To stupid to use a powersoak - DT25 blown away?

[mikisb]

Hi,

 

this morning i made a really big mistake by connecting a powersoak to my DT25/112: I linked the 8Ohms output of the Amp to the output of the ps and the 16 ohms speaker to the input of the ps. The ps was switched to 16 ohms. So i did everything wrong what i could :huh:  (never play guitar or connect amps before the first coffee) and played a while with mastervolume nearly at 100% and the ps reducing to moderate room level.

This worked for about 5 minutes (i wondered a bit about the relativley harsh sound), than there was no sound anymore and i started to detect my mistake.

 

After turning off the amp and switching on again after a while, it worked some minutes without any problem but than again - no more sound at all - just a very light hum. No, now all connection are ok, ich checked twice ;)

 

I finally measured what i've done - so i used the amp at full power at a load of about 0.7 ohms DC at the 8 ohms output.

I understand that i've blown away my amp cause i was stupid but i don't understand why it works normally for some minutes? When the sound stops, i can't hear something of interest like a relay or something - it just stops sounding. 

 

Has anybody an idea?

 

Thanks a lot and sorry for my english, i'm still learning

 

Michael

 

 

 

[Brazzy]

Awwwww Man that really sucks. Sorry to hear it. I suppose everyone kinda dreads this happening at some point in their life. Hope you can get it fixed easily. have you checked for any internal damage? Like burnt components or blown fuses?

[mikisb]

Hi Brazzy,

 

thanks for feeling with me :)

Yes, I removed the amp out of the combo. As far as i can see - I see nothing. No black marks from burning, no blown fuses. In his last seconds, it smellt a little bit unusual but not much and i can't find the source. Might it help to change the tubes? I still have the old set wich i changed because of a bit noise but i think that, if a tube would be blown away, the amp would'nt work/sound at all??

The powersoak ist 100% OK, but for the moment it's not linked to the amp.

[Brazzy]

I suppose you could try the original tubes to see what happens. It's weird that hear something then nothing. Maybe the transformer has been degraded.

[mikisb]

hmmm - strange: The DT25 is running at livingroom-level now for about 45 minutes - everything works as it should. Voicings, Penthode/Triode......no problem.

Perhaps a heat problem during the first trials, but i was shure that really everything was cooled down after my mistake. So i'll  watch this further and than i will push it a bit with the powersoak.

If everything's fine after, i don't understand what happened. When the tone was going away, there was no noise, no hum, no crackeling and even no relay clicking. Just as somebody hat turned mastervolume down quickly.

If everything's not fine, i'll try to change the tubes and bias them...we will see.

[BillBee]

Don't have a DT or know about the guts but I wonder if it has a thermistor in there that shuts it down.

 

Normally an oopsie like that takes the output transformer out which is repairable.

[mikisb]

sometimes there are wonders :)

After 2 hours i tried again without powersoak  - 45 minutes at moderate level - no problems. Class A/AB - Triode/Pentode, everything worked. Then the hard test with master volume at 75% and Powersoak (correct cabling this time), no problems within half an hour. So a defective hardware becomes more and more doubtful.

In the forum of the powersoak manufacturer (tubetown) someone said to have found something about a protection-circuit of the speaker outputs. He found this on the line6 homepage but without detailed information how this mechanism is constructed. For the moment i hope, that this device protected the poweamp from melting. Perhaps it is a kind of thermistor as you supposed. Perhaps i had a lot of luck today ;)

[spaceatl]

tubes are NOT like transistors....The load will not draw more power...tubes are self-limiting and even if you short it, you are just going to wear the tubes a bit faster. Transistors are nothing like this, so I think you just took a little life off the tubes...mismatch low impedance is not a problem with tube amps...exactly backwards from solid-state.

 

FYI, when you run a tube amp full power with program going thru it, the load will approach 0 ohms all the time...Impedance is not static thing...

 

I am not a fan of resistor based attenuators (powersoaks)...If you lose a resistor, the impedance can go way high and then you can really damage the power section with all the extra flyback voltage....I would suggest you check out a Weber MASS or mini-mass...This is the only way I will attenuate an amp as there is no heat to worry about...Power is dissipated by motion, not heat...

[ColonelForbin]

In the forum of the powersoak manufacturer (tubetown) someone said to have found something about a protection-circuit of the speaker outputs. He found this on the line6 homepage but without detailed information how this mechanism is constructed.

 

Yeah, all I could find to reference the DT25 protection circuit is this:

 

"Speaker jack-sensing provides relay driven output transformer protection circuit"

[spaceatl]

Yeah, all I could find to reference the DT25 protection circuit is this:

 

"Speaker jack-sensing provides relay driven output transformer protection circuit"

 

That has more to do with running with no load at all (forgetting to plug in your cab)...I have not looked at it in detail, but since it's a relay jack sensor, that is NOT going to help if the powersoak fries open and flyback voltage goes thru the roof, because there will still be a plug in the speaker jack and protection would be off at that point.