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Old 18th January 2011, 05:16 PM   #31
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Do welding machines and car battery chargers comply to UL?
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Old 18th January 2011, 06:08 PM   #32
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Unfortunatly a lot of transofrmers do not have UL certification, or any certification for that matter.

I'm trying ot understand how all the referenced sections and clauses relate.
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Old 18th January 2011, 07:24 PM   #33
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Quote:
Originally Posted by Wavebourn View Post
except 6C17K-B Click the image to open in full size.

To prevent damage of output transformer in parallel with output tubes in push - pull amps should be soldered high voltage high frequency SS diodes, in reverse polarity. Diodes from TV horizontal flyback are fine.
Au contraire, even transmitter valves have mechanical resonances of the least supported part (grid) - however probably not in the audio range! I collated some interesting info at Microphonics

The freewheeling diodes only clamp one half winding below 0V, and rely on good coupling and low leakage inductance of other half winding (a reasonable assumption for OT's at lower frequencies, but maybe not for transients due to say a fuse blowing).

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Old 19th January 2011, 03:22 AM   #34
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Quote:
Originally Posted by Wavebourn View Post
Do welding machines and car battery chargers comply to UL?
Since my Hobart has cSAus, I suspect they could also carry cULusa .

My battery charger is older and is UL listed.
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Old 19th January 2011, 04:01 AM   #35
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Quote:
Originally Posted by trobbins View Post
Au contraire, even transmitter valves have mechanical resonances of the least supported part (grid) - however probably not in the audio range! I collated some interesting info at Microphonics
6S17K-V is planar triode that worked in rockets on acceleration up to 500G, and up to 10g vibration. I doubt you can register any microphonic in audio band. I could not, I have breadboards of mic pre and MC phono preamp.

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The freewheeling diodes only clamp one half winding below 0V, and rely on good coupling and low leakage inductance of other half winding (a reasonable assumption for OT's at lower frequencies, but maybe not for transients due to say a fuse blowing).
Did I wrote that it is for PP output stage? What fuse blowing if the question was about disconnected speaker? And how fuse blowing can affect PP transformer?

For SE amp one more diode + powerful Zener is needed.
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Old 19th January 2011, 06:36 AM   #36
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Yes well the phrase all valves are microphonic was meant to be a reminder, given kevinr's comment, that although you may