DC is not a good choice for heaters in displays , lights, or most vacuum tubes, because it tends to produce material migration by a process that I am not clear on, even after reading a detailed description. And probably the VF display in that combination oven would be vastly more difficult to locate a replacement for than the transformer. And now that we are aware that it is not replacing a similar transformer, there is no failed one to examine.
But now I am wondering if there is enough clearance between the winding cover and the transformer laminations to allow a single layer of #24 wire to be added to provide that voltage. That would be the graceful solution for installation with the added benefit of low cost. And even at ten turns per volt that is less than 20 turns. Certainly the task would be tedious but by no means terribly difficult. And even if there does not appear to be a gap. it should be possible to produce a gap wide enough for the thin wire. Just be careful to not scratch the insulation varnish off.

But now, knowing how the original transformer met it's end, I am wondering if any damage was done in the circuits fed by that transformer, given that doubling the input voltage will also double the output voltage in most cases.

The idea that there is more damage is bad news, but better to be aware than be surprised. Maybe there will be replacement parts if needed.
I have a transformer with an output of 2.5 volts. Is there any chance that the jump from 2 VAC up to 2.5 VAC would work? Or cause a more problems ? I will spend some time trying to locate the failure in the original winding. I will also take a look at removing windings in the 2.5 VAC transformer.

 

is there a a room on the transformer to add couple of turns on fire to make own 2V secondary?

 

For a tryout, or even a permanent installation, using a series resistor to drop the voltage from that 2.5 volt transformer is a valid choice. Less efficient but consider that (0.6 volts) x (0.2 amps)=0.12 watts. So the wasted power will not be a lot.
Guessing that the actual load is 150 mA (0.15A) and needing a voltage drop of 0.6 volts, R=V/I =0.6/0.15=4 ohms. The closest standard value is 4.7 ohms,+/- 10%, unless you can get a 4.3 ohm 5% resistor.
But before anything else, I suggest measuring the actual voltage of that 2.5 volt transformer, because that might be the voltage at the rated load current.

 

is there a a room on the transformer to add couple of turns on fire to make own 2V secondary?

Or in the case where it is varnished or hard to reveal the windings, the required number could be wound on in series, but in reverse.

 

Unfortunatly, I do not have much information about what these various output voltages do. One responder made this comment " Usually that low of an AC voltage is the heater of a vacuum-florescent display device. and an oven could certainly have a digital temperature display with a clock/timer function as well. " That is more than I know about this appliance and its controls.

As said It may have an internal fuse under the windings, can yo take any pictures of it?

 

A series resistor in the circuit is a classic way to reduce the voltage across the load. Probably it would be wise to start with a higher value than what I had calculated based on an assumed current of 200mA rating for the transformer winding. So a second 4.7 ohm resistor in series with the first would be a safe first try value.
As for the thinking that it is for a heater in a Vacuum Florescent display, that is what they were for a couple of years, prior to the liquid crystal displays becoming much better.

 

A series resistor in the circuit is a classic way to reduce the voltage across the load. .

I would say crude rather than classic, the far better way is to modify windings first, we also do not still know if it is open?

 

I would say crude rather than classic, the far better way is to modify windings first, we also do not still know if it is open?

A crude but temporary way to limit the current should not be an issue for the time it takes to verify that no other damage has been done. The resistor is for an experiment to verify that anything more will not be a wasted effort. And certainly, using a resistor to drp voltage is a classic approach, Max. Have you ever come across a line-cord resistor radio??A resistance wire third conductor in the line cord dropped the voltage to supply the heaters in the tubes. It was much cheaper than using a transformer. Also much lighter and far more compact.

 

I have a transformer with an output of 2.5 volts. Is there any chance that the jump from 2 VAC up to 2.5 VAC would work? Or cause a more problems ?

1.95V is a pretty specific voltage. If the documentation said "~2V" or even "2.0V" that would imply some wiggle room.
"1.95V" implies pretty precisely, 1.95V.

I will also take a look at removing windings in the 2.5 VAC transformer.

You will probably find it easier to add windings rather than remove them, as they are sometimes enameled and usually covered in some kind of protection, the removal of which risks damage to the windings.

You can add windings to decrease voltage, believe it or not. You just have to add them in series with the original winding with opposite polarity. Say you wrap 10 turns of wire around the core and measure the output of your new winding at 0.6V. Now you connect your new 0.6V winding in series with the existing 2.5V winding and measure 3.10V across the whole thing. That's wrong, you want it to subtract, not add, so you disconnect the connection you made previously and connect the other end of your new winding to the original winding. Now measure across the whole thing, you get 1.90V. That's just a little bit too much subtracted off, you remove half of one turn of your new wire and get 1.93V, pretty close. Try removing another half-turn and you get 1.96V. Now you can decide between 1.93V and 1.96V. I would put back on half a turn and go with 1.93V just to be safe.

