| JBLoudg20 |
Hey all,
I have been working on my latest project, and right off the bat Ihave hit a snag. I am using a Hammond 183K12 to power the heaters of 2 6AS7G and 2 6SN7. I Connetect the transformer as follows: (the bottom transformer is my Hammond 269AX for the PSU section)
When I turned on the power, the transformer started smoking, and I quickly cut power. I disconnected everything from the secondaries, and turned it back on to test the voltage, and unfortunately I got zero. I have ordered another transformer, but I'd like to knwo what I did wrong. I am about 99.9% sure I wired it as shown by my drawing.
Any ideas? Thanks in advance. |
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| jleaman |
| quote: | Originally posted by JBLoudg20
Hey all,
I have been working on my latest project, and right off the bat Ihave hit a snag. I am using a Hammond 183K12 to power the heaters of 2 6AS7G and 2 6SN7. I Connetect the transformer as follows: (the bottom transformer is my Hammond 269AX for the PSU section)
When I turned on the power, the transformer started smoking, and I quickly cut power. I disconnected everything from the secondaries, and turned it back on to test the voltage, and unfortunately I got zero. I have ordered another transformer, but I'd like to knwo what I did wrong. I am about 99.9% sure I wired it as shown by my drawing.
Any ideas? Thanks in advance. |
What is the brand what does it look like ? Maybe you can request a drawing diagram to connect it to the ac voltages you need.. I have seen some people buy a 110V ac tranny and use 220 buy mistake. We can help you if you can provide details of make model etc etc :) |
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| anatech |
Hi jleaman,| quote: | | I am using a Hammond 183K12 to power the heaters of 2 6AS7G and 2 6SN7. |
JBLoudg20,
Your diagram is okay. How fast did you say it smoked? I assume you did check the heater currents against the Hammond's ratings. I haven't yet. You always leave some headroom there.
But even still, I've not seen a transformer smoke quickly unless it's high current and the winding is shorted. The hum would tip you off first I'd think.
-Chris |
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| jackinnj |
| i have been doin' this for 40+ years and have never made a trannie smoke -- even through the thick and thin of many catastrophes in audio, ham radio and physics labs which destroyed several transformers (I burned out the transformer in my Eico 753 Tri-Band transceiver when I keyed down on 20 meters for too long -- rewound the transformer !) |
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| tubelab.com |
If you accidentally wire the two parallelled primaries so they are out of phase, the transformer will smoke immediately! Don't ask me how I know this. If the power wasn't on long, there may still be some life left in it. I woudn't use it in an amp, but I would try again before you smoke the new one.
If you look at the diagram on Hammonds web page you will see a small dot next to one of the pins on each winding. Whenever two windings are connected in parallel the pins with the dots are connected to each other, and the pins without the dots are connected to each other. For this transformer, connect pins 1 and 4 together. Connect 3 and 6 together. Connect power to the 1-4 pair and to the 3-6 power. Test for voltage with no load. If you have voltage, then try it with a load. |
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| jleaman |
| quote: | Originally posted by tubelab.com
If you accidentally wire the two parallelled primaries so they are out of phase, the transformer will smoke immediately! Don't ask me how I know this. If the power wasn't on long, there may still be some life left in it. I woudn't use it in an amp, but I would try again before you smoke the new one.
If you look at the diagram on Hammonds web page you will see a small dot next to one of the pins on each winding. Whenever two windings are connected in parallel the pins with the dots are connected to each other, and the pins without the dots are connected to each other. For this transformer, connect pins 1 and 4 together. Connect 3 and 6 together. Connect power to the 1-4 pair and to the 3-6 power. Test for voltage with no load. If you have voltage, then try it with a load. |
Id also try it with a variac too. Power it up slowly |
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| JBLoudg20 |
| quote: | Originally posted by anatech
Hi jleaman,
JBLoudg20,
Your diagram is okay. How fast did you say it smoked? I assume you did check the heater currents against the Hammond's ratings. I haven't yet. You always leave some headroom there.
But even still, I've not seen a transformer smoke quickly unless it's high current and the winding is shorted. The hum would tip you off first I'd think.
