I'm in the process of testing the OT and PT from the organ amp I salvaged.
I just tested the OT in the manner described here: http://www.diyguitarist.com/GuitarAmps/ ... edLoad.htm
Putting wall AC across the primaries I read 2.5v AC on the secondaries. According to the chart it should give me 8.4k/4ohms, or 16.9k/8 ohms. Does that math sound right? If it is right, what is this useable for?
More to come on the PT.
EDIT:
Here's what I got for the PT
Red - 594 VAC, 295 to center tap
Green 35 VAC, 17.3 VAC to CT
Yellow 5.2 VAC
Orange 6.6 VAC
What can I do with this mofo? Are there more tests I should do? I guess I don't know current ratings on it and am not sure how to test them.
Transformer Testing
Moderators: pompeiisneaks, Colossal
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Sonny ReVerb
- Posts: 342
- Joined: Sun Feb 05, 2006 6:54 pm
Re: Transformer Testing
I had a similar problem when I used salvaged trannies for a 6AQ5 build. The PT (red wires) will give you around 400VDC (295x1.35) with a tube recto or a little more using diodes. Not sure what you could use the green (35VAC) wires for. The yellow (5VAC) are for a tube recto. The orange (6.3VAC) are for the filaments or heaters. (You probably knew some of this.)
The main problem I found was determining current handling. From what I've read, that's determined by core size and wire diameter. Not easy to calculate from a tranny in hand. If you know the tube complement of the organ that the PT was used with, you can add up the heater ratings of the various tubes to get an estimate of heater current available. Otherwise, my best advice would be to try it in your desired circuit and see how warm it gets. A rough rule of thumb I've heard is if you can keep your hand on it, it's not too hot. YMMV
The OT, with 8k at 4 ohms, would be good for a pair of 6V6's or EL84's into a pair of 8 ohm speakers in parallel. Maybe someone else can chime in with other suggestions.
The main problem I found was determining current handling. From what I've read, that's determined by core size and wire diameter. Not easy to calculate from a tranny in hand. If you know the tube complement of the organ that the PT was used with, you can add up the heater ratings of the various tubes to get an estimate of heater current available. Otherwise, my best advice would be to try it in your desired circuit and see how warm it gets. A rough rule of thumb I've heard is if you can keep your hand on it, it's not too hot. YMMV
The OT, with 8k at 4 ohms, would be good for a pair of 6V6's or EL84's into a pair of 8 ohm speakers in parallel. Maybe someone else can chime in with other suggestions.
Re: Transformer Testing
Testing an unknown PT is a whole can of worms, as there is a lot going on and it is necessary to consider all of the windings, not just the high voltage secondary. I've just been through this question elsewhere an got a pile of good advice, which I will try to summarize.
Ohm's law is your friend. You will apply it over and over, so I won't cover that. Just get it and learn it.
A PT has a VA rating. This rating is the maximum load of all secondaries taken together. Remember, they all pull from a single primary coil.
From this point forward, I'm only going to discuss the high voltage winding and ingnore the rest. Remember, you can't really do that, so some allowance will need to be made in the end.
It is not practical to test a PT for maximum load. The only way you know for sure is to burn it up or to unwind it. Either way, you destroy it. So, test it for intended use and see if it is up to the job.
Get an temerature probe. Put a load on the secondary and see how hot the PT gets. A reasonable maximum is the boiling point of water 212F or 100C. Hotter than that is too hot. This is something you do over a period of a couple of hours.
Do some math. I do well with examples, so let me tell you about my unknown PT. Unloaded, the secondary is 327-0-327. With 14.7K load (10W 15K wirewound) it puts out 643vac across the outer legs; 9.8K 640v; 5.8K 634v. What does this tell us? Ohm's law at work...
