Thanks a lot. I need this to decide how to orient my sockets so the heater wiring doesn't have to go around the socket, and that will determine where I drill the holes for the bolts.
Do people usually cut transformer leads to size, or leave them at their original size? The latter would facilitate reusing the iron in future projects, but would make for messier wiring dress.
Do people usually cut transformer leads to size, or leave them at their original size? The latter would facilitate reusing the iron in future projects, but would make for messier wiring dress.
Cutting transformer leads is all down to how confident you are. I try to route them so that there is enough lead left if they have to be salvaged.
The worst possible thing to do with heater wiring is to wire round the socket on one side with the incoming, and round the other with the outgoing. You've just made a loop aerial with the valve in the middle. If you have to loop round to a tag on the far side, do the incoming and outgoing wires on the same side.
The worst possible thing to do with heater wiring is to wire round the socket on one side with the incoming, and round the other with the outgoing. You've just made a loop aerial with the valve in the middle. If you have to loop round to a tag on the far side, do the incoming and outgoing wires on the same side.
Saurav said:
hi, i guess you've got to make a decision now if you will be re-using your transformer. specially with the 125ESE, i did not cut them because i've used them in 4 different amps already (with positive results on all) with varying physical designs. besides, the wires of the 125ESE are not at all that difficult to coil and have it pinned to the chassis.
my 2 cents
Arnold, I think that's what I'll do to begin with.
I set up the power transformer today, wire-nutted all secondary wires, and tested my OPT with the scope on the primary leads. I got a lot of noise, and finally ended up shorting the OPT outputs, and grounding one of the inputs (the one the probe's ground was connected to). Then I got a consistent reading, and could see the effects of changing transformer orientation. And this is where things got strange. I got the smallest waveform on the scope if the OPT's laminations were oriented the same way as the power transformer's laminations. That's the opposite of everything I've ever read. The waveform also changed shape. It was never a sine wave, it was more like a double triangle/sawtooth kind of a wave.
Since I'm such a smart guy, I had drilled all the holes for the OPTs before I tested this
That's not a biggie though, the holes can be covered and new holes can be drilled. However, I don't understand why the lowest induced noise happened when the laminations of the two transformers were lined up. Are the coils wound differently in the two? I connected one of the 2A3 filament transformers too, just to make sure that that didn't change things. No current was being drawn from either transformer though, and I don't know how much of a difference that will make to radiated electromagnetic fields. I know the heater wires themselves will radiate noise once they're carrying current. And the PS choke isn't connected either, I don't know if that can have as much of an effect as the PS transformer.
Should I wait and build the whole circuit with clip leads and then test for OPT position? I don't know how much hum I'm getting either, my scope has a gain control with no marking s on it, and several stickers saying it's uncalibrated. I should get hold of a reliable signal generator and calibrate my scope. Anyway, it looks like I have anywhere from 5mV to 8mV of hum. If I don't ground the probe lead, that becomes 50mV of very noisy hum.
If anyone can put all of this together and derive any insights from it, that would be really helpful.
Thanks,
Saurav
I set up the power transformer today, wire-nutted all secondary wires, and tested my OPT with the scope on the primary leads. I got a lot of noise, and finally ended up shorting the OPT outputs, and grounding one of the inputs (the one the probe's ground was connected to). Then I got a consistent reading, and could see the effects of changing transformer orientation. And this is where things got strange. I got the smallest waveform on the scope if the OPT's laminations were oriented the same way as the power transformer's laminations. That's the opposite of everything I've ever read. The waveform also changed shape. It was never a sine wave, it was more like a double triangle/sawtooth kind of a wave.
Since I'm such a smart guy, I had drilled all the holes for the OPTs before I tested this
That's not a biggie though, the holes can be covered and new holes can be drilled. However, I don't understand why the lowest induced noise happened when the laminations of the two transformers were lined up. Are the coils wound differently in the two? I connected one of the 2A3 filament transformers too, just to make sure that that didn't change things. No current was being drawn from either transformer though, and I don't know how much of a difference that will make to radiated electromagnetic fields. I know the heater wires themselves will radiate noise once they're carrying current. And the PS choke isn't connected either, I don't know if that can have as much of an effect as the PS transformer.Should I wait and build the whole circuit with clip leads and then test for OPT position? I don't know how much hum I'm getting either, my scope has a gain control with no marking s on it, and several stickers saying it's uncalibrated. I should get hold of a reliable signal generator and calibrate my scope. Anyway, it looks like I have anywhere from 5mV to 8mV of hum. If I don't ground the probe lead, that becomes 50mV of very noisy hum.