 

Once again, at least for testing to see if the rest of the system is not damaged, a simple series resistor can drop the voltage a bit. NO, this is certainly not an efficient meas, but wasting a watt for a few minutes is not really a disaster. After the test is done, and hopefully the actual current draw at the 1.95 volts AC is verified, a more efficient scheme can be used.
My recollection is that the TS mentioned that the transformer is rated for six amps, vastly more than the application would require. So utilizing that transformer in any manner will be far less efficient.

 

Again, as per #15.

Per OP:
The original transformer had 4 different output voltages. 33VAC 11VAC 3.3 VAC and 1.95. I found another part number from KitchenAid that use the same plugs and provide three of the output voltages. Only the 1.95 output is missing.

From post #21 it seems that the OP found a separate TXFR for the 1.95 (2.V) ?
I would be inclined to obtain the one that requires the 2v winding and attempt to add the 8 or 10 turns probably required

 

Again, as per #15.

From post #21 it seems that the OP found a separate TXFR for the 1.95 (2.V) ?
I would be inclined to obtain the one that requires the 2v winding and attempt to add the 8 or 10 turns probably required

The transformer mentioned in post #21 was 2.5 volts at 6 amps. That is far from a tiny transformer. That is a 15 watt device, at least. Mounting it someplace may be a challenge.
Since the TS already has it in hand, I suggested using a series resistor with that transformer during a test to verify that there was no other damage to the controls. IF the rest of the system works, THEN it will make sense to add a correct number of turns over the existing windings of the replacement transformer. THAT may be possible, and even #24 magnet wire is adequate for the load of less than200 milliamps AC..
BUT there is no reason to do that until it has been verified that the rest of the system is undamaged. Whic, given the reason for the failure, might have happened.

 

33VAC 11VAC 3.3 VAC and 1.95.

Loaded or unloaded? What is the line voltage variation for your area? In my area, I treat a line voltage of 110, 115, and 120VAC interchangeably. All well designed appliances won't care.

 

I know the transformer is burnt because I wired a 240 V 4 wire plug direct on the leads from the oven. It was a used unit and I wanted to confirm it worked before I installed it. And of course, I managed to feed 240 VAC to one of the leads intended to have 120 VAC. The primary winding for this transformer if now open.

At this statement, I would assume that quite likely the Pri had an internal fuse.

 

Loaded or unloaded? What is the line voltage variation for your area? In my area, I treat a line voltage of 110, 115, and 120VAC interchangeably. All well designed appliances won't care.

110 to 120 is les than a 10% increase. 1.95 up to 2.5 is over a 25% increase. Quite a difference. In addition to that, some applications are far less forgiving than others.. And very often older equipment is more sensitive to abuse than when it was new.

 

The attempted variation by most service suppliers is to maintain a supply variation of less than 10% , on a 1.9v output, that would be hardly measurable.

 

Running up to 2.5 from 1.95 would be over a 25% step UP. For a VF display heater that is at least ten years old, I would choose not to risk it. Even if such a display was on the shelf, it would be rather expensive. AND a serious pain to replace.
So given that the try out transformer is going to be wired in with extension wires no matter what, why not use a resistor to avoid potential grief.???

It is not like I am suggesting something hard or expensive.

 

Running up to 2.5 from 1.95 would be over a 25% step UP. For a VF display heater that is at least ten years old, I would choose not to risk it. Even if such a display was on the shelf, it would be rather expensive. AND a serious pain to replace.
So given that the try out transformer is going to be wired in with extension wires no matter what, why not use a resistor to avoid potential grief.???

It is not like I am suggesting something hard or expensive.

Because the resistor solution requires the load to draw at least a certain amount of current or else the display will be subjected to overvoltage.

 

Because the resistor solution requires the load to draw at least a certain amount of current or else the display will be subjected to overvoltage.

Certainly that is true. And thus I did suggest values for the resistor. What makes the most sense is to measure the load first, and then decide the resistor. With a heater the resistance will rise a bit as it heats, and so measuring the load voltage after a warmup will be a good move. No, the number will not be exact but it should be close enough for tryouts. IF the TS owns a suitable variable resistor that may be even better.. Some folks do own stuff.
Probably a 100 or 200 ohm wirewound variable will be suitable for the application.
Given that the transformer rating for that winding was 200 mA, if the load were also 200, then the resistor would be 4 ohms.If it is 100, then 8 ohms, so the fixed resistor would be 8.2 ohms as a standard value.

 

IF the TS owns a suitable variable resistor that may be even better.. Some folks do own stuff.

Indeed. I own so much stuff that I my attempts to use stuff are hindered by my inability to find to stuff among the overabundance of stuff. It's a vicious cycle.

I agree, if the TS has a potentiometer, putting it in series with the transformer output would be a quick & easy way to rule out the VFD being already toasted.