14.7k 643v 44mA 28W
9.8k 640v 65mA 42W
5.8k 634v 109mA 69W
Taking a guess that the loaded output should be about 95% or 96% of unloaded, 327-0-327 (or 655v) should perform at about 310-0-310. So, to get a proper test going on here, we know from the above math that I need a much more robust load than a 10W wirewound resistor. I probably need a 100W rated load. The above data are on a curved line and a bit too close together to get a good read off a graph. I am guessing that a load of about 3.3K will give me 620v. Let's just assume for discussion that I'm right. So:
3.3K 620v 188mA 116W
What I should do here is build a 100W rated load at around 4K and keep track of the temperature for about 2 hours. Then, slowly reduce the load until the temperature rises to around the 212F. Then, I pretty much know what the safe load is for this PT.
You can test the other windings in similar fashion. Given the low voltage and higher amp rating on filament windings, adjust all tests accordingly. I would not try to test filament windings for maximum. In some respects, testing for filament capacity is easier. Build a test rig with a bunch of tube sockets wiring only the filaments. Keep plugging in tubes until your output drops to 6.3v or close to it and then you will know the capacity. You can probably push the envelope down to around 6.1v without a risk to the tubes, but then you must reconsider in terms of the overall VA rating of the PT, that you are not demanding more of the primary than it can produce. The same is true on the 5V winding, except there you really only need one socket and a few tubes. For example a 5U4 needs 5v @ 1.2A and a 5Y3 needs 5V @ 2.0A.
You have a 35v winding. Assuming it is for bias supply, that typically is a very low current draw. I would probably not bother to test it much.
We aren't done yet. There are determinations that can also be made based on the resistance of the windings. Put an ohm meter on it and use this lookup table (someone gave this to me and I can't assert it is reliable because I don't know it's true origin):
From the Primary Winding:
For a 120 volt AC supply the VA rating and primary resistance is as
folows.
30 VA = 30 to 40 ohms
50 VA = 13 to 16 ohms
80 VA = 7 to 9 ohms
120 VA = 5 to 6 ohms
160 VA = 2.5 to 3.5 ohms
225 VA = 1.8 to 2.2 ohms
300 VA = 1.0 to 1.3 ohms
500 VA = 0.45 to 0.55 ohms
Simply multiply all ohm values by four (4) for a 230/240 volt supply.
Derate to 65%, which is probably reasonable and to allow 15VA for the filament windings.
From the Secondary Winding:
One very general way, based on a copper loss of say 4%. The ht winding rating is probably the most important. Find the secondary voltage, e.g. 300Vac. Take 4%, giving 12V. Measure the winding resistance; one half if 300-0-300V (i.e. a 300V winding), if bridge then the whole winding. The current will now be that which causes a 12V drop across the winding d.c. resistance. Thus dividing 300V by the resistance would give a ball-park figure for current (Ohms Law).
Ohm's law is your friend. You will apply it over and over, so I won't cover that. Just get it and learn it.
A PT has a VA rating. This rating is the maximum load of all secondaries taken together. Remember, they all pull from a single primary coil.
From this point forward, I'm only going to discuss the high voltage winding and ingnore the rest. Remember, you can't really do that, so some allowance will need to be made in the end.
It is not practical to test a PT for maximum load. The only way you know for sure is to burn it up or to unwind it. Either way, you destroy it. So, test it for intended use and see if it is up to the job.
Get an temerature probe. Put a load on the secondary and see how hot the PT gets. A reasonable maximum is the boiling point of water 212F or 100C. Hotter than that is too hot. This is something you do over a period of a couple of hours.
Do some math. I do well with examples, so let me tell you about my unknown PT. Unloaded, the secondary is 327-0-327. With 14.7K load (10W 15K wirewound) it puts out 643vac across the outer legs; 9.8K 640v; 5.8K 634v. What does this tell us? Ohm's law at work...
