# DC on speaker -YBA 1



## ed2000 (Feb 16, 2007)

1966 Traynor YBA 1, serial in the mid 300's
When I hit muffled strings hard the speaker cone oscillates slowly several cycles even though sound is stopped. I suspect low voltage DC + and - is leaking (I would guess less than 5 V based on cone movement compared to when attaching a 1.5 V battery).
I suspect the PS caps are original (none replaced within 30 years). There is minimal hum. I'd like to solve the issue without using the shotgun approach in replacing every cap. Or should I do a complete cap job and hope to cure it? The head is used intermittently because my Vox Pathfinder 15r does it all for me..


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## loudtubeamps (Feb 2, 2012)

If the electrolytics are original then I would replace all. If the low freq. oscillation still persists, then you can start troubleshooting.
I would suggest that doing a _partial_ cap replacement is like changing _some_ of the spark plugs in an engine when it is running rough.
Change all of them and eliminate the obvious things first. 
cheers, doug


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## nonreverb (Sep 19, 2006)

"1966 Traynor YBA 1, serial in the mid 300's
When I hit muffled strings hard the speaker cone oscillates slowly several cycles even though sound is stopped. I suspect low voltage DC + and - is leaking (I would guess less than 5 V based on cone movement compared to when attaching a 1.5 V battery).
I suspect the PS caps are original (none replaced within 30 years). There is minimal hum. I'd like to solve the issue without using the shotgun approach in replacing every cap. Or should I do a complete cap job and hope to cure it? The head is used intermittently because my Vox Pathfinder 15r does it all for me.."



Here's my take on the situation:
1. There could not be DC on the speaker as it would have literally caught fire if any B+ DC jumped windings on the output transformer...450 or so volts will destroy a speaker instantly.
2. Slow oscillation could not be bad caps. Even if the caps were bad you wouldn't be able to detect the cone movement as it's too fast for the eye to see plus if there was sufficient ripple to move the cone, the hum would be REALLY loud.
Are you shure that when you hit the strings that they aren't still vibrating for a short duration? It almost sounds as if the harmonics are passing through.


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## jb welder (Sep 14, 2010)

nonreverb said:


> Are you shure that when you hit the strings that they aren't still vibrating for a short duration? It almost sounds as if the harmonics are passing through.


 Agree with this, not sure there is a real problem here. If you couldn't see the speaker, is there a problem sound wise? Cone movement that you can see is probably lower than any frequency you can hear. DC moves the cone in or out and it stays there.
It seems the movement you are seeing stops after a few cycles? Maybe the cone is just less stiff or the amp has less damping than whatever you are comparing it to?
I would think just having your palm muting the strings, any slight movement of your hand would produce some cone movement.


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## washburned (Oct 13, 2006)

I'm betting subsonic frequencies from muted strings, if movement only occurs when string is plucked.


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## ed2000 (Feb 16, 2007)

I'll try to put a short vid on youtube..a pic's worth a thousand words. This oscillation happens with different speakers.


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## jb welder (Sep 14, 2010)

Not meaning to sound rude, but what you see is not relevant. Sound problems are relevant. So please describe the problem you are hearing. If there is no sound problem, and the speaker was behind grille cloth, would you have noticed anything?
If there were some weird DC or low freq. problem "even though sound is stopped", then it should also occur when your guitar volume is turned off, or when the amp has nothing plugged in to it.


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## loudtubeamps (Feb 2, 2012)

We know that it's not D.C. but assume by your description that it is a low frequency oscillation or after ring.
If it was persistant I suppose one would assume motorboating would be the diagnosis.
I can only suggest again that until you freshen up the amp you may or may not find the problem.
Does it have new or different tubes? Have their been any mods recently? Is this a recent purchase?
_We_ need any and all info to help solve the puzzle for you. Fun ain't it?
Cheers, doug


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## Printer2 (Apr 8, 2012)

With the guitar plugged in and with a minimum of volume (can hear hum, buzz, all the little goodies that come with the territory), not quite off, unplug the jack from the amp. The sudden change should be enough to make the amp oscilate if that is indeed a problem (low frequency or high). Watch your speaker to see if you get any motorboating.


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## ed2000 (Feb 16, 2007)

<iframe width="420" height="315" src="Traynor YBA 1, problem maybe? - YouTube" frameborder="0" allowfullscreen></iframe>


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## greco (Jul 15, 2007)

That seems very weird !!

I'm looking forward to seeing what the techs have to say about it.

Cheers

Dave


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## nonreverb (Sep 19, 2006)

That's interesting....as stated by JB welder, it might have something to do with damping. Have you tried it with a different speaker? Is the speaker you're using the correct impedance?


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## loudtubeamps (Feb 2, 2012)

I have seen some pretty weird things over the years while servicing amps.
I am self taught so,cannot explain in electrical terms what I know through over 30 years of practical experience in reparing, designing and building.
I know for a fact that bad,dry caps have the potential to do all sorts of funny things _in a high voltage amplifier_.
Even if the amp is not humming ,it does not mean that the caps are good.
It does not take alot of filtering in some amps to keep them realitively quiet at idle.
Some reading here, especially the article on ESR
cheers, d.
Dissipation factor - Wikipedia, the free encyclopedia
Amp dissolved into hum! [Archive] - The Gear Page


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## WCGill (Mar 27, 2009)

I'd check for dc leakage through a coupling cap and I'd replace the power supply caps.


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## dtsaudio (Apr 15, 2009)

Two things come to mind that have already been mentioned. No damping on the woofer. Possibly the spider is shot. Low frequency oscillation (my best guess). What I think is happening when you play a note, the caps momentarily lose charge (suck out). As they recharge your getting the oscillation. 
I have seen this type of thing before, but usually once it starts to oscillate it keeps going. What's unusual is that it stops on it's own.


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## loudtubeamps (Feb 2, 2012)

greco said:


> That seems very weird !!
> 
> I'm looking forward to seeing what the techs have to say about it.
> 
> ...



Where's WildBill when U neeed em'?


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## ed2000 (Feb 16, 2007)

It's a 2 x 12 cab wired for 16 ohms and both speakers move in unison. This movement also happens on a single 12" speaker cab.


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## loudtubeamps (Feb 2, 2012)

loudtubeamps said:


> I have seen some pretty weird things over the years while servicing amps.
> I am self taught so,cannot explain in electrical terms what I know through over 30 years of practical experience in reparing, designing and building.
> I know for a fact that bad,dry caps have the potential to do all sorts of funny things _in a high voltage amplifier_.
> Even if the amp is not humming ,it does not mean that the caps are good.
> ...


In addition to the obvious as mentioned ......o/p tube screen resistors should be checked.


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## ed2000 (Feb 16, 2007)

Should also say there is occasional crackling independent of volume level.


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## Wild Bill (May 3, 2006)

loudtubeamps said:


> Where's WildBill when U neeed em'?


Definitely change out the filter caps! If they're old why not? Then you don't have to worry about them for another 30 years.

Also, check out the dropping power resistors between the filter caps. They may have drifted very high in value over the years or are breaking down under load. 

If you still have the problem, come back to this thread! You will have eliminated the two most likely causes. We'll have lots of time then to go after the less common ones! lol

Wild Bill/ Busen Amps


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