Symptoms of a Blown Mosfet (BADA PH-12)

[Territhemayor]

I hear a ton about blowing a Mosfet, specifically about changing tubes to frequently. If I have blown a mosfet, how would I know? I usually wait at least 5 hours before changing tubes (with the power off) But I only waited an hour and a half before swapping this time. Now my Right channel has a distinctly different sound (could be the tubes)

Thanks

 

[jona.p]

I have never heard of blowing mosfets and my experience with tuberolling is very limited. But;

Quote:

Ø Turn the power off and WAIT FOR THE TUBES COOL before pulling them out! The tubes, especially the 6080, get very hot! You will get burned if you grab them. Also, it takes a little time for all the high voltages to decay after the power is turned off, and you don't want to pull any tube with live voltage on it.

Quoted from some tuberolling PDF for the HA-2 from Wheatfield Audio. Thats the only thing that document says about waiting before changing tubes;p.

Maybe try the old tubes again? See if its still there, or wait for the tubes to settle or something. Thats what people keep telling me anyhow

.



Goodluck!

 

[Icarium]

Quote:

Originally Posted by Territhemayor /img/forum/go_quote.gif I hear a ton about blowing a Mosfet, specifically about changing tubes to frequently. If I have blown a mosfet, how would I know? I usually wait at least 5 hours before changing tubes (with the power off) But I only waited an hour and a half before swapping this time. Now my Right channel has a distinctly different sound (could be the tubes) Thanks

That's pretty hardcore of a wait. I don't tube swap often but I've never waited more than 5 minutes and its never affected the sound either way.

 

[Dept_of_Alchemy]

It's most likely the tubes, have you tried swapping it back and see if the sound is the same?

 

[bhd812]

Quote:

Symptoms of a Blown Mosfet (BADA PH-12)

1. Feeling elated, feeling in "overdrive", feeling "high", feeling "wired ", and sometimes simply feeling very angry and irritable . example would be if you go to power up the amp and it responds with a "No!!!!".


2. Much more energy than usual. if the Volume level seems higher then usual being at the same spot on the volume pot.


3. Much less need for sleep than usual (many Mosfet have trouble sleeping, but sleeping significantly less than usual and not missing such sleep or feeling unusually tired are significant indicators of being high). the amp does not want to turn off.


4. More self-confidence than usual. The amp thinks maxed out sp's or B52's stand no chance in a sound quality comparison.


5. More social confidence and extroversion than usual, such as more confidently initiating conversation with strangers and with other people in social situations. the amp wants to talk with your headphones out of the regular work place. or maybe the amp is caught browsing the net for better tubes.


6. Making more conversation than usual. when you listen to a well known song you hear micro details you never heard in the song before or in the audio rig before.


7. Making more telephone calls than usual. you start to see calls to 1-900-grado69 on your monthly bills.


8. Feeling more creative than usual, with new ideas about future plans and ways to make money. (Often these ideas have potential undoubtedly, but the person involved is unable to appreciate the real problems or risks associated with such new, positive ideas.) when your listening to your amp and you hear the singer say "lets list those headphones in the f/s section now." randomly out of nowhere.


9. Driving at higher speed or more aggressively than usual. does your music sound like it was sung by the chimp munks randomly?


10. Having increased sex drive and perhaps being more flirtatious or more sexually active than usual. out of nowhere you think Barry White and Marvin Gaye would sound amazing on this amp.


11. Spending money more freely than usual. All the amp wants is upgrade and upgrade.

If you think your mosfet is Blown and you want to seek the best help then maybe post this topic on this site...

 

[spookygonk]

I got up to #7 before I realised it wasn't a serious(ish) post. Do'h!

 

[SK138]

Hahaha...Billy was probably drunk partying with Santa's helpers when he wrote that

To OP...if you blow a MOSFET, you probably hear a channel imbalance. I think the recommend hours when changing tubes on that amp is about 24 hours.

Quote:

Originally Posted by spookygonk /img/forum/go_quote.gif I got up to #7 before I realised it wasn't a serious(ish) post. Do'h!

 

[sacd lover]

Quote:

Originally Posted by Territhemayor /img/forum/go_quote.gif I hear a ton about blowing a Mosfet, specifically about changing tubes to frequently. If I have blown a mosfet, how would I know? I usually wait at least 5 hours before changing tubes (with the power off) But I only waited an hour and a half before swapping this time. Now my Right channel has a distinctly different sound (could be the tubes) Thanks

Blown MOSFET's are a chronic problem with the Bada. You can only avoid the problem by waiting a considerable time before switching tubes. Why? The tube front end holds a charge that can discharge when the tubes are pulled and fry the MOSFET. You need to be sure that the stored energy has dissipated before switching the tubes; usually several hours to be sure .... according to Bada owners. People are comparing tuberolling this amp with pure tube amps and that is not a valid comparison.

The term blown can refer to destroyed or damaged. If the MOSFET is damaged you will hear sound that is distorted and/ or lower in level, hum and noise.

 

[Roam]

Quote:

Originally Posted by sacd lover /img/forum/go_quote.gif Blown MOSFET's are a chronic problem with the Bada. You can only avoid the problem by waiting a considerable time before switching tubes.

Waiting will only do so much as the dielectric absorbtion of the capacitors will cause them to "self-charge" after the tubes cool down and stop conducting. This is why bleeder resistors are a must with high voltage capacitors, not surprisingly the Bada doesn't have them.

 

[drarthurwells]

I haven't blown a mosfet since I started waitng 20 hours or more (with the amp off all that time) before taking a tube out.

Also I have settled on the Ken Rad GT (with staggered plates, before GE made them under the Ken Rad name) in front and two Shuguang Chinese in back - a great high resolution and natural timbre combo.

Symptoms of blown mosfet is greatly reduced volume and hardly any volume on the blown mosfet side.

 

[tourmaline]

Quote:

Originally Posted by drarthurwells /img/forum/go_quote.gif I haven't blown a mosfet since I started waitng 20 hours or more (with the amp off all that time) before taking a tube out. Also I have settled on the Ken Rad GT (with staggered plates, before GE made them under the Ken Rad name) in front and two Shuguang Chinese in back - a great high resolution and natural timbre combo. Symptoms of blown mosfet is greatly reduced volume and hardly any volume on the blown mosfet side.

I only wait 30 mins and i don't have blown a mosfet at all! But i have resistors attached to the caps and these might act as bleeder resistors??!!

Great to hear art that you found another great tube combo. Stuart and i are still experimenting with tubes though.

Do yourself a favour and get active cooling for the bada, it makes it sound much better.