transformers extra windings

[zorro]

What is best to do with the extra windings that you don't use on the power transformer? Do you cut them back or coil the up just incase you might need it for another project or addition. I am chasing a 60 Hz hum on a 5E3 I just built and am wondering if the long wires hanging off the side of the chassis is causing part of the hum.

[stokes]

I usually just cut them short and shrink wrap the ends to insulate them.Have never had a problem with hum from extra windings,of course if you have long lengths of wire from the windings it could cause a problem.Are you sure it is 60hz hum?If so,try connecting the heater winding CT to the cathode of your power tubes,instead of grounding it,or if you have no CT and are using the 2x100ohm ground reference, instead of grounding them, connect them to the cathode.It gets the heaters ground reference above and out of the signals ground path.

[zorro]

Filament power is DC

I am running the filament supply on DC. I put in a 25 amp bridge with a 6800 mF capacitor. I did not ground the center tap. Do you think I should?

[zorro]

You nailed it

Stokes thanks!!! I just grounded the CT of the filament transformer. That took almost all the hum out. I have the amp at full volume now with only a minor amount of hum. I tried connecting the CT of the filament to the cathodes, it has the same effect. Thanks again.

[Bruce / Mission Amps]

Wait... I hope I am not misreading something here, but if you are running a 6.3vct PT with a bridge rectifier... you can not ground the center tap of the secondary, and with it hooked up right, you should be seeing something like <+9vdc here and less fully loaded.
The grounded anodes of the FWB recitifer is the ground point.
Have you measured the dc voltage of this arrangement with and without the center tap grounded?
Actually, with the center tap grounded, I'm suprised the recitifer block didn't blow up or the PT over heat.

[zorro]

Back to the drawing board

You are reading it right. The hum went away but the PT did start to heat up when I grounded the CT of the PT. I am running the filament circuit with a 25amp full wave bridge rectifier. I am getting a clean 6.3 volt DC with all the tubes in, with or without the CT grounded. Unloaded I was getting 8.7 volts DC (in the ungrounded CT version). I have to say, I added the reverb circuit section of the Fender Princeton amp to the 5E3. I better get back to that addition and see if it if the cause. I thought I eliminated it as the cause, but I might have wrong in my reasoning.
So it's back to the drawing board to trouble shoot the hum.

[Bruce / Mission Amps]

OK... can you scribble up a schematic and take photo of the layout?
My old SoulKicker Reverb amp is a modified tweed Deluxe with 6L6s and reverb.
However, I NEVER needed DC filament suppy on it, or any amp I've ever made for that matter.
If your filament is causing the hum, quickly disconnecting the grounded anodes of your FWB rectifier should eliminated the hum instantly, but the tubes will still amplify and make sound for a few seconds when cooling down.
If it doesn't instantly stop the hum... it is not the filament supply.

[zorro]

Some success &amp; pictures

When you mentioned lifting the ground, I thought, oopps, what ground. Now I understand why you said you were surprised that the diode bridge didn't fry. I didn't have the common anode side of the bridge grounded. I left the entire supply floating and didn't think it would make a difference.
I just grounded the anode common to ground with a .047 mfd 600v cap. I didn't have a .1 mfd. It knocked down the hum to the same small amount I had when I grounded the CT of the filament transformer. The PT is overheating. But I had the volume at max for about 15 minutes with the small amount of hum. I did not run a signal thru it for long.Maybe I didn't keep the amp running long enough when I didn't have the ground attached and it still was over heating. I just removed the capacitor to ground and will let it stay on for a while to see if it does over heat or not.
The pictures do not show the capacitor that I just added.
I didn't get to a scanner, so I couldn't show my circuit modifications. I appreciate your help.

[Bruce / Mission Amps]

OK first things first... if you did not ground the anodes of the FWB then you are only using two of the diodes as in in a FW rectifier circuit... this means you have to ground the center tap of the filament supply but that will only net you.. 1.4 x 3.15vac or 4.4vdc, with a big filter cap.... what this means to me is that something is not quite right in what you are telling us.
However, if you lift the center tap of the 6.3v windings from ground... and ground the anodes of the FWB block instead, you'll get twice that voltage.
You have .047uF, but I think with a bigger grounded anode cap, I think it will still work as a FWB but with less output voltage as the impedance of the circuit will be different.
I'd have to mock this up to be sure.

