent at idle.

Also, you will hear this hum while in standby, with no amplification happening at all.

Yes, you can place the OT on the far side of the chassis, and yes, you should keep the OT wires away from sensitive input preamp stages.

You know, you can get just as effective a result by hooking up an actual guitar speaker rather than headphones, and you'll hear the hum just as well. Remember, playing a 1/10th-watt solid state amp through a full stack makes a wicked noise!

[sluckey]

Fender had a very successful layout. It's doubtful you will improve it . I would just copy that layout.

[pjd3]

Thanks but there isn't actually a classic layout to go by at this point, its a princeton reverb chassis with a Bassman PT.

Plus, I'm not trying to improve on anything, just trying to learn something, have fun and make the best of what I have.

Phil

[M Fowler]

I have never worried about all this in my 200 or so builds.

Any issue I had with noisy PT was defective PT verified by the builder of said PT.

If a Trainwreck Express can work without problems then about any layout you can dream up will work.

Yes I do orient the PT, choke and OT as any amp company would, say Fender or Marshall.

Headphones are for listening to music.

Mark

[xtian]

I have never worried about all this in my 200 or so builds...Headphones are for listening to music.

Why, you fossil. I'll bet you're too deef to hear the hum, any-whys.

[didit]

Why, you fossil. I'll bet you're too deef to hear the hum, any-whys.

Careful youngster. Heed wisdom of elders for ancient & obsolete technologies.

[M Fowler]

Xtian, how did you know the ears were gone!