I recently completed a build of one of Pete Millett's designs using an Edcor power transformer and notice there is a loud buzz/humming noise.
The transformer can be wired for 120v 50/60hz and also 240v 50/60hz, and I've measured the voltages, so it is definitely wired correctly.
Edcor suggested to tighten the screws on the transformer or tap it with a small hammer....neither of which resulted in any difference.
The hum/buzz is also there when I remove the tubes from the amp, hence it cannot be drawing too much current for the transformer.
A friend of mine is an electrician, he brought along a frequency and voltage converter (very expensive piece of equipment) and when he converted the frequency from 50hz to 60hz, the buzzing goes away almost completely.
Is there any way of fixing this issue - or is it simply best to return the transformer (postage costs from Oz to the US are obviously prohibitive).
The transformer can be wired for 120v 50/60hz and also 240v 50/60hz, and I've measured the voltages, so it is definitely wired correctly.
Edcor suggested to tighten the screws on the transformer or tap it with a small hammer....neither of which resulted in any difference.
The hum/buzz is also there when I remove the tubes from the amp, hence it cannot be drawing too much current for the transformer.
A friend of mine is an electrician, he brought along a frequency and voltage converter (very expensive piece of equipment) and when he converted the frequency from 50hz to 60hz, the buzzing goes away almost completely.
Is there any way of fixing this issue - or is it simply best to return the transformer (postage costs from Oz to the US are obviously prohibitive).
I'm wondering if the primary inductance is insufficient for 50Hz operation? I assume you operated it at 240V, 60Hz?
Do you have any means of measuring the excitation current and power consumed (real and imaginary) unloaded at 50 and 60Hz and comparing?
Do you have any means of measuring the excitation current and power consumed (real and imaginary) unloaded at 50 and 60Hz and comparing?
Good points. About the best I can do use a consumption meter to take readings of (a) amps consumed, and (b) watts usage. I can measure these figures at both 50hz and 60hz operation. This is obviously at idle. Will this provide any meaningful data?
Does that meter include options to measure power factor, current, and power in real watts and VA? Even measuring the current may provide the required insight if it increases significantly at 50Hz..
if i were designing that traffo, i would compute for 50hz as a 50hz traffo will have no problem running on 60 hz, while a 60hz can have issues running on 50 hz...
the humming sound can mean that the traffo operated very close to the saturation point/knee....
humming aside, if your magnetising current is such that the traffo heats up without load, then that is a giveaway that the traffo
did not have enough turns on the primary winding...
the humming sound can mean that the traffo operated very close to the saturation point/knee....
humming aside, if your magnetising current is such that the traffo heats up without load, then that is a giveaway that the traffo
did not have enough turns on the primary winding...
This is my suspicion, a substantially higher magnetizing current on 50Hz would be pretty conclusive. (Pull all of the tubes and disconnect the rectifier if solid state)
Ok good suggestion, I'll use the frequency converter to test the changes in the current drawn.
yes I read on rod elliott sound pages that going from 60hz to 50hz can be troublesome...
I know for certain that the idle consumption (with the 13EM7 tubes inserted in the circuit) measures only 0.24A and about 40W. Strange as the datasheet of the 13EM7 gives a filament draw of 450mA. The power tranny is rated at > 1A and doesn't get hot.
One additional thing I tried was to use a 240v -> 120V stepdown (still 50hz) and the buzzing disappeared as well.
So it must be a combination of the higher voltage and the frequency which is causing the core to buzz...
I pulled the tubes but the recitifier is already soldered to the tranny so that's a little tougher.
Certainly without the tubes in-circuit, at 240v 50hz the buzzing noise level remains the same as if the tubes were still in-circuit....
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About as loud as a bee or a wasp in the room, enough to be be a nuisance in quiet passages of music! I considered wiring a 13v DC supply to the filaments to reduce the stress on the tranny, but that doesn't solve the issue at all.
Using a 240v->120v step-down and then re-wiring the mains of the transformer is an option, but that obviously might put stress on the step-down tranny. How can I determine the peak current drawn by the amp (circuit is attached) in order to buy the correctly rated step-down transformer?
Using a 240v->120v step-down and then re-wiring the mains of the transformer is an option, but that obviously might put stress on the step-down tranny. How can I determine the peak current drawn by the amp (circuit is attached) in order to buy the correctly rated step-down transformer?
i have a 6V6 pp amp that was brought to Australia by a Pinoy balikbayan, i incorporated a slide switch so that he can use it at 240volts and 50 hz....it's been there for about 2 years now and still runs okay....
if that traffo is not heating up that much, then dipping it in electrical varnish could help, you may even try wedging popsicle sticks between core and bobbins to tighten up the laminations.....
if that traffo is not heating up that much, then dipping it in electrical varnish could help, you may even try wedging popsicle sticks between core and bobbins to tighten up the laminations.....
The Edcor power transformers are pretty good quality so I am surprised about the issue. As I think about it you might want to talk to Edcor about the issue.
My usual rule of thumb for auto-transformers is 2X the Va rating of the device to be powered. (I grow up overseas and had some 120V stereo gear, this provides good voltage regulation under the varying load imposed.)
