fender Blues DeLuxe Reissue ate two PT,s fuse not blown and correct value

[fester gomez]

hello , I have a fender blues deluxe reissue (looks brand spanking new, I can tell it was never gigged) that has eaten 2 PT's, only the primary side. It was given to me to repair and there doesn't seem to be anything out of the ordinary. The main fuse did not blow either time it went down, and it is the correct value. Any info or direction would be greatly appreciated. thank ya fes

[Mark Black]

Just to be sure we are talking Power Transformer right?

I wonder has the amp had a history of being left on for long periods in a warm environment? Reason I ask is with an open primary my first suspicion is of a thermal fuse which is almost certainly embedded in the transformer windings (and generally considered to be unrepairable or at least not cost-effective). Actually any condition that causes the transformer to run extra hot might take out that fuse over time, and though others disagree with me I also suspect power transients too fast to blow the line fuse could be a culprit.

[g1]

Thanks for the correction Mark, for some reason I mis-read as output transformer, so I've just deleted that previous post.

[teemuk]

Usually when a thermal fuse integrated to a transformer fails it indicates that the transformer has been subjected to temperatures where winding insulations and other similar components may have taken enough damage to become unreliable.

So it's not just about cost-effectiveness of replacing a thermal fuse, it's about the transformer being potentially hazardous component needing entire rebuilding once it has been cooking at temperatures at which the fuse failed. If it was just about tripped fuse it wouldn't be rocket science to make the fuse resetable, like many discrete thermal fuses are.

So, at the point the fuse goes the practical solution is indeed getting a whole new transformer.

[Mark Black]

Did a little reading over the last few days and found most of the thermal cutoff manufacturers warn against subjecting the device to high vibration. Or operating at temperatures below (but near) the cutoff opening temp.

Like maybe in a guitar combo amp?

But we are saved! Go figure...

[Audiotexan]

hello , I have a fender blues deluxe reissue that has eaten 2 PT's, only the primary side.

Just so we have a bit more history/perspective to go on:

It's eaten two PT's...over time (months/years)? Or back to back (meaning: replaced the bad one, and it immediately killed the new one)?

Used in an area with poor power regulation/recent storms?
(Thinking mains spikes taking out the primaries)

Used in an ungrounded house?
(50's wiring)

[gui_tarzan]

If the house wiring is bad (no ground, voltage on neutral to ground, inadequate supply) I can see how it would damage the PT primary very easily. Our house is over 100 years old and the wiring has been "updated" several times. More like added to actually, and it still has the 1950s breaker panel which I'm going to be updating. At one point I had voltage from neutral to ground so I separated a couple of circuits and have clean power now. This is the second time in seven years I've had to have the power company come out and make repairs on their end and at our previous house they had to repair their equipment too because it was causing us issues. Just a couple of weeks ago we were experiencing brown-outs where our voltage was dropping from 120+ to around 50v, which can roast electronic devices very easily. I had the power company come out and they fixed the connections up on the pole and we haven't had any issues since.

I would have your buddy get his house checked asap, there may be issues there causing his amp problems. Worst case it can cause a fire, best case maybe one circuit is faulty. If your state is anything like Michigan, the consumer protection agency that monitors utility companies can be a great help if the utility provider isn't. If it's inside the house, that's another whole issue but it needs to be checked.

[Chuck H]

It looks like Fender has some trouble with this sort of thing in their mid size combo's.

http://music-electronics-forum.com/t36213/

http://music-electronics-forum.com/t31325/

Am I starting to see a pattern?

[J M Fahey]

Well, a respected Tech I know often has 15 to 30 (no, not a typo) Egnater amps with cooked PTs.
And Factory only answer has been to send more of the same, but with crudely hand drilled holes in the PT covers (no kidding) "for ventilation" plus a PC type 12V fan and a rectifier kit to run them from filament voltage.
No kidding

So *maybe* Fender got the same PT supplier.
Or an equivalent one.

[Alan0354]

Anyone actually open the bad PT to find out what exactly gone wrong? Sounds speculation about fuse. I would like to see where it breaks if I have two burn in a roll.

[Enzo]

It looks like Fender has some trouble with this sort of thing in their mid size combo's.

From just three threads?

Bad transformers happen, but when a particular amp eats multiple transformers, I tend to think it is the amp. Just my opinion. Seems to me if ten transformers are going to fail it is more likely they will be in ten amps rather than three.

[Alan0354]

I would open the transformer to find where it open before I make any conclusion. It just does not make sense to me that they build in an internal weak spot so it open up if it is too hot and trash the transformer. Can it because of a bad solder?

[J M Fahey]

It just does not make sense to me that they build in an internal weak spot so it open up if it is too hot and trash the transformer

Thatīs the logic behind the foil wrapped fuses: why make something designed to fail under overload?

[Alan0354]

Thatīs the logic behind the foil wrapped fuses: why make something designed to fail under overload?

I don't agree with putting in fuse thing. To me, it's just ways to get money from the user. They should use the main fuse as the one to blow.

I would still open the transformer instead of chucking it to the fuse inside.

I have only the old Fenders, The PT never even get that hot that I cannot touch. To me, the warmth is more because they are right behind the power tubes. Maybe the new Fenders don't design with as much margin. The few old Fenders never give me problem except the filter cap blew one time. They last forever.

[Audiotexan]

It looks like Fender has some trouble with this sort of thing in their mid size combo's.

http://music-electronics-forum.com/t36213/

http://music-electronics-forum.com/t31325/

Am I starting to see a pattern?

Hrrm...nah. Bad batches *never* happen! lol :X
<moves out of the way before lightning strikes>

But seriously... Good call on pulling old links. Neither of the two above yielded a 'fix' per se, however, in following through the first link g-one provided yet a third link (post #6) which had gone through 2 trannies as well, and DID include the author getting back with a fix for his! http://music-electronics-forum.com/t23057/ which in post #32 said:

My amp is repaired now. I had replaced the power supply transformer and slowly took the power up using a variac. We checked the caps and diodes, all seemed Ok in circuit. Once the input voltage was increased to near 110 volts, we saw the current on the variac start to rise - the plates of the 6L6's started to glow. What had happened was the bias pot was on a dead spot - a quick spray with some cleaner and adjustment of the bias pot and the bias voltage was back to normal and voila! A simple fix this time around.

Wonder if the bad batch wasn't transformers... but bad pots?!
(A much cheaper fix, but causing expensive problems.) Given the "rash" of examples, and how cheap the prevention would be, I have to wonder if it wouldn't be a good idea to toss a new bias pot into any HRD that comes in (that hasn't cooked it's PT *yet*). /speculation off

Guess time will tell...