14.7k 643v 44mA 28W
9.8k 640v 65mA 42W
5.8k 634v 109mA 69W
Taking a guess that the loaded output should be about 95% or 96% of unloaded, 327-0-327 (or 655v) should perform at about 310-0-310. So, to get a proper test going on here, we know from the above math that I need a much more robust load than a 10W wirewound resistor. I probably need a 100W rated load. The above data are on a curved line and a bit too close together to get a good read off a graph. I am guessing that a load of about 3.3K will give me 620v. Let's just assume for discussion that I'm right. So:
3.3K 620v 188mA 116W
What I should do here is build a 100W rated load at around 4K and keep track of the temperature for about 2 hours. Then, slowly reduce the load until the temperature rises to around the 212F. Then, I pretty much know what the safe load is for this PT.
You can test the other windings in similar fashion. Given the low voltage and higher amp rating on filament windings, adjust all tests accordingly. I would not try to test filament windings for maximum. In some respects, testing for filament capacity is easier. Build a test rig with a bunch of tube sockets wiring only the filaments. Keep plugging in tubes until your output drops to 6.3v or close to it and then you will know the capacity. You can probably push the envelope down to around 6.1v without a risk to the tubes, but then you must reconsider in terms of the overall VA rating of the PT, that you are not demanding more of the primary than it can produce. The same is true on the 5V winding, except there you really only need one socket and a few tubes. For example a 5U4 needs 5v @ 1.2A and a 5Y3 needs 5V @ 2.0A.
You have a 35v winding. Assuming it is for bias supply, that typically is a very low current draw. I would probably not bother to test it much.
We aren't done yet. There are determinations that can also be made based on the resistance of the windings. Put an ohm meter on it and use this lookup table (someone gave this to me and I can't assert it is reliable because I don't know it's true origin):
From the Primary Winding:
For a 120 volt AC supply the VA rating and primary resistance is as
folows.
30 VA = 30 to 40 ohms
50 VA = 13 to 16 ohms
80 VA = 7 to 9 ohms
120 VA = 5 to 6 ohms
160 VA = 2.5 to 3.5 ohms
225 VA = 1.8 to 2.2 ohms
300 VA = 1.0 to 1.3 ohms
500 VA = 0.45 to 0.55 ohms
Simply multiply all ohm values by four (4) for a 230/240 volt supply.
Derate to 65%, which is probably reasonable and to allow 15VA for the filament windings.
From the Secondary Winding:
One very general way, based on a copper loss of say 4%. The ht winding rating is probably the most important. Find the secondary voltage, e.g. 300Vac. Take 4%, giving 12V. Measure the winding resistance; one half if 300-0-300V (i.e. a 300V winding), if bridge then the whole winding. The current will now be that which causes a 12V drop across the winding d.c. resistance. Thus dividing 300V by the resistance would give a ball-park figure for current (Ohms Law).
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tele_player
- Posts: 311
- Joined: Sat Sep 29, 2007 3:27 am
Re: Transformer Testing
That's a pretty nice explanation, and underscores my feeling that it's not worth the effort to salvage a mystery power transformer. We have plenty of choices these days, at reasonable prices.
Re: Transformer Testing
It depends on your point of view. If you do this kind of thing for a hobby and you think going through the diagnostics is fun, then you should do it. If not, you are right, there are plenty of choices. On the other hand, you can get lucky and pick up excellent iron for very low cost.
PT's are a bit easier to work out than OT's. For an OT, the turns ratio is only half the story. You can make a educated guess about ratings based on core size, but without unwinding it, you will probably never get the full story. If you get one with an appropriate turns ratio and it's "beefy" enough, it is often worth taking it for a test drive.
Of course, this is something that isn't for everyone.
Just guessing here, but Benoit probably has a 280-0-280 with some decent oomph to it. In my view, it would be worth a bit of testing to see what it's potential might be.
Benoit: I am probably wrong about that 35v winding being intended as a bias supply, as I see now it is center tapped. Still you can cover the CT with heatshrink and it will give you a nice ~50v bias supply.
Have you got any numbers on this PT on the endbell? Post them. All of them.
