Hi all,
I've some power transformers from an old radar test set with a lot of windings for building a nice tube amp.
Unfortunatly these are 110V unit and here in Belgium we have 220 (230V) mains.
What if I used one transformer for each stereo channel and connect the primairies in series ??
This should work as both transformers have the same load or am I wrong ???
Or shall I by a beefy 220/110 autoformer ??
Thanks,
Jim
I've some power transformers from an old radar test set with a lot of windings for building a nice tube amp.
Unfortunatly these are 110V unit and here in Belgium we have 220 (230V) mains.
What if I used one transformer for each stereo channel and connect the primairies in series ??
This should work as both transformers have the same load or am I wrong ???
Or shall I by a beefy 220/110 autoformer ??
Thanks,
Jim
But in practise this is very rarely so.
Even a temporary imbalance in the loads will shift voltages a lot, and if the loads are non-linear (eg tube filaments and tubes in general during warm-up, as well as implemented in some circuits), you will have a bunch of strange effects.
But things can be helped if you have two transformers with identical primaries and at least one identical secondary winding, preferably separated from the other windings, and preferably a winding with the highest power rating (even if you are not going to use that power in your aplication). You can connect the primaries in series and the identical secondary windings in parallel (CAREFUL! not anti-paralel or you will create a short). The parallel connected windings will normally share current as long as the load on both transformers is the same. If the load is different, the parallel connected windings will act as a balnce winding, and will pass any differential currents from one to another, thereby balancing the load on the transformers.
A filament winding would be a good candidate for parallel connection, as it is generally the most beefy one.
Other arrangements are possible. One thing you must be careful about is not to load one transofrmer during one mains half-period and the other during the other half-period. You get DC magnetisation that way, which gap-less transformers, and mains transformers are of that type, do not like because of core saturation. At the very least you will get hugely increased hum and quite probably 'inexplicable' winding heat up.
Even a temporary imbalance in the loads will shift voltages a lot, and if the loads are non-linear (eg tube filaments and tubes in general during warm-up, as well as implemented in some circuits), you will have a bunch of strange effects.
But things can be helped if you have two transformers with identical primaries and at least one identical secondary winding, preferably separated from the other windings, and preferably a winding with the highest power rating (even if you are not going to use that power in your aplication). You can connect the primaries in series and the identical secondary windings in parallel (CAREFUL! not anti-paralel or you will create a short). The parallel connected windings will normally share current as long as the load on both transformers is the same. If the load is different, the parallel connected windings will act as a balnce winding, and will pass any differential currents from one to another, thereby balancing the load on the transformers.
A filament winding would be a good candidate for parallel connection, as it is generally the most beefy one.
Other arrangements are possible. One thing you must be careful about is not to load one transofrmer during one mains half-period and the other during the other half-period. You get DC magnetisation that way, which gap-less transformers, and mains transformers are of that type, do not like because of core saturation. At the very least you will get hugely increased hum and quite probably 'inexplicable' winding heat up.
Luminous idea !
As far as I remenber, Philps did something like that on their latest tubed color TV set.
They had two multiple winding bobins on a singe dual C core.
They tied ALL indentical secondaries in paralell, while primary were serie or paralell connected according the main voltage.
This should work even with two trannies, providing they are STRICLY identical.
The result is like a single tranny with twice the rating of each.
Check with a light bubble in serie with primaries !
Be cautious, Yves.
ilimzn said:
As far as I remenber, Philps did something like that on their latest tubed color TV set.
They had two multiple winding bobins on a singe dual C core.
They tied ALL indentical secondaries in paralell, while primary were serie or paralell connected according the main voltage.
This should work even with two trannies, providing they are STRICLY identical.
The result is like a single tranny with twice the rating of each.
Check with a light bubble in serie with primaries !
Be cautious, Yves.
Very doable!
O.K As explained already, this is very doable and I do it all the time with good quality transformers as the ones used in radars and other military equipment.
