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Old 29th January 2010, 02:43 PM   #11
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If the tube is damaged, like I made a hoel in the grid or something like that, will it be obvious ?

D.
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Old 29th January 2010, 02:44 PM   #12
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Another question: the value of R5 is critical, or anything around 300 will do ?
It should not make big difference.

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D.
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Old 29th January 2010, 03:29 PM   #13
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R5 should not be critical.
A hole in the plate would be a bad sign. Loss of the getter another. The rest of the damage would be that the grid is warped or broken. It is nearly impossible to see that however. The result would be tube runaway (broken grid) or distortion (warped).

I doubt you did any damage with the filament going cold. For testing purposes you could just blow a small fan on the heatsink until the bigger on arrives.
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Old 29th January 2010, 04:47 PM   #14
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Same thing happened to me when I started testing with 300Bs. The stock HS could manage with the 45's heater requirements, but the 300Bs were too much. It shutdown several times before I figured it out. There were no ill effects. I clamped a squangle to it to get by until I started designing the chassis.

I'm trying to imagine how the heater shutdown could cause R5 to go. The only thought I have is the same as startup: excessive B- voltage. You have 450V caps like I do, so I doubt it.
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Old 30th January 2010, 02:30 PM   #15
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The problem with R5 and the filament are not connected. Probably the resistors I was using were not so good or the had a lower rating then declared. They looked a bit small to me. With the new one I got no problem.
Putting the bigger heatsink fixed the filament voltage shutdown too. I am going to do some serious listening tomorrow.
Now I am running the 300B at 380 V B+ and 69mA bias. The driver are both at 175 V. I found out that one 5842 takes just much more time than the other to go up with the voltage.
I hope I did not damage any other component, as I have 770 VAC, so when I start up I have a peak around 480 V. I am worried about the mosfet. I don't know how they behave if they are broken.
I had the valve tested today and they should be ok. For the damage I was more worried about me passing 130 mA when the max rating is 100mA, although it was for a very short time.

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D.
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Old 30th January 2010, 04:15 PM   #16
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MOSFETs are a little weird in how they can fail. Most silicon is working or shorted or popped. Large FETs can be overloaded where damage occurs to the junction but the FET still functions to some degree. I've done this in a regulator circuit and usually the operating point becomes unstable when that happens. In the case of this design I would expect the output tube bias to drift a lot. If the bias is stable, the FETs are probably fine.

As far as overloading the tube briefly...I wouldn't worry about it. Tubes can handle short durations outside of their safe operating conditions. One nice thing about their physical size, I guess.
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Old 31st January 2010, 11:14 AM   #17
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So after one morning of listening, I do not think I blowed anything. The listening is very plesant.
Due to the higher voltage of the power supply, I am running at 380 V B+, that put around 365 V on the plates. The B- is -70V. The drivers have 175 V on the plate.

What I noticed, is that this amp needs a much higher signal level compared to the Simple SE. With my CD player I could turn the volume knob to the maximum and it still was not to loud. My speakers are not the most efficient ones.

Is it like this also with your amps ?

Best Regards,

Davide
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Old 31st January 2010, 02:10 PM   #18
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Yes, the Tubelab SE has lower gain.
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Old 31st January 2010, 04:12 PM   #19
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The Simple SE has a lot of gain, especially in UL mode. Mine will go well into clipping at about 80% of "line level" signal. The Tubelab SE can take 100%, depending if I am running 45s or 300Bs. What tubes do you have in the SSE? I found that the SSE with EL34s in triode would start clipping at about the same volume level as the TSE with 300Bs, but the SSE still needs less input to get there.
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