Strange HUM.....

[M Fowler]

I still think it is a PT that is humming due to it's construction not it's orientation.

But it's anyone's guess what the real problem may be without eliminating all possible sources already described above.

Mark

[RJ Guitars]

I still think it is a PT that is humming due to it's construction not it's orientation.

But it's anyone's guess what the real problem may be without eliminating all possible sources already described above.

Mark

It's entirely possible... I have certainly seen that before. If you have a hum from the amp itself and it doesn't go away when you unplug the speaker, then it's a mechanical vibration. Simple enough to test.

[rooster]

surfsup, yes to rotating (ideally) your PT, and facing the end bell of the OT towards it. Just the opposite of what you did, but I am not saying you didn't do things following proper layout, just that doing it the other way would be slightly quieter.

OK, the picture you posted of the 'standup' tranny is what you would have IF IF IF you layed your PT on side. Do you see this? Your tranny positions are just like Don's, two donuts standing upright, although yours are lining up to the null points. So Ken opted for the PT having it's coil lying on it's face, an improvement, because the eddy currents are even further disoriented.

And this is a language thing here, too, surfsup. The word 'standup' as it references a tranny means that it is surface mounted on feet, or standing up - that's all. It does not qualify whether the coil is standing straight up (as in your's and Don's case) or lying on it's face as in Ken's design.

Okay?

[don280z]

M Fowler:
The PT is not humming or vibrating.
ALL of the hum is from the speaker.
If I unplug the speaker, the hum stops.

[rooster]

Don, yes, I see where your PT was originally. And this would be identical to surfsup's layout...except he has a lot more separation of the two. I really don't care if it's a Rocket, either. He has you beat on the separation.

OK, I'll be looking at your gut shots later today, but ultimately you need to think about this tranny layout at some point. There's a science here that can't be ignored. In a nutshell, the amp's layout, whether the 'hard parts' or the wiring that connects them, will either punish you or reward you. In your case, I can see you are a free thinker and I applaud this. Many here who build these TWs simply follow the pics and do pretty well actually. I will offer at this point that your path is different than theirs - because you are learning why Ken Fischer's layout works and yours does not. You may hate the process right now, but you are learning something that the others may never know. Don't discount this, Don. Take care.

[jelle]

What happens when you have the Powertransformer running and there is no voltage on the center tap of the output transformer? Do you get hum from the speakers? If so, inductive coupling, if not then the transformers are positioned correctly. You may have to desolder the center tap wire from the B+ to test this depending on your layout, but this is a very easy test.

Good luck and let us know,

Jelle

[RJ Guitars]

What happens when you have the Powertransformer running and there is no voltage on the center tap of the output transformer? Do you get hum from the speakers? If so, inductive coupling, if not then the transformers are positioned correctly. You may have to desolder the center tap wire from the B+ to test this depending on your layout, but this is a very easy test.

Good luck and let us know,

Jelle

what he said +1

The standard Wreck configuration has the HV going to the OT after the HV (standby) switch. But as Jelle points out, your layout may do this differently.

I loved the trainwreck work and used many of those ideas in my own designs. I especially liked the way the Wreck layout made room for tubes with nothing in the way. On one of my builds I confidently followed what I had learned and ended up eating some crow in sorting out what sounds to be a similar hum issue. SE amps hum a bit anyway so I thought nothing of it in the prototype... but this hum was different. Not a vibration but an instantaneous hum when I hit the power switch. I ordered a dozen chassis but after the fact that hum started to bug me. I did the headphone trick and this was as close as I could get them to one another without the return of the hum. You can see how I cleverly plugged the holes and moved the tranny.

FWIW - I am going to give an educated guess that some transformers are friendly toward one another in differing orientations. So what worked for Ken Fischer may not work perfectly for the rest of us unless we use identical iron to what he was using. Could be that a slight difference in the wind or the iron or whatever...

I think you are making progress in understanding the problem... keep in mind that things could still be different than my own experience.

rj

[rooster]

OK, I agree. The photos are helpful, BTW, Don.

Can you find the center tap of the OT primary? Is it on the bottom (top) of the standby switch? OK, unsolder it wherever it is, just as jelle suggests. Now turn the amp on.

(NOTE: Sometimes people make mistake a here and attach the OT center tap to the 'charged' side of the Standby switch. If this is the case, the OT is getting voltage but not screen voltage or signal, so it hums. )

Does it still buzz/hum?

[don280z]

The power transformer goes through the diodes then to the first 40uf filter cap stack.
Taps off the stack and runs to the center leg of the standby switch. (single wire)
Runs from outside leg of the standby switch (2 wires) to the OT and the rest of the resistor/cap network (B+2, B+3, etc).
NO power to the OT until standby switch is operated.
PT center-tap is chassis grounded with the filter caps.
PT is 300-0-300volt.

[jelle]

Thanks. So, does it hum with the power engaged and the standby in the "Off" position?

If so, inductive coupling, if not, then it is something else.

Please let us know,

Jelle

[don280z]

jelle....Yes it does....I believe it is inductive coupling....

[jelle]

Ok, then you have your answer. Sorry to hear as moving transformers is more work than moving grounds....

I think that the guys have provided quite some info on how to place the transformers. If you need more info, please ask!

Good luck, you are one gigantic step closer. Knowledge is power!

Jelle

[don280z]

jelle.....Next time I have the amp 'open', I will try moving the PT center-tap ground.

What is strange is, this is the 2nd TW amp I have built.
Both are identical wiring - even the transformer placements.
This one hums....the other one doesn't......
SAME transformers......

I might throw an oscilloscope onto the output to see which frequency I am hearing......

[jelle]

I'm confused by your reply....we just assessed that the cause was inductive coupling.

Why not fix this issue before doing something else? The systematic approach is much quicker and more secure. Plus, you will wear out the ones who are helping you.

Jelle

[don280z]

Oh....Very sorry....That was supposed to directed to rooster.... He suggested moving the PT center tap ground to see if there were any ground loops.