You can in fact wire the primaries in series and then all the identical secondaries in parallel one by one, not all together in one try! You only have to wire a common 60W valve in series with the primary. When the light bulb glows means you attatched the wrong secondary polarity. So you reverse this and continue to the next.
Its fairly easy to do and safe. I do it very often as my local scrapyard mainly got 110 primaries transformers, but you can get many pairs cheap. Most of the times these old "crappy" poted transformers are of super quality compared with modern ones and all the times the 6,3V winding is exactly 6,3, ven fully loaded.
Do not forget to unplug the mains when you solder the secondaries!!!!!!
Good luck!
O.K As explained already, this is very doable and I do it all the time with good quality transformers as the ones used in radars and other military equipment.
You can in fact wire the primaries in series and then all the identical secondaries in parallel one by one, not all together in one try! You only have to wire a common 60W valve in series with the primary. When the light bulb glows means you attatched the wrong secondary polarity. So you reverse this and continue to the next.
Its fairly easy to do and safe. I do it very often as my local scrapyard mainly got 110 primaries transformers, but you can get many pairs cheap. Most of the times these old "crappy" poted transformers are of super quality compared with modern ones and all the times the 6,3V winding is exactly 6,3, ven fully loaded.
Do not forget to unplug the mains when you solder the secondaries!!!!!!
Good luck!
Perhaps I missed something, he says he wants to use one for each channel in stereo mode. If so, he cannot do it. In a stereo set-up each channel cannot be assumed to be operating at the same load levels thus a mismatch in power/ load will cause a voltage drop in one transformer and increase of voltage in the other.... this will not be good for the amp.....
K-amps said:
If he has the heater windings of both tied together in parallel, the two transformers will exchange current to equalize things out. Also the filtering of the two unit's power supplies should smooth over the transient imbalances of the loading caused by the music.
I was going to mention strapping both high voltage secondaries together as well, but if the turns ratios are even slightly different between the two transformers, you could smoke the transformers (shorted turn effect). Also you wouldn't want 300VAC wiring between the two chassises, shock hazard.
bocka said:
Should I point out that military grade transformers are made under stricter rules than DIN EN or VDE, which is something you would have noticed if you had read the thread from the start. MILS STD are definitely NOT wound to the limi of saturation, quite the oposite, the specs given are usually very conservative.
I have read the thread from start.
The question is not if it works but if its safe and if it legally allowed. The standards are IEC-61558 or IEC-60742. When you connect a transformator to the mains which is driven out of its specs and something hazardous occurs that one who has connected the transformator to the mains is fully responsible for its consequences. Is this really worth it?
bocka said:
This could be said for any DIY project - especially one with second-hand components, for which there are no guarantees that they will work, and even if they do, they are certainly not made under the mentioned standards.
As always with such projects, you make your choices, you take your chances and you have to accept the consequences.
I know what you are trying to say but this sort of legislative reasoning is preposterous in the context of tis forum or indeed in the context of engineering. Specs are not a dogma. They are made under certain conditions and when the conditions change, you may still get a completely functional and safe design BUT working at different specs. The key word of course is 'may' and there is no voodo involved, but just simple principles.
According to your post, people who for instance use mains toroids as PP output transformers may well expect armageddon because those were not how they were originally specced.
Having been involved with mil spec design and testing for 7 years, I have not typed my answers out of thin air. Even so, since the original author of the thread is working with second hand equipment, it would be quite unwise to just take all of our collective words on faith - the answer, as usual is, once you have ascertained that the given mode of operation may be well inside the specs, you test things under controlled conditions. No one is saying he should jus connect the transformers blindly and then sue us all if his house burns down. Besides, there is always a chance that could happen even if they were IEC-61558 or IEC-60742 certifie. In fact, I would trust second hand mil stuff dug out of a trash-heap that got flattened by a bulldozer more than some brand new parts you can buy that apparently have all the necessary certification (I'm not going to mention countries of origin here)...
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