PT's are a bit easier to work out than OT's. For an OT, the turns ratio is only half the story. You can make a educated guess about ratings based on core size, but without unwinding it, you will probably never get the full story. If you get one with an appropriate turns ratio and it's "beefy" enough, it is often worth taking it for a test drive.
Of course, this is something that isn't for everyone.
Just guessing here, but Benoit probably has a 280-0-280 with some decent oomph to it. In my view, it would be worth a bit of testing to see what it's potential might be.
Benoit: I am probably wrong about that 35v winding being intended as a bias supply, as I see now it is center tapped. Still you can cover the CT with heatshrink and it will give you a nice ~50v bias supply.
Have you got any numbers on this PT on the endbell? Post them. All of them.
Re: Transformer Testing
I expect you'll end up with around 400 volts DC at your first filter cap with a tube rectifier. That's a lot for an EL84 amp although if you use four EL84s they'll drag the voltage down to more EL84 friendly levels. You're in the zone for a pair of 6V6s and, like I said, there's enough current available for a low voltage 6L6/5881/EL34 amp.benoit wrote:I'm in the process of testing the OT and PT from the organ amp I salvaged.
I just tested the OT in the manner described here: http://www.diyguitarist.com/GuitarAmps/ ... edLoad.htm
Putting wall AC across the primaries I read 2.5v AC on the secondaries. According to the chart it should give me 8.4k/4ohms, or 16.9k/8 ohms. Does that math sound right? If it is right, what is this useable for?
More to come on the PT.
EDIT:
Here's what I got for the PT
Red - 594 VAC, 295 to center tap
Green 35 VAC, 17.3 VAC to CT
Yellow 5.2 VAC
Orange 6.6 VAC
What can I do with this mofo? Are there more tests I should do? I guess I don't know current ratings on it and am not sure how to test them.
35 volt tap for a bias supply? It's still a little on the low side for bias. Relay supply for a Dumble clone maybe?
In all probability the current demand of the (missing) tone generator pulled the available voltage down to EL84 levels.
If you want to use octal power amp tubes it's relatively simple to run the stud for a chassis punch through the existing 3/4" socket hole, center it up by eye and punch it out. I've been re-punching 1" holes to 1 1/8" through 14 guage stainless with excellent results.
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skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: Transformer Testing
Phil:Phil_S wrote:It depends on your point of view. If you do this kind of thing for a hobby and you think going through the diagnostics is fun, then you should do it. If not, you are right, there are plenty of choices. On the other hand, you can get lucky and pick up excellent iron for very low cost.
PT's are a bit easier to work out than OT's. For an OT, the turns ratio is only half the story. You can make a educated guess about ratings based on core size, but without unwinding it, you will probably never get the full story. If you get one with an appropriate turns ratio and it's "beefy" enough, it is often worth taking it for a test drive.
Of course, this is something that isn't for everyone.
Just guessing here, but Benoit probably has a 280-0-280 with some decent oomph to it. In my view, it would be worth a bit of testing to see what it's potential might be.
Benoit: I am probably wrong about that 35v winding being intended as a bias supply, as I see now it is center tapped. Still you can cover the CT with heatshrink and it will give you a nice ~50v bias supply.
Have you got any numbers on this PT on the endbell? Post them. All of them.
I recently read in The Radiotron Handbook (third addition) that PT testing should be carried out at DC because of CEMF skewing the core saturation and heating numbers. Just a thought.
Dan H
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
-
skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: Transformer Testing
Ben:benoit wrote:I'm in the process of testing the OT and PT from the organ amp I salvaged.
I just tested the OT in the manner described here: http://www.diyguitarist.com/GuitarAmps/ ... edLoad.htm
Putting wall AC across the primaries I read 2.5v AC on the secondaries. According to the chart it should give me 8.4k/4ohms, or 16.9k/8 ohms. Does that math sound right? If it is right, what is this useable for?
More to come on the PT.
