OPT defective ?

[Colas LeGrippa]

Hola amigos,


What would cause an OPT  to  pass DC voltage to the point to blow a speaker ?


Colas

[Latole]

Never see or ear about that.

What would have caused this; bias too hot of the power tubes for the capacity of the transformer in my opinion

What amp is this?


With what you say in theory there would be a direct short circuit between the primary and the secondary.
Which seems quite surprising to me and perhaps impossible

How many volts do you measure at the speaker ?
The windings of a transformer are easily measured with an audio generator. we have already discussed the procedure in the forum

[acheld]

I've never seen that either, but there needs to be a short between the secondary and the primary IF the DC voltage is not getting into the speaker jack from somewhere else.   Should be easy enough to test.   

For example, I always provide an impedance switcher for the speaker jack, and that implies extra wiring (a little messy) near some of tubes.   That seems an unlikely source for a short, but it's good to keep an open mind about where a short has occurred.   Crazy stuff does happen.

[PRR]

Most tube amp power supplies don't make enough current to blow a speaker.

500mA, 0.5A, is a lot for a tube power supply. Thrown into an 8 Ohm load, that is 4 Volts and 2 Watts. No guitar-duty speaker should die at 2 Watts.

Why do you think it was blown by DC passing though the OT? Why not the good old "got drunk, played too loud" excuse?

[AlNewman]

Is it possible a coupling cap went between the NFB supply?

[Colas LeGrippa]

I was trying to fix my SE build with a speaker connected when I heard a pop from the speaker and then, nothing. Coil speaker measured open.
I havent had time to work on it further more.


I have to measure all the voltages and bias.


So , too much power into a too weak speaker burned the coil. I ll check the OPT to make sure its good b4 plugging other speaker

[Latole]

 "I heard a pop from the speaker and then, nothing. "
-Colas LeGrippa

I read that the voltage across the transformer is only a hypothesis
se. Nothing was measured. Only a loud "pop" was heard destroying the HP coil.

Your last answer seems to show that simply too much power was sent to the speaker.

With a voltmeter and a resistor, instead of a speaker, you could read the voltage present at the transformer secondary.
The "pop" may also have been only temporary such as turning the amp "on" ?

[Platefire]

I had something similar happen in the 70's. I had a Silverface Bandmaster and the head went down and had to get it worked on. The band had a gig to do, so I borrowed a Peavey Musician head from a friend and ran it through my Bandmaster 2-12 cab. On the last song for the night both speakers blew at the same time. I always wondered how that happened? I was trying to hold the volume down. Well I got the speakers re-coned, got my Bandmaster head back and moved on. What I get for playing through a SS with probably a 100++ watts

[Latole]

I had something similar happen in the 70's. I had a Silverface Bandmaster and the head went down and had to get it worked on. The band had a gig to do, so I borrowed a Peavey Musician head from a friend and ran it through my Bandmaster 2-12 cab. On the last song for the night both speakers blew at the same time. I always wondered how that happened? I was trying to hold the volume down. Well I got the speakers re-coned, got my Bandmaster head back and moved on. What I get for playing through a SS with probably a 100++ watts

Peavey Musician is a 210 watts amp.
Bandmaster is 40 watts amp , cab speakers  ?  100 watts or less ?

[Platefire]

Well the thing about it is I somehow thought all the years it had shorted HV into the speaker wires and destroyed the speakers, just like Colas. I can see now that I know something about Guitar amps, that it's highly unlikely it happened that way