[miglto]

Tubes in a power amp... Can the damage the output transformer or speakers if they go bad?

Specifically, I have a Kondo Ongaku (211 power output tubes).

Thanks!

Miguel

[FullRangeMan]

Yes it can damage if your amp dont have fuse protections and more etc
Just the output plate hi voltage supply in the 211 tube usually is 900V DC.

[miglto]

Understood... But does this actually happen? The amp does have a fuse.

[Ericus Rex]

Morgan Jones in his Valve Amplifiers book has a very good and lengthy section on transformers and what can go wrong with them.    I highly recommend that exhaustive tome if you don't already have it.  Apparently, OPTs can be damaged before fuses blow if the conditions are right.

[FullRangeMan]

But does this actually happen?
There is no many 211 amps on the market today and customers, but it usually happen with sino tubes and those 75W 211 versions, the 100W plate are more robust.

If your 211 tubes are military as WE,RCA,GE etc they are more reliable.
I just know one catastrophic case, here a AC member was using a sino 75W 211.
Unfortunately US 211 seems already finish, who did not buy not buy anymore.
 
If your amp have just 1 fuse it is the mandatory power supply fuse, not a output fuse, in this case dont use 75W 211s, as all 211 amps are built expecting use 100W 211 tubes.

[miglto]

I have GE VT4C 211 tubes. Came with the amp (about 6m old). Yes, it's only one fuse for the power supply, not the output stage.

[Ericus Rex]

Morgan Jones also explains in the same section why so many 211s fail prematurely.

[Quiet Earth]

Yes, it's only one fuse for the power supply, not the output stage.

I don't know specifically about the Kondo designs, but many of the Audio Note UK designs have a second fuse under the hood. Typically, if you remove the top plate screws the copper cover and the transformer covers will come off together and expose a second fuse. The second fuse is the high voltage B+ fuse for the power tube.

Again, I don't know if this applies to your amp, but it is something you should probably investigate just so you know.

I just know one catastrophic case, here a AC member was using a sino 75W 211.
Unfortunately US 211 seems already finish, who did not buy not buy anymore.

I think Rollo's 211 amp melted down due to a faulty output transformer, not a faulty tube. (Not 100% sure, just going from memory. He will probably chime in here.)

[FullRangeMan]

Morgan Jones also explains in the same section why so many 211s fail prematurely.

Seems a interesting book, this is the book you are mentioning??
http://www.amazon.com/Building-Valve-Amplifiers-Morgan-Jones/dp/0750656956

[FullRangeMan]

I think Rollo's 211 amp melted down due to a faulty output transformer, not a faulty tube. (Not 100% sure, just going from memory. He will probably chime in here.)

Rollo was using a sino 75W 211, even some USA 211 models are 75W plate.

Seems MIGLTO would email to the factory to clear this issue, surely they will help in this prevention, since the hi price of this model.

[FullRangeMan]

I have GE VT4C 211 tubes. Came with the amp (about 6m old). Yes, it's only one fuse for the power supply, not the output stage.

Good news, if this is your 211 it had a 100W plate:
http://www.tubecollector.org/vt-4-c.htm

[Ericus Rex]

Seems a interesting book, this is the book you are mentioning??
http://www.amazon.com/Building-Valve-Amplifiers-Morgan-Jones/dp/0750656956

That's his follow-up book on construction tips.  This is the book I'm referencing:

http://www.amazon.com/Valve-Amplifiers-Third-Morgan-Jones/dp/0750656948/ref=sr_1_5?s=books&ie=UTF8&qid=1400972648&sr=1-5&keywords=morgan+jones+valve+amplifiers

[FullRangeMan]

That's his follow-up book on construction tips.  This is the book I'm referencing:

http://www.amazon.com/Valve-Amplifiers-Third-Morgan-Jones/dp/0750656948/ref=sr_1_5?s=books&ie=UTF8&qid=1400972648&sr=1-5&keywords=morgan+jones+valve+amplifiers

Thanks. There is a 4th editon, it look better with more stuff:
http://www.amazon.com/Valve-Amplifiers-Fourth-Morgan-Jones/dp/0080966403/ref=la_B001HCUX52_1_1?s=books&ie=UTF8&qid=1400971334&sr=1-1#reader_0080966403

[miglto]

Morgan Jones also explains in the same section why so many 211s fail prematurely.

Yes, that's my tube. On the 100W spec, if you look at the GE VT-4C specsheet, you'll see that the 100W spec is for Class-B operation. For Class-A operation it is 75W. I think there's a fair amount of confusion out there regarding this spec. Even the cheap Shunguangs have 75W dissipation in Class-A as far as I can tell.

Miguel

[miglto]

Rollo was using a sino 75W 211, even some USA 211 models are 75W plate.

Seems MIGLTO would email to the factory to clear this issue, surely they will help in this prevention, since the hi price of this model.

Yes, that's my tube. On the 100W spec, if you look at the GE VT-4C specsheet, you'll see that the 100W spec is for Class-B operation. For Class-A operation it is 75W. I think there's a fair amount of confusion out there regarding this spec. Even the cheap Shunguangs have 75W dissipation in Class-A as far as I can tell.

As for emailing the factory, I assume that the GE VT-4C are up to spec. I don't think Audio Note Kondo Japan replies to email anyway...

Miguel

[FullRangeMan]

As for emailing the factory, I assume that the GE VT-4C are up to spec. I don't think Audio Note Kondo Japan replies to email anyway...

Miguel

I think AN must serve their customers in an exceptional way because the extremely high price of their products.
If I did the insanity of buying a unit of this price I would want a red carpet welcome.

[miglto]

I think AN must serve their customers in an exceptional way because the extremely high price of their products.
If I did the insanity of buying a unit of this price I would want a red carpet welcome.

They are pretty good, and so is their dealer in NYC. You get what you pay for (to some extent).