-Chris |
It didn't hum at all, which I thought was strange. The transformer is rated at 8.8A, and mt tubes should draw about 6A of current, so I should be ok there.
| quote: | Originally posted by tubelab.com
If you accidentally wire the two parallelled primaries so they are out of phase, the transformer will smoke immediately! Don't ask me how I know this. If the power wasn't on long, there may still be some life left in it. I woudn't use it in an amp, but I would try again before you smoke the new one.
If you look at the diagram on Hammonds web page you will see a small dot next to one of the pins on each winding. Whenever two windings are connected in parallel the pins with the dots are connected to each other, and the pins without the dots are connected to each other. For this transformer, connect pins 1 and 4 together. Connect 3 and 6 together. Connect power to the 1-4 pair and to the 3-6 power. Test for voltage with no load. If you have voltage, then try it with a load. |
Well, I may actually have made a mistake then. I ran jumper wires from one 6AS7G to one 6SN7. I then did the same thing wit the other set of tubes. Then I ran one winding of the secondary to one of the sets, and the other winding to the other set. However, the windings were never run to each other, so I doubt they were out of phase. |
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| jamesjung21 |
| quote: | | If you look at the diagram on Hammonds web page you will see a small dot next to one of the pins on each winding. |
How about in the case when I have to connet them in series..? Does it really matter which way I connect them together (do I have to connect the dotted pins together and use the two un-dotted pins for primary input...?)
The dots are also present on some vintage potted HP transformers...
Thanks,
James |
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| SY |
| quote: | | Does it really matter which way I connect them together in series..? |
Yes. |
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| jamesjung21 |
So, does that mean I have to connect the dotted pins together and use the two un-dotted pins for mains input...? |
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| Jeb-D. |
Tubelab is right. If the primaries are out of phase, they will cancel the inductive reactance. The DC resistance of the windings will be the only resistance in the circuit. Causing it to draw way too much current. See this page
http://www.hammondmfg.com/5CHook.htm
The Second example for the primaries is what your trying to do.
My only guess is you connected 2&3 togeather then 1&4 together. Which is bad. If you didn't do that, then I can't see why you fried it. It should be capable of supplying the heater for those tubes. |
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| Miles Prower |
| quote: | Originally posted by jamesjung21
So, does that mean I have to connect the dotted pins together and use the two un-dotted pins for mains input...? |
Not for a series connection. For a series connection, it's dotted-to-undotted to form a center tap, and mains connection to the remaining dotted and undotted terminals. Of course, if you get it wrong with a series connection, you get little voltage. Reverse phase in a parallel connection, and you poof something. |
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| Makofoed-6sn7 |
Hi,
I don't think we can stress enough about the phase of the windings in a transformer.
I have made the mistake with conecting the windigs so that they cancel each other. I always test an amplifier on a variac. Some times you think you have it all right, but again...
Hammond is very nice with that they always supplies a diagram for how you should conect the wires for different operations of the transformer.
I remeber one episode at work when I changed an transfomer. I did a mistake and the current drawn was so big that the main fuse for the workbench did blow! Wonders of wonder the fuse in the amplifier did hold. Mysterious things.
Regards,
Magnus |
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| jamesjung21 |
| quote: | | Hammond is very nice with that they always supplies a diagram for how you should conect the wires for different operations of the transformer. |
Is this phenomenon applicable only on certain transformers with double primary windings, or is it applicable to all transformers with double primary windings...?
If this happens with all, is there a trick for figuring out the direction when directions are not indicated...? |
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| anatech |
Hi jamesjung21,
This happens with all dual voltage transformers (dual primary). The same will occur when hooking secondaries together (I don't recommend this) to increase current capacity. Even if they transformers are different but identical units.
-Chris |
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| tubelab.com |
ANY time you connect multiple windings in series or parallel on transformers you must get the phasing right. I believe Miles is right about the series case. Getting it wrong will give you no voltage but no smoke. Since 240 volts is not common here, I have never tested that theory though.
A new transformer should be marked in some manner. There should be a diagram that matches the wire colors to the correct hookup.