What I would do is take the DC supply of and discard it as it is really unnecessary.
Instead, take your green yellow 6.3v center tap off the grounded side of your buss bar behind the filter caps and move it to the cathodes of the power tubes for a 20VDC bias.
Also you need to move the center tap of the high voltage supply off that ground lug and put it where the green/yellow 6.3v filament lead is now... right at the negative end of the first filter cap.
I'd also consider taking reverb recovery triode's cathode biasing resistor and it's cathode bypass cap off the board and putting it right at the same place your reverb tank jacks are grounded to the chassis.
You have WAY too many daisy chained grounds leads on your eyelet board.

[zorro]

I'll give it a try

I guess I was not explaining myself clearly. This is the way I connected the FWB before any grounding of the filament windings.


Also the green yellow wire you see going to the buss bar is from the ground lug of the PT. It isn't the 6.3V CT. The daisy chain ground leads on the turret board are all one continuous 20 guage wire I wrapped around the turrets and left insulation when jumping over to another section. I felt I should not have any resistances developed as I might if I used pieces daisey chained. Is it still an issue.
I will try your suggestion and wire the supply without a DC bridge configuration.
What is considered normal heating of the transformer? I would think it should be cold if not just a little warm. I am using a Weber W041318 PT.
I might not be able to try this until tomorrow. Thanks again.

[Bruce / Mission Amps]

Ahh... I see... that power supply schem looks fine and the .1uF cap to ground should be OK too.
OK on what you think the the green/yellow wire is for... BUT, that's a bad choice of colors for most modern PTs, as it is the color commonly used for the 6.3vac filament winding center tap... so, are you sure?
Why I ask?
The W041318 tranny number you gave is an output transformer.. similar to a silver face Deluxe Reverb OT... it will work but that OT has the wrong impedance for a 5E3!
However, if you ment to type W025130 as the power tranny... then the green/yellow wire 'IS' the 6.3v filament winding center tap and with a FWB should not be connected to chassis ground.

For an improved filter, look at my modified schem below, and use two of these caps in series with the G/Y wire connected to the the junction of the + and - lugs. The proper hook up for a FWB in this application is still going to give you over 8VDC though...
6 amp Si diodes in series with the B+ will drop about .6v on every one so you can lower it a bit with some big, low voltage high current diodes.

http://www.rs-components.com.au/1/69...2000uF16v.html

Those Chinese transformers always run a little hot.. they are NEVER cold when the amp is up and running for any time at all.

You should not have your first preamp tube's cathode biasing resistor grounded into your daisy chain... move it to a grounded lug right at on of the input jacks.

[zorro]

I was rushing

I am starting to worry about myself, that if I can't post the right information, I better triple check my wiring.
The W041318 is the output tranny as you noted. Weber specs it as good for the Deluxe and Deluxe Reverb. Which is why I purchased it. Weber's power transformer made for 120VAC was on backorder so I order the W025130EU, which still has the tap for 120VAC.
The green and yellow wire was extra wire I had from a power cable. It's not the center tap winding. Most of the wiring is not using formal colors that most seem to be using. I had it handy so I used it.
I took out the DC filament supply as you suggested in the previous thread and the hum is no greater than the DC supply with the DC rectifier bridge wired properly. So the loud hum is gone. I might later play with the DC filament supply after I get rid of the very small amount of hum I have now.
I will do the other suggestions you gave me.
Bruce, I have to say, I am impressed with your knowledge in trouble shooting with the scant information given in a post.
Thanks for your patience.
George

[Bruce / Mission Amps]

OK if for some reason the PT filament secondary does not have a center tap... use the 100 ohm resistors across lugs 2 and 7 of one of the power tubes and where they connect together in V... put that junction to lug 8 of one of the power tubes.
If the PT does have a center tap... which I know the W025130 does, use a 47 to 100 ohm resistor on the end of that wire and connect that to lug 8 of one of the power tubes.
This will put a DC bias, equal to the power tube's bias voltage as developed across the biasing resistor, .... on the filament supply.
That will reduce some of the hum too.

[zorro]

down to the reverb

Bruce, thanks
I got the rest of the hum down to the reverb section that I added. I disconnected the reverb and I have no hum. I also might be loosing some gain in the way I added the reverb. I could keep it out and it would be hum free, but the reverb does work, just not optimally. So I will continue to play with the reverb addition.
I took the circuit straight out of the Fender Princeton amp schematic. I figured it would need tweeking. This is my starting point. The amount of reveb is fine. I would be satisfied with even less reverb if I can get rid of the hum and get the gain right.

[zorro]

progress

I changed supply for the first stage of the reverb circuit from the first caps approx 400vdc to the second filter caps 360vdc. It is down to the hardly any hum. Actually it's the same amount I had when I removed the reverb circuit. This thumbnail is only different by the supply voltage I mentioned.