Damage using ext speaker jack

[bluesguitar]

After doing some work in the chassis I tested my amp with my speaker accidentally plugged into the external speaker jack. I had to turn the volume up higher than usual, and the signal was overdriven. After realizing the error I plugged it into the correct speaker jack. All seemed okay. I have plenty of volume. How would you know if you had done damage to the OT? What are the symptoms of a damaged OT?

[martin manning]

If it sounds good, then there is probably no harm done. You don't say what amp, and the potential for damage depends on how the speaker jacks are wired. I guess since you had sound when plugged into the extension jack we can assume that it is not wired with a switched/shorted main and a non shorted extension (Fender/Marshal-style). Since you say you had to turn up more than usual and the sound was distorted, I'm guessing there is some kind if impedance switching function involved.

[Phil_S]

You had a load on the OT, it was only a short time, and you have good volume from the correct jack. Probably nothing happened.

If you really want to know, there are two things you can do. One is to disconnect the OT, apply low AC voltage (from a 5V or 6.3V winding works well) to the secondary, read the voltage that comes out on the primary, and calculate the turns ratio to see if it is about what's expected.

The impedance ratio is the square of the turns ratio. So, if it is 8K to 8 ohms, the impedance ratio is 1000:1 and the turns ratio should be sqrt(1000) = ~31.62. If you input 5V to the 8 ohm secondary, expect 31.62*5 = 158VAC at the primary.

Beyond that you can do the neon bulb test for shorts. http://www.premierguitar.com/articles/14403

[bluesguitar]

If it sounds good, then there is probably no harm done. You don't say what amp, and the potential for damage depends on how the speaker jacks are wired. I guess since you had sound when plugged into the extension jack we can assume that it is not wired with a switched/shorted main and a non shorted extension (Fender/Marshal-style). Since you say you had to turn up more than usual and the sound was distorted, I'm guessing there is some kind if impedance switching function involved.

Actually it is a fender (Super Reverb). I looked on the schematic (AB763) and it looks like the main speaker jack should short without a cable inserted. How I got sound thru the external jack I'm not knowledgeable enough to know. I only played it for a minute or two and later was relying on that safety short for insurance. I just know that the impedance would have been different in the external jack and maybe overload the OT. All appears to be okay with the amp. Still working out some bugs and wanted to know what sounds may be attributable to the OT, and what I can rule out. Thanks

[Reeltarded]

i have a BF twin cut into a head where i do this on purpose for durations longer than most gigs.

ehh we'll see..

[martin manning]

So the switching function on the main jack is just not making good contact. Since you had a load connected I doubt there has been any damage. Cleaning that contact would be a good idea, and maybe adjust it's tension if necessary. Dragging a strip of paper soaked with contact cleaner through it is a good method for cleaning- don't use abrasive since you don't want to cut through the plating.

[Structo]

Yes it is probably alright.

If you didn't smell anything funny....

I had a bad speaker cable (open) on my D'lite 44 amp and I couldn't figure why I wasn't getting any output.
I didn't run it very long each time I tried it and I don't think it hurt it after I got a new cable.

[BTF]

If it's any comfort, years ago I did the same thing to a Showman head. Speaker plugged into the wrong jack. I played it for several minutes that way until I figured that a mate had plugged the speaker in incorrectly. That Showman is STILL playing with the same trannie.

Good Luck!

[Structo]

So at this point what I suggest you do is install a new shorting jack for the main speaker and label the rear control panel so it is clear what jack is what.

Here is the jack you need.
http://www.tubesandmore.com/products/W-SC-12A

Usually it is Spkr and Ext Spkr.
So in other words you should have the the speaker you use all the time in the Spkr jack and additionally if needed, a extension speaker into the Ext Spkr, being midful of impedances.

Just my $0.02

[bluesguitar]

I'm not certain all is okay with the OT. Although the volume of the amp appears unchanged it definitely lacks sparkle and dynamic richness. There seems to be more gain, and at first I thought it sounded warmer. However, the longer I played the more monotonous and one dimensional the tone seemed. I've been working in the chassis to try and debug some idle rustling/static. I changed a few resistors that were out of spec, and the rustling/static was diminished. But now I have tone that is also diminished. Other than a short test for volume, I hadn't had a chance to test the amp since accidentally plugging the speaker into the wrong (ext spkr) jack, so I have no reference for any sonic change from that accident alone. The voltage on the center tap of the OT is 456, which is down 10 volts from the last check. The schematic calls for 465. How important is the OT for the sparkling clarity and richness of your tone? Other than advertisements pushing their products there seems to be a lack of info on OTs and their sonic contribution. Especially the sonic symptoms of a sick OT, compared to a healthy one.

[Reeltarded]

There is no such thing as bulletproof, but the closest thing I know to it is a Fender OT.

Your resistors drifted in value over time. When you replaced them you went to the spec values. Over the course of changing a couple the tone changes. they usually drift up by around 15-20%. 820R becomes 1-1.1k or so... like that. It is pretty normal to meter the old components and match those values to sound closest.

There are different levels of sick in an OT from what sounds like the static on a television to muffled blatting with massive inputs only. All the world is a flyback lightning storm. heh

I am betting your OT is just fine. I seriously have more hours on this BF Twin head in ext than the normal output jack. Hours at a time with the output around 3 and lots of gain on the front. It isn't good for it but that is the deal. Sounds insane!

[Leo_Gnardo]

I'm not certain all is okay with the OT.

More likely you wore some of the sparkle off your output tubes. Transformers in distress do much worse than sound "tired." Worn-out output tubes do get to a tired-out stage, and the sound gets flabby especially in the bass. Perfectly good if you like a worn-out tone. New ones tend to sound sharp & bright.

[bluesguitar]

I am betting your OT is just fine. I seriously have more hours on this BF Twin head in ext than the normal output jack. Hours at a time with the output around 3 and lots of gain on the front. It isn't good for it but that is the deal. Sounds insane!

I would think your Twin also has a safety short on the main spkr jack. I'm just curious as to how signal gets to the speaker thru the external jack. Seems like the short wouldn't be doing it's job.