Cooked OT

[jestaudio]

pretty sure i cooked my OT, syntoms were clound of white smoke, very low distorted output and on check over one tube on the output running red hot and one barely warm, voltages look ok, within 0.2 on either tube
havent got a spare for it but i suspect that i may have had a bit to much on the centre tap,

The readings i have across the primary side is 72.1-73 with 140 between the windings, a bit low to say the least

[UR12]

pretty sure i cooked my OT, syntoms were clound of white smoke, very low distorted output and on check over one tube on the output running red hot and one barely warm, voltages look ok, within 0.2 on either tube
havent got a spare for it but i suspect that i may have had a bit to much on the centre tap,

The readings i have across the primary side is 72.1-73 with 140 between the windings, a bit low to say the least

Swap your tubes around and see if the same one gets red in either socket. Of course power it off as soon as you see it starting to go red. If the same tube goes red in either socket then it's the tube and not you OT. If the other tube goes red on the same side as the original then it may be your OT but from your static reading (If you mean ohms) that could be a normal reading.

[jestaudio]

pretty sure i cooked my OT, syntoms were clound of white smoke, very low distorted output and on check over one tube on the output running red hot and one barely warm, voltages look ok, within 0.2 on either tube
havent got a spare for it but i suspect that i may have had a bit to much on the centre tap,

The readings i have across the primary side is 72.1-73 with 140 between the windings, a bit low to say the least

Swap your tubes around and see if the same one gets red in either socket. Of course power it off as soon as you see it starting to go red. If the same tube goes red in either socket then it's the tube and not you OT. If the other tube goes red on the same side as the original then it may be your OT but from your static reading (If you mean ohms) that could be a normal reading.

tried 3 sets of good tubes with the same result

[Phil_S]

Your OT has DCR readings that seem a bit too symmetrical and therefore problemmatic. To achieve the same number of turns, the outer half of the winding has to go a further distance. IMO, you should see more of a differential since the outer wire is maybe 10-20% longer. Even so, it may be that this particular PT ohms correctly. There may be an internal short that isn't a full contact short detected when metering for DCR, but when you apply power, those pesky electrons are quite determined to find the shortest path. White smoke is a bad sign. If you don't see anything else burnt, your OT is likely toast.

You can disconnect it, run 6.3v or 5v filament supply into the secondary to see what it delivers on the primary. This tells you the turns ratio, which is the square root of the impedance ratio. If it isn't what you expect, then you can be pretty well assured it is now a paperweight or a door stop, depending on it's size and your personal taste.

[jestaudio]

Your OT has DCR readings that seem a bit too symmetrical and therefore problemmatic. To achieve the same number of turns, the outer half of the winding has to go a further distance. IMO, you should see more of a differential since the outer wire is maybe 10-20% longer. Even so, it may be that this particular PT ohms correctly. There may be an internal short that isn't a full contact short detected when metering for DCR, but when you apply power, those pesky electrons are quite determined to find the shortest path. White smoke is a bad sign. If you don't see anything else burnt, your OT is likely toast.

You can disconnect it, run 6.3v or 5v filament supply into the secondary to see what it delivers on the primary. This tells you the turns ratio, which is the square root of the impedance ratio. If it isn't what you expect, then you can be pretty well assured it is now a paperweight or a door stop, depending on it's size and your personal taste.

Its probaly my own fault for assuming to much, its only a cheap chinese OT that came with chassis, it was running 6l6,s so i asummed it would handle pushing the plates at 380, eveidently not

[Structo]

Boy, once you smell a fried transformer, you will never forget that smell.
Good to file away in the brain until you smell it again, then you'll know!

I have had a bad 6L6 redplate before out of the blue.

Luckily I had the amp turned where I could see the tubes.

Problem followed the tube.

Funny thing is it was TAD 6L6 STR, the same tubes I like in my 100w ODS.

[Jana]

Phil, If a transformer has interleaves, then the DCR for each half will be very close. Regardless, it does sound like this OT is a paperweight.

[Phil_S]

Phil, If a transformer has interleaves, then the DCR for each half will be very close.

Hmmm...I admint I hadn't thought about that. Thanks for (re)educating us.

Regardless, it does sound like this OT is a paperweight.

Yeah, especially considering the OP's most recent comment.

[C Moore]

Phil, If a transformer has interleaves, then the DCR for each half will be very close. Regardless, it does sound like this OT is a paperweight.

Can you explain that for a beginner please.?
Thank You

[Jana]

Okay, I'll try. When the window is open and a breeze is blowing in, the papers sometimes fly all over the place--so, the paperweight is a handy item to put on the papers.

Oh, the interleave thing. The number of interleaves varies but the most common for guitar amps (non-hi fi) is to wind half of side A, wind side B, and then finish off with the rest of side A. Both side A and side B have the same number of windings, and also have very close to the same length of wire. Hence, the DCR is the same for both sides.

I have a 50W plexi transformer sitting here waiting to be used that measures within 1/2 ohm DCR difference between the 2 sides. It is interleaved like I just described.

[C Moore]

OK.... so a "non-interleave" would wind all of one side and then all of the other side on top of that. While having the same "number" of windings, the outside winding would have more length of magnet wire, and therefore more resistance.
Is that kind of what happens.?
Thank You
btw....goood one with the paper weight...

[Cliff Schecht]

You got it right.

Interleaving in transformers is something that isn't discussed often enough. The winding pattern used in the interleaving will have an affect on the overall sound of an amp. The pattern of interleaving chosen (ignoring different wire gauges and core materials) will have parasitics that determine the bandwidth and Q of the output transformer. Also some patterns aren't so good about getting the winding resistance right on which introduces some imbalance in the OT. This adds some asymmetry when the power stage distorts (this is more noticeable with a lack of negative feedback to the PI).

[M Fowler]

And what should I do with a bad OT from Heyboer send it back to be checked out or paper weight? I don't need anymore paper weights.

[Phil_S]

And what should I do with a bad OT from Heyboer send it back to be checked out or paper weight? I don't need anymore paper weights.

If it's been bad, you should punish it. Maybe that will curb it's being bad.

One option is to take the opportunity to take it apart. I think everyone who does what we do needs to take a transformer apart. It will give you new respect for what we often think of as a hunk of iron.

If you get lucky, you may find the problem is near the outside, in which case you may be able to rewind/repair it yourself.

If you think the Heyboer folks are responsible for a defect, then, by all means send it back. Otherwise, I doubt they will be interested.

People will sell blown iron on eBay for people who do their own winding. Yes, they are out there. It will probably fetch around $10.

[C Moore]

I have seen the term interleaving.....always wondered what it meant, and why it was done. Was it something that was more common in the past than it is now.?
Just finished rebuilding a friends SF Bassman. It had a weird problem with notes distorting as the "decayed". Considering I rebuilt the entire amp, I just figured I had done something wrong. It took me a month to try a different OT. Turns out the Heyboer was bad. It came with the amp.....the receipt said it was just under one year old. But who knows what the original owner did to it. Maybe they dropped it, put it in a microwave, ran it into a 150 Ohm Impedance for a long time.....who knows.?
Phil said that Heyboer would certainly replace it if it turned out to be their fault. But I would have to pay to ship it back, and if it was not their fault.......
So now it justs sits with my friend. It was tapped for 2 and 8 Ohms. I never tried it on the 2 Ohm tap. It may be good with 2, or it might be bad all the way to the front end, and not even be a good choke/coil. I will never know. Transformers continue to amaze me.
Best