If you are dealing with an undocumented transformer, I use the light bulb method:
Take your best guess as to how to connect it. Connect a light bulb (same voltage as your power source) in series with the power source. The bulb should be of a small enough wattage to limit the current in the transformer to a safe value. For power transformers of the size typically found in tube amplifiers, I use a 75 watt 120 volt bulb. I would use a smaller bulb for a filament transformer (40 watt). With NO load on the transformer, apply power, the bulb should not light up (or glow very dimly). The secondary voltages should be close to the expected values. If the bulb lights up brightly, the transformer is wired up incorrectly, or it is bad. If there is a wiring error the energy is used to light the bulb instead of making smoke!
I use this method to test any flea market transformer. I sometimes use it with a Variac to figure out what voltages are present on undocumented transformers. I have several light bulbs in sizes form 25 watts, to 500 watts. I use these in series with the mains voltage to power up any old, or unknown electronic equipment.
I believe that of the solid state amplifier kit manufacturers (Dynaco, Heathkit ?) pioneered this method back in the 1960's. I have been using it ever since. |
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| JBLoudg20 |
| I just checked, and I had pins 1&6 together, and pins 3&4 together. Secondaries: I had pins 9&7 out to one heater, and 12&10 out to the other heater. |
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| JBLoudg20 |
And of course, I wired it incorrectly. Looks like I had the primaries out of phase.
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| anatech |
Hi JBLoudg20,
Yup, that will do it every time. Sorry to hear about that.
-Chris |
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| kevinkr |
:hot: :hot: :hot: :hot:
For 240V operation connecting two windings in series out of phase will get you lots of smoke! (Particularly if you don't use a fuse of suitable rating.)
Just as is the case with an incorrectly phased parallel connection the winding inductance will cancel as a function of the windings mutual inductance (coupling) leaving you with very little more than just the DCR. (And some inconsequential leakage inductance as well.)
You can easily model this error in most circuit simulation software.
Incidentally if you don't own a variac (and even if you do) a ballast lamp temporarily inserted in series with the primary windings will prevent damage to the transformer should you get the phasing wrong for either connection. Something like a 25W - 100W incandescent bulb (or more) at your local line voltage will provide adequate protection depending on the rating of your transformer. |
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| Miles Prower |
| quote: | Originally posted by kevinkr
:hot: :hot: :hot: :hot:
For 240V operation connecting two windings in series out of phase will get you lots of smoke! (Particularly if you don't use a fuse of suitable rating.)
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On the primary side with two 120V pri's in series, it would. Out of phase series secondaries simply cancel and give very little voltage. Of course, it is NBD to connect a light bulb in series with anything when giving it the first power on test. On a couple of occasions, doing this very thing has saved me some serious poofage.
That's another reason why I favor separate heater and plate supplies: you can light up the heaters while limiting current to the HV supply. |
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| kevinkr |
I was specifically addressing the issues of primary connections, but probably should have clarified further.
Connecting two primaries out of phase cancels out their inductance whether they are connected in series or parallel with each other. What you are left with in both cases is the dcr of the windings in series or parallel as the case may be.
Connecting secondaries in parallel out of phase, same deal as with the primaries in parallel, in series fortunately they just cancel.
I have done quite a lot of work with transformers operating on both 120V and 240V. Have first hand experience. I use Hammond 3XX dual primary power transformers in most of my current projects.
Growing up overseas I replaced several dual primary transformers that inexperienced DIY'ers had series connected for 240V operation, but unfortunately out of phase. Yes they smoked, and I could still smell it when I worked on them. In no case were there wiring errors on the secondary side that would have resulted in the near instant destruction of the transformer. |
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| anatech |
Hi Kevin,
Now there's a smell you will never forget! ;)
-Chris |
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| JBLoudg20 |
| I'm chalking this one up to experience, and a valuable lesson learned. At least I fried my $25 tranny and not a more expensive one. |
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| anatech |
Hi JBLoudg20,
That's what I was thinking, but I didn't have the heart to say it. It was a relatively inexpensive lesson.
You'll get to my age and still remember it. ;)
-Chris |
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