My usual rule of thumb for auto-transformers is 2X the Va rating of the device to be powered. (I grow up overseas and had some 120V stereo gear, this provides good voltage regulation under the varying load imposed.)
hi,
It seems that the windings moving are your problem with the buzz, a amp clamp will tell if your over amppin it, Now here is what I did to fix one I wound,I put a bicycle air fitting in the top of a clean gallon paint can,I put the transformer in and the transformer shellack about a inch above it and hammered the lid shut(they make metal clips to keep the lid on),I took a tire pump and pumped 15 lbs on it ,and left for a few days,Then I took it out and put it in a warm place and dried it about a week ,it just about quit stinking,lol.Plugged it in and no buzz,it did stink for a few days butt went away,I guess it was totally dry then , I was a happy boy! Never used Popsicle sticks, if it works,good by me!
A Happy New Years To ALL
NS
It seems that the windings moving are your problem with the buzz, a amp clamp will tell if your over amppin it, Now here is what I did to fix one I wound,I put a bicycle air fitting in the top of a clean gallon paint can,I put the transformer in and the transformer shellack about a inch above it and hammered the lid shut(they make metal clips to keep the lid on),I took a tire pump and pumped 15 lbs on it ,and left for a few days,Then I took it out and put it in a warm place and dried it about a week ,it just about quit stinking,lol.Plugged it in and no buzz,it did stink for a few days butt went away,I guess it was totally dry then , I was a happy boy! Never used Popsicle sticks, if it works,good by me!
A Happy New Years To ALL
NS
A good link to how to wind a transformer and a simple excel spreed sheet to do the math for you !
http://ludens.cl/Electron/trafos/trafos.htm
NS
http://ludens.cl/Electron/trafos/trafos.htm
NS
I've noticed that on one side of the transformer there is a little metal clamp between the bell enclosure and the core. See the attached pic, I've circled it.
On the other side there is no clamp. Could this potentially the problem?
For the output transformers, I can see that there are clamps on both sides, so possible when the power transformer was made (I've read that Edcor make all their transformers to order), they've missed this part of the assembly?
On the other side there is no clamp. Could this potentially the problem?
For the output transformers, I can see that there are clamps on both sides, so possible when the power transformer was made (I've read that Edcor make all their transformers to order), they've missed this part of the assembly?
Attachments
If you can, try measure the magnetizing a.c. (that is current!) drawn by the primary (i.e. with nothing connected). You can do this either by an a.c. current meter in series, or lacking that on your multimeter, a resistor of say 10 - 100 ohm in series and measuring the a.c. voltage across the resistor. This should result in about 5% of the VA rating of the transformer; certainly not higher than 7%. That will reveal whether you are saturating the core
....which I am going to guess you are not. Any good power transformer should not be in order for 60 Hz and suddenly draw such a magnetizing current at 50 Hz that an objectionable hum arises (though anything is possible). I have worked on several amplifiers from the USA and have never experienced a troublesome increase in magnetizing current/heat here in the RSA (we have 50 Hz mains). You can also sweep round the core with a piece of sheet steel; it should not pick up serious magnetism anywhere.
My guess is rather that 50 Hz 'strikes' the mechanical resonance of a loose lamination. If this proves to be the case, some serious investigation might be required to silence it. Open up and try all manner of pressure everywhere, also jamming something thin between winding bobbin and laminations; a table knife or whatever - with the necessary safety precaution for shock.
With the core securely clamped (not over-tightened!), it is unlikely that somewhere inside where you have no access, something will be vibrating to a troublesome extent. Examine the core: Are all the "E"s and "I"s in place and properly touching each other?
Etc. When you have located the problem, you can usually pour/squirt some varnish/whatever into the region or some spacer somewhere. I hope you are successful; I occasionally had to use patience, but have always found some form of loose lamination. Don't ignore the shell; that can also vibrate where touching the core!
....which I am going to guess you are not. Any good power transformer should not be in order for 60 Hz and suddenly draw such a magnetizing current at 50 Hz that an objectionable hum arises (though anything is possible). I have worked on several amplifiers from the USA and have never experienced a troublesome increase in magnetizing current/heat here in the RSA (we have 50 Hz mains). You can also sweep round the core with a piece of sheet steel; it should not pick up serious magnetism anywhere.
My guess is rather that 50 Hz 'strikes' the mechanical resonance of a loose lamination. If this proves to be the case, some serious investigation might be required to silence it. Open up and try all manner of pressure everywhere, also jamming something thin between winding bobbin and laminations; a table knife or whatever - with the necessary safety precaution for shock.
With the core securely clamped (not over-tightened!), it is unlikely that somewhere inside where you have no access, something will be vibrating to a troublesome extent. Examine the core: Are all the "E"s and "I"s in place and properly touching each other?
Etc. When you have located the problem, you can usually pour/squirt some varnish/whatever into the region or some spacer somewhere. I hope you are successful; I occasionally had to use patience, but have always found some form of loose lamination. Don't ignore the shell; that can also vibrate where touching the core!
Follow:
I cannot quite make out the exact nature of the mentioned metal 'clamps' in the photo. What are they clamping? Sometimes in core assemblies the outer "E"s have protruding limbs to hold the outer "I". Are you sure that the clamps are not such? If there is indeed an air gap somewhere between shell and laminations, that can be a recipe for mechanical hum.
I cannot quite make out the exact nature of the mentioned metal 'clamps' in the photo. What are they clamping? Sometimes in core assemblies the outer "E"s have protruding limbs to hold the outer "I". Are you sure that the clamps are not such? If there is indeed an air gap somewhere between shell and laminations, that can be a recipe for mechanical hum.
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