EDIT:
Here's what I got for the PT
Red - 594 VAC, 295 to center tap
Green 35 VAC, 17.3 VAC to CT
Yellow 5.2 VAC
Orange 6.6 VAC
What can I do with this mofo? Are there more tests I should do? I guess I don't know current ratings on it and am not sure how to test them.
The green wire is far more likely to be a center tap for the 6.3VAC filament winding. The voltage found there will disapear under load.
The DC resistance of the secondary windings is a fair guage of the regulation of the PT. Download Duncan's PS design software and plug in the voltage numbers with the DC resistance of the secondary then draw in a typical PS front end and then load it using PhilS parameters.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Transformer Testing
PT: F-C512-027680Phil_S wrote: Have you got any numbers on this PT on the endbell? Post them. All of them.
OT: C512-027681
Re: Transformer Testing
Sure about that?skyboltone wrote:The green wire is far more likely to be a center tap for the 6.3VAC filament winding. The voltage found there will disapear under load.
I've got red secondaries with a red/yellow CT, and the green secondaries with a green/yellow CT. Pretty sure the 35v tap is probably for the tone generators, I'd think.
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skyboltone
- Posts: 2287
- Joined: Wed May 10, 2006 7:02 pm
- Location: Sparks, NV, where nowhere looks like home.
Re: Transformer Testing
Ok, I should read closer. Never mind.benoit wrote:Sure about that?skyboltone wrote:The green wire is far more likely to be a center tap for the 6.3VAC filament winding. The voltage found there will disapear under load.
I've got red secondaries with a red/yellow CT, and the green secondaries with a green/yellow CT. Pretty sure the 35v tap is probably for the tone generators, I'd think.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Re: Transformer Testing
Sorry, this doesn't ring any bells. Didn't get lucky here. Oh well.benoit wrote:PT: F-C512-027680Phil_S wrote: Have you got any numbers on this PT on the endbell? Post them. All of them.
OT: C512-027681
Re: Transformer Testing
Yes. In my haste, I omitted this. It is appropriate to build a ss rectifier and put a cap on it. Then put a load on it. That way you test for "field" conditions. Thank you for completing the record on this.skyboltone wrote:Phil:
I recently read in The Radiotron Handbook (third addition) that PT testing should be carried out at DC because of CEMF skewing the core saturation and heating numbers. Just a thought.
Dan H
It is true that this discovery work on an unknown PT is a PITA.
I really liked Ben's idea, which is to make a virtual test with simulation software. I couldn't get Duncan's stuff to work. I think it is smarter than I am or I lack the patience.
Re: Transformer Testing
That was dan, but I agree, good thinking there. I think I will probably end up trying a 'pool or rocket, and if the trannies blow I was planning on getting some toneslut iron at some point anyway and I didn't spend a dime on these trannies.Phil_S wrote: I really liked Ben's idea, which is to make a virtual test with simulation software. I couldn't get Duncan's stuff to work. I think it is smarter than I am or I lack the patience.
Re: Transformer Testing
LOL! That was Dan addressing you as Ben!benoit wrote:That was dan, but I agree, good thinking there. I think I will probably end up trying a 'pool or rocket, and if the trannies blow I was planning on getting some toneslut iron at some point anyway and I didn't spend a dime on these trannies.Phil_S wrote: I really liked Ben's idea, which is to make a virtual test with simulation software. I couldn't get Duncan's stuff to work. I think it is smarter than I am or I lack the patience.
At that price, I would look for a reason to use that iron and see how it performs. I would probably hang a ~5K 50W load on the HT secondary to see what the drop is. For $3 you get two 2.7K 25W resistors and put them in series. That will give you a very rough idea if there are adequate mA on that winding to make it worth trying. I'm not sure I'd do it with no test at all. Do this on a fire proof surface. A 12x12 ceramic tile will do very nicely and it's non-conductive. One of those silicon mats for the kitchen is even better.
Let us know how it works out.