Two seperate "push" & "pull" windings instead of one winding with a CT?

[jeff]

  Guys, I really need help here. I'm scratching my head trying to figure this one out.
Would anyone make an OT with a seperate winding for the "push & "pull" sides of a primary instead of one winding with a CT? In other words instead of one 8K coil with a center tap, two 4K coils that you have to physically connect each winding to the power supply?

This OT has a red,blue,black and a red/yellow,blue/yellow,black/yellow. on both there's ~23 ohms between the red & blue, ~90 between blue & black and ~120 between red & black.
 Is this to wire different primary loads? (ohms in parantesis)

]||[----Black\            
]||[      (99)  \
]||[----Blue   (122)
]||[      (23)   /
]||[----Red--/
]||
]||
]||[----Red/Y-\
]||[      (23)     \
]||[----Blue/Y  (112)
]||[       (89)    /
]||[----Black/Y/

Maybe you get different primaries by:
   connecting the reds and using the blacks to plates
   connceting the reds and using blues to plates
or connecting the blues and using blacks to plates
   ???

Or maybe it's an ultra linear where blacks go to plates blue to screen reds have to be connected to power supply?

Anyone have an idea?
Why no CT?
Maybe this isn't an OT?

[Willabe]

Maybe this isn't an OT?

Where did you get it from?

What's on the other side?



              Brad     

[kagliostro]

An OT with Ultra Linear intakes and windings to be joined as to have the CT ?

K

[jeff]

"Where did you get it from?
What's on the other side?"

                  ]||[----Black\           
                  ]||[      (99)  \
                  ]||[----Blue   (122)
black--------]||[      (23)   /
                  ]||[----Red--/
green--------]||
                  ]||
yellow-------]||[----Red/Y-\
                  ]||[      (23)     \
light yellow--]||[----Blue/Y  (112)
(faded         ]||[       (89)    /
orange???)   ]||[----Black/Y/


It's an old transformer my brother sent me. I actually thought it was a PT because the color is kinda fading and the black, green, yellow, lighter yellow on the secondary looked at first glance to be two greens and two yellows so I thought 6.3V and 5V but that's not what it is because there's continuity between all four. I thought blue, black, blue/Y, and black/Y were 120V inputs to be wired either series or parallel for 240V or 120V operation(which I have seen before) and the red & red/Y was the B+. Glad I took a closer look before I used it as a PT!

"An OT with Ultra Linear intakes and windings to be joined as to have the CT ?"

That's the only thing I can think of but I've never heard of such a thing.
I put a voltage on the primary to measure the secondary but I don't think my meter is super accurate. Depending on what input voltage I use it seems to be ~ 4K-5K:2,4,8 from black to black with reds connected(small errors add up to big ones when you're squaring things)

Anyone ever heard of this "split winding" setup?
How could I test if the taps are ultra linear taps or used for somewthing else? I know how to test a regular OT for impedacne but what do I look for to tell if the taps are UL taps? I don't know for sure if it's supposed to go red to red with black to plate and blue to screens or black to black with red to plates and blue to screens.
I guess if I put a voltage for red to black I'd know which is plate and which is CT because the blue would be 40% of the input voltage one way and 60% the other?

[sluckey]

Have you ever measured the dc resistance of an 8Ω secondary winding?

[jeff]

In general or this one's?
I get .8, but I get .3 touching the two leads of the meter together.

Why do you ask?

[jeff]

OK If I put 5V from red to black, I measure 1V from red to blue and 4V from blue to black.
Not the 40%/60% I was expecting more like 20%/80%
Is this any clue if the blues are UL taps?

[sluckey]

I asked because I did not see any resistance readings that would indicate a near zero ohm secondary winding. After reading your posts again I see you mention "continuity between all four", but that's kinda vague. Continuity can mean any resistance reading, 1Ω, 100Ω, 1000Ω, 1MΩ, etc. Now I see you do have a low reading, so disregard.

[jeff]

Sorry 'bout that I just heard the meter beep and didn't bother to check 'cuz at first, when I didn't notice the slight color difference, and I assumed they were 6.3V and 5V windings and I thought they were shorted.

Never realized how low speaker taps were til you brought that up

Thanks
  Jeff

[DummyLoad]

"Where did you get it from?
What's on the other side?"

                  ]||[----Black\           
                  ]||[      (99)  \
                  ]||[----Blue   (122)   
black--------]||[      (23)   /           
                  ]||[----Red--/           
green--------]||
                  ]||
yellow-------]||[----Red/Y-\
                  ]||[      (23)     \
light yellow--]||[----Blue/Y  (112)
(faded         ]||[       (89)    /
orange???)   ]||[----Black/Y/

use caution!

