Strange HUM.....

[T Wilcox]

Hey Surfsup

Thanks, did not mean to sound like an ass in my reply, but was just curious what purpose a resistor would have across the standby.

Thanks for the link, Merlin sure knows his doodoo

Todd

[FUCHSAUDIO]

It's magnetic waves from the PT getting picked up by the OT. Again, add the shield, move or rotate the output iron.

[rooster]

surfsup, man.
Merlin visits here and I know that, but I will still say that:

1) This add on stuff he suggests should always be gauged against what has already survived these 60 years in guitar amp building.

2) Theory vs. fact, in the field of guitar amp building, is fun reading sometimes.

3) Beyond expressing theory, a quality sceintist still builds a concrete example to prove his point.

4) Merlin don't build guitar amps.

5)

[rooster]

don280z - What is the brand of the PT?

[surfsup]

Guys I was just asking if there was a resistor on the standby. then I just responded to a question posed to me why someone would do such a thing. That's all. I don't want to get into a Merlin-validity argument.

Rooster, you seem to really know your stuff. My post had nothing to do with you and I never stated Merlin was the end all knowitall...

Hey looky there, its Friday!

[don280z]

rooster.....
PT is a Hammond
OT is Mojotone

[rooster]

Ha! Well, you have got a very quiet PT there. Of this I am sure.

So then I need to know one other thing. Follow me on this please. If the OT is making sound at the speaker, then one glaring opportunity for this kind of noise is that the filament supply is somehow being picked up by the primary of the OT. How far away are the internal filament wire attachments from the primary of the OT?

Did you use the filament center tap of the PT, or did you cap this and use the 100 ohm resistors like Kenny did? I highly recommend the use of the 100 ohm resistors, BTW, this is always a better balance than the center tap method. Um, it's been proven to be quieter, in other words and I agree.

I never saw a pic of this amp so maybe you could post one for all to see. Right now I am thinking layout trouble.

[M Fowler]

I highly recommend the use of the 100 ohm resistors, BTW, this is always a better balance than the center tap method. Um, it's been proven to be quieter, in other words and I agree.

Edcor was surprized that I would ask for a PT with filament supply CT as hifi guys don't use a CT, live and learn.

Mark

[T Wilcox]

Not trying to hijack this thread, but since I have exact same issue as OP with MC iron rather than Hammond. Here is thread with my gut pics as is.
Please point out any errors that would cause this if you see any Rooster!

BTW my heater ckt is center tapped, but i aint Kenny

https://tubeamparchive.com/viewtopic.php?t=15348

Thank you and have a great weekend

Todd

[don280z]

rooster....

Transformers are 1/2" apart, turned 90 degrees.
Heater is 6.3V center-tapped and grounded.

I will take your advice and remove the center-tap and ground the 6.3V through a pair of 100ohm resistors. I did it this way on my last build and didn't have any noise issues.
I'll keep you posted...

[rooster]

Todd - OK, do you not see what you did that could be a problem?

1) As the filament wires exit from under the board, are they twisted around the OT primaries? Wow, why would they even be coming from the same direction, the OT is to the back of the chassis. ?

2) At the connections of the OT primaries to the power tubes - do you think the filament wire should be laying on top of them?

3) Use the 100 ohm resistors

OK, look at V5. If you were to attach this long filament wire - you know the one - directly over the top of the socket and away from other wires, in a straight line basically, pin 7 to pin 2, you would at least get it away from where it is, which is too close to the output jacks, etc.. You have to remember that one way to reduce stray hum from the filament wires is to evenly twist them right up to the point of contact with the tube socket.

FWIW, I always do my filament attachments like Fender did - up off the board and twisted fairly tight. Yes, I know, Ken did his the Mashall way, not taking issue. I would still suggest that Ken's way looks quite different than yours. It may be subtle to you, but there are vast differences. Look harder.

Alright, hope this helps, have a good weekend.

[rooster]

don280z - You said 1/2"? You need to max this out. 1" is pretty easy to do, is there a reason why you chose 1/2"? When I build these amps I just pull the trannies as far apart as I can. I realize there is an issue with the front cab 'plate', but again, 1" is pretty easy to do.

So, since I have never dealt with the 1/2" dimension, it may be possible that you have created a problem that I am not addressing. Here, it may be possible that you have set yourself up for some type of eddy current interference. Hard for me to know.

Q: Can you to separate them further?

You may have to do this.

[T Wilcox]

Hey Rooster

Thanks for checking it.

I actually was not troubleshooting this problem until this thread came up today! The problem was/is so minimal and unnoticeable while playing or even being more than 2 feet away that I was not concerned.
Well you just pointed out my #1 mistake, I mounted the damn OT with the laminates parallel to the PT's laminates. Arghh. Dont know what I was thinking when I did that.

Anyways thanks again, looks like I have some work to do!

I will address the other problems you mention as well!

Todd

[Bob S]

Put a decent star washer above & below the power transformer fixing screws. Even scrape the paint where the star washers make contact with the star washers. Run a separate ground wire direct from the incoming 120 vac ground to one of the transformer fixing screws.
Worked for me.
Good Luck!

[Clyde]

surfsup, man.
Merlin visits here and I know that, but I will still say that:

1) This add on stuff he suggests should always be gauged against what has already survived these 60 years in guitar amp building.

2) Theory vs. fact, in the field of guitar amp building, is fun reading sometimes.

3) Beyond expressing theory, a quality sceintist still builds a concrete example to prove his point.

4) Merlin don't build guitar amps.

5)