positioning output transformer on Fender build

[telentubes]

I headphone the choke as well as the OT. Find the quietest spot for both.
Here's my rig.. I soldered up a jack and use the Alligator clips on the leads.
Love that dead quiet idle.

thumbnail-4.jpg

[TUBEDUDE]

You want to use just the OT secondary with the phones, as you adjust it and the choke for minimum hum. That's what the speaker is going to reproduce. What the inductor sounds like is moot.

[xtian]

You want to use just the OT secondary with the phones, as you adjust it and the choke for minimum hum. That's what the speaker is going to reproduce. What the inductor sounds like is moot.

The choke is just a long length of coiled wire. Can't it receive induced hum just as effectively as the OT? Granted, it's very early in the HT chain, so presumably any hum is easily filtered out by the RC nodes downstream. Because of this, I agree, it's of little concern except WRT the OT.

[TUBEDUDE]

The choke also has a big ass pile of iron inside. When it is installed, or moved, it distorts the flux lines radiating from the P.T.
Apply power to the power tranny while listening to the O.T. secondary. As you move the choke about, you will hear the hum increase and decrease, as more flux lines intersect with the O.T. copper windings.
To be clear, the hum we are eliminating is radiated magnetic energy transmitted through the air. The filter cap string filters electrical current pulses moving through the wire.

[pjd3]

So, the positions have been had. It was still an interesting excercise whether it matters alot, a little or not at all. The OT ended up a little more than half way across the chassis about 45 degrees, and the choke was 90 degrees offset from the OT. I couldn't hear any hum/buzz from the speaker and very little from the headphones, and the chassis doesn't even look too ugly.
Now its time to over-ruminate about the wiring strategy to and from the OT. As always, please feel free to advise on that, or make fun of me for worrying about it.
As this project goes forward I do see the beauty of sticking to a classic design as not to have to "re-invent wheels". But, I got greedy, and those larger transformers started looking attractive. Plus ya know what, I probably will benefit from having a few more watts than I originally intended on. Its been scary hacking up a Princeton reverb chassis to fit that of a single channel Vibroverb but, its really not unlike builds or mods on various things at work, although this is my first guitar tube amp.

What I will be moving into next is positioning the eyelet board, and creating the Bias/balance board, wiring up those things, and of course, implimenting good grounding. Rob has already made some clear recommendations from grounding on his diagram of the 6L6GC Vibroverb so I will stick to that. I'll just be wanting to make sure the bias system is grounded in the best way, and to the right places.

Thanks everyone, appreciate your time and comments.

Phil

[pjd3]

Yup did something just like the pic. Used a quarter inch jack and grabbed some aligator clips, for headphones and speaker. Did the trick.
First found a quiet place for the OT then stuck the choke inbetween OT and PT and danced it around until it got even quieter. Did that a few times with different OT starting points. Worked quite well. I was fairly convinced I had found a good compromise of distance and position(s). .

Phil

[sluckey]

So, the positions have been had. It was still an interesting excercise whether it matters alot, a little or not at all. The OT ended up a little more than half way across the chassis about 45 degrees, and the choke was 90 degrees offset from the OT. I couldn't hear any hum/buzz from the speaker and very little from the headphones, and the chassis doesn't even look too ugly.

Now that you know how Rube would do it, take a look at all the beautiful layouts on this forum and show me one that looks like the layout was based on a headphone trick.

[TUBEDUDE]

20190505_145019.jpg

Here you an see the OT had to be rotated ~ 40°


This previous build (using the same transformer set) required a piece of angle aluminum to be chassis mounted as the OT needed to be rotated 90° sideways leaving the OT mounting flanges in the vertical plane, perpendicular to the chassis as you can see in the bottom photo ( sorry i got them out of order)

20190303_013508.jpg

This SE amp needed the OT angled to minimize hum, then i added the choke, requiring the OT to be shifted another 8° for the optimum ( middle photo).

[TUBEDUDE]

So even with the same xfmrs and chassis there is some variety in the inducted lines of flux. So one size does not fit all. Fender, Marshall and the rest plot the position of transformers for ease of manufacture. They will never be as quiet as a hand built amp with iron located this way, and a sensible grounding scheme.

[pjd3]

That is wild. Looks like a tube/tranny chess board game. Obviously some deliberate experimentation went into those. My amp looks tame compared to those.

After a nice caffience session at Starbucks here, I'll go home and cut out a board to mount the Bias balance and master bias potentiometers. Rob had showed his way of actually soldering the bias trimpot right to the balance trim pot but, I wasn't finding trimmers in the values and type so, I just got a couple of 2 and 3 watt 24mm linear pots.
I suppose the bias board can go in a traditional place and the grounding of that, power grounds and preamp grounds will go to the recommended placed from Robs illustrations.

Almost time to wrap this amp up and get it ready for Stan Day to look at, make sure I didn't make a bomb out of anything. I haven't blown anything up yet so, should be alright.

Thanks for your time guys, and the good photos. They are eye openers and just good to see.

Phil

[M Fowler]

My most recent Rocket combo build, now check those transformer fitment.

transformers.jpg

[TUBEDUDE]

Wow, that's bold! How did the hum test go?

[sluckey]

Where have I seen that before. Oh yeah, back in the '60s...

[M Fowler]

No hum, and exactly Slucky it's been done many times in the past.

Mark

[Colossal]

Where have I seen that before. Oh yeah, back in the '60s...

Wow, those Dynacos are sweet!