1) tie off all the leads to some barrier strip(s).
2) connect the red and red/yellow together.
3) with a lamp limiter, apply 120V/240V (or whatever the line V is where you live) to the black and black/yel.
4) measure and record VRMS from black to black/yellow (yes, the line voltage ;) )
5) measure and record VRMS from black to green, then black to yellow, then black to orange.

post results. or, calculate turns ratios yourself (Vpri)sq / (Vsec)sq = TR. now multiply TR by the load resistance you would apply to secondary and that will be the primary impedance.

ex. i have a sears silvertone 1484 OT i need test:
i apply 120VRMS to the primary (plate to plate) blue to brown leads and i measured the following:
1) black to red/yel = 3VRMS
2) black to yel = 3.62VRMS
calculate:
1) for primary (VpriSq) = 120*120=14400
2) for secondary black to red-yellow (VsecSq) = 3*3=9
3) divide pri/sec = 14400/9=1600
4) now pick a load - i want 4 ohms on the blk/red sec taps so then 1600 * 4 = 6.4K:4 that confirms that this is likely a 6.6K:4ohm transformer ratio.

how about the 2nd secondary (black to yellow)? ok, 3.62*3.62=13.1 then 14400/13.1=1099. now we know it's a probably a 6.6K part but lets say we apply 6 ohm to this tap, so then we have 6.5K:6 transformer ratio, or with an 8 ohm load you could make it 8.8K:8.

on a footnote, it IS a small OT for a pair of 6L6GC even if they are running in cathode bias. maybe that's why we see so many 1484 silvertones with a replaced OT.

--pete

[jeff]

OK
 
Anyone come up with a reason for two seperate coils and not one CT. Seems like if the Xformer manufacturer could save money with only one wire they would.

Is there any application that would call for seperate coils?

[HotBluePlates]

Is there any application that would call for seperate coils?

No, not exactly at least for push-pull.

The coils have to be on the same core, and wound in a particular way. And the shared ends that would be a CT have to be connected to the B+.

But that said, there are many ways to sectionalize a winding, to reduce certain parasitic elements of a transformer and improve bandwidth. In such a winding setup, it may be easier for the manufacturer to bring out the ends of the windings to leads or terminals on the case. UTC did this a lot with their transformers, and Lundhal and Sowter do it now (and there are probably others).

Sorry 'bout that I just heard the meter beep ... I thought they were shorted.

Keep in mind most meters don't indicate continuity only for 0Ω, but often for other lowish values. Could be 20Ω, could be 100Ω depending on the meter.

And an OT secondary (or heater winding) has to be a coil of pretty thick wire for low voltage, high current and so tends to be low resistance.

[jeff]

Any advice on the UL taps?
Pros and cons?
Does the fact that I applied 5V to red and black and measured 1V from red to blue and 4V from blue to black suggest that red is theCTts and black are the plates or that the blacks are the CT and reds are the plates with recpect to using the ULs.

In other words I could use reds as CT and blacks as plates or the blacks as CT ands the reds as plates if I didn't use the UL taps, but if I do use the UL taps my screen voltage would be different in each case.

Can you tell by reading ohms? Should the UL taps have more resistence between the CT than the plates or more resestince between plates than the CT?

Which makes more sence for the ULs?
     ]||[----Black\-----plate            
     ]||[      (99)  \
 UL-]||[----Blue   (122)
     ]||[      (23)   /
     ]||[----Red--/---|
     ]||                   CT
     ]||                    |  
     ]||[----Red/Y-\--|
     ]||[      (23)     \
UL-]||[----Blue/Y  (112)
    ]||[       (89)    /
    ]||[----Black/Y/-----plate

OR

     ]||[----Red/Y-\-----plate
     ]||[      (23)     \
UL-]||[----Blue/Y  (112)
     ]||[       (89)    /
     ]||[----Black/Y/---|
     ]||                     CT
     ]||                       |
     ]||[----Black\ -----|          
     ]||[      (99)  \
UL-]||[----Blue   (122)
     ]||[      (23)   /
     ]||[----Red--/-----plate

[PRR]

The reds obviously go together to B+.

The Blacks are Plate leads.

The UL ratio is so very low that you may as well tape-off the Blue leads.

Why separate the Reds? Yes, a common Red would save a lead, but a splice inside the transformer (especially across two windings) can be problematic. Also there are odd totem-pole output topologies that need separated windings. Or an industrial/broadcast application may call for current-sense points for each tube. Or maybe just designer's preference.

[jeff]

OK I did some measurements per Dummyload's instructions.
 
Looks like 5K:2,4,& 8

Is it possible that blacks are CT and reds give 5K:2,4,& 8 and blues give 3.2K:2,4, & 8?
Haven't measured, but on paper I think that's what you'd get.

Thanks for all the help guys
   Jeff

[HotBluePlates]

Anything is possible.

If the transformer is very old, it probably doesn't have multiple load impedances like you're thinking. I'd guess they are 20% UL taps.

[DummyLoad]

Is there any application that would call for seperate coils?

No, not really. Maybe just the winder's preference.

[HotBluePlates]

Here's a 1956 article that helps explain why the transformer manufacturer would sectionalize the windings.

Like I said, often, this is done and you're none the wiser because the relevant sections are connected internally and brought out via wire leads.