If anyone can put all of this together and derive any insights from it, that would be really helpful.
Thanks,
Saurav
Saurav,
Two things to say about the choke placement:
The choke can recieve field from the mains transformer. With full wave or bridge rectification, this is always destructive to performance. It's got to be be very close and in-line for this to happen.
The choke can transmit field to the audio transformers. This is usually destructive, but can sometimes be constructive, and reduce other hum.
Bottom line: Bolt down the choke last.
Cheers,
Two things to say about the choke placement:
The choke can recieve field from the mains transformer. With full wave or bridge rectification, this is always destructive to performance. It's got to be be very close and in-line for this to happen.
The choke can transmit field to the audio transformers. This is usually destructive, but can sometimes be constructive, and reduce other hum.
Bottom line: Bolt down the choke last.
Cheers,
Shorting the OPT outputs will definitely produce odd results! Perhaps you need to earth the chassis of the output transformer and the mains transformer. When you do this test, you should see a nice clean sine wave, with maximum amplitude when the coils are aligned, and far less at the null.
Your oscilloscope sounds very strange. It doesn't need to be calibrated, all you're looking for is a minimum.
Your oscilloscope sounds very strange. It doesn't need to be calibrated, all you're looking for is a minimum.
I was thinking about this last night, and I think I know what might have happened. When I connected the IEC power socket, I only used the hot and cold terminals and hooked up the PS trafo to those, I did not connect the earth terminal to the chassis. So, my aluminum chassis was floating, and so were the frames of the transformers sitting on it. By connecting the probe ground clip to the chassis (and one of the OPT's leads), what I did was ground my chassis, and the transformers sitting on the chassis, which probably helped clean up the signal.
Potentially dumb question - are the coils aligned when the laminations are aligned? Or can coils be wound/oriented differently w.r.t. the laminations?
I'll try it again with the OPT outputs unshorted. I definitely did not get a sine wave. I got a triangular wave with one large triangle and one small triangle, which changed shape and amplitude as I turned the OPT.
And my power transformer is humming. I can't feel it vibrating when I touch it, but I can hear it. It'll probably get worse once I start drawing current through it, right? I'll probably go ahead and mount it on grommets and use a ring connector to earth it.
It's a Tek (forget the model #) 100MHz scope that I picked up for $75 from a local surplus store. 1 timebase unit and 2 dual channel amplifiers included. Pretty good deal, I thought
That's what I figured when I bought it.
John,
Thanks for the advice. I'll keep an eye on the choke's effects.
Since it's all 60Hz, can the hum balance pot be adjusted to cancel out electromagnetically induced hum? I know it's meant to balance the filament transformer to be symmetrical around ground, but can it be used after everything's been put together to just minimise the final hum from all sources? I know that's a bandaid, but I'm just wondering if it'll have any effect.
Potentially dumb question - are the coils aligned when the laminations are aligned? Or can coils be wound/oriented differently w.r.t. the laminations?
I'll try it again with the OPT outputs unshorted. I definitely did not get a sine wave. I got a triangular wave with one large triangle and one small triangle, which changed shape and amplitude as I turned the OPT.
And my power transformer is humming. I can't feel it vibrating when I touch it, but I can hear it. It'll probably get worse once I start drawing current through it, right? I'll probably go ahead and mount it on grommets and use a ring connector to earth it.
It's a Tek (forget the model #) 100MHz scope that I picked up for $75 from a local surplus store. 1 timebase unit and 2 dual channel amplifiers included. Pretty good deal, I thought
That's what I figured when I bought it.
John,
Thanks for the advice. I'll keep an eye on the choke's effects.
Since it's all 60Hz, can the hum balance pot be adjusted to cancel out electromagnetically induced hum? I know it's meant to balance the filament transformer to be symmetrical around ground, but can it be used after everything's been put together to just minimise the final hum from all sources? I know that's a bandaid, but I'm just wondering if it'll have any effect.
Coils are not necessarily aligned when laminations are aligned. One coil could be pointing horizontally, and the other vertically (like your output transformers). You should get quite a large signal coupled from a mains transformer into an output transformer when the coils are aligned, perhaps even a volt.
The Tek sounds like a 7000 series. They had very nice tubes with excellent focus. Don't worry about "uncalibrated" labels on oscilloscopes. Oscilloscopes aren't really for measuring, they're for looking at shapes. Try looking your 'scope up on the web. Old Teks are very popular with engineers, some people even collect them!
The Tek sounds like a 7000 series. They had very nice tubes with excellent focus. Don't worry about "uncalibrated" labels on oscilloscopes. Oscilloscopes aren't really for measuring, they're for looking at shapes. Try looking your 'scope up on the web. Old Teks are very popular with engineers, some people even collect them!
Why would the heater be 120Hz? It's direct AC from the filament transformer, not rectified. Or does the fact that it's "center tapped" through the cathode bias resistor make it 120Hz? I understand that the choke field is 120Hz.
So that would be if I laid the OPT on its side? I'll try that, at least that way I'll have some idea that I'm on the right track
I did, and I think I looked up user manuals for the plugin modules on it too. I just don't remember the model number off the top of my head.
So that would be if I laid the OPT on its side? I'll try that, at least that way I'll have some idea that I'm on the right track
I did, and I think I looked up user manuals for the plugin modules on it too. I just don't remember the model number off the top of my head.
I should have made clear that the hum pot will null out 60Hz, but there are 120 heating cycles per second. That's where my 120Hz comes in, and that's what you'll have left.Saurav said:Why would the heater be 120Hz? It's direct AC from the filament transformer, not rectified. Or does the fact that it's "center tapped" through the cathode bias resistor make it 120Hz? I understand that the choke field is 120Hz.
So that would be if I laid the OPT on its side? I'll try that, at least that way I'll have some idea that I'm on the right track
I did, and I think I looked up user manuals for the plugin modules on it too. I just don't remember the model number off the top of my head.
WRT orientation: Most stand-up output and mains transformers are wound so that the windings go up and over. that means they can be orientated at 90 deg just by turning one 90deg, looking from the top. It is then possible to orientate the choke so that it's windings are circular, looking from the top. Thus you can have 3 planes.
A very difficult concept to put into words (for me anyway
) )Cheers,
Saurav said:
The hum comes from the changing AC being partly tracked by the temperature of the filament. Heat doesn't know about positive and negative half-cycles, it just responds to peaks, so it effectively rectifies the AC. (More technically, P = V squared over R, and cos(2A) = 2cos squared(A) -1)
Edit: Calling Planet 10. Is there any way of writing equations so that they make sense?
Math symbols and Greek
EC8010,
Why not write it out in whatever program you have, and then use a screen area capture prog to make a .gif file. You can then attach it as a picture.
I think we are severely limited in the html world, in terms of what can be transmitted. It would take some Java or suchlike to actually generate it locally.
Cheers,
EC8010,
Why not write it out in whatever program you have, and then use a screen area capture prog to make a .gif file. You can then attach it as a picture.
I think we are severely limited in the html world, in terms of what can be transmitted. It would take some Java or suchlike to actually generate it locally.
Cheers,
Doing OK so far...
I liked the copper and black look of PassFan's amp, so I decided to try some copper metallic paint. This is definitely my weakest area, painting metal. I always get blotches on there with spray paint, and sometimes the paint doesn't stick. You can kinda tell from these pictures, the paint's "peeled" off in a few places, and it's pretty uneven. Maybe I'm using the wrong kind of primer, I don't know.
Anyway... I'll probably start on the wiring tomorrow, and maybe take pictures of the underside.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I liked the copper and black look of PassFan's amp, so I decided to try some copper metallic paint. This is definitely my weakest area, painting metal. I always get blotches on there with spray paint, and sometimes the paint doesn't stick. You can kinda tell from these pictures, the paint's "peeled" off in a few places, and it's pretty uneven. Maybe I'm using the wrong kind of primer, I don't know.
Anyway... I'll probably start on the wiring tomorrow, and maybe take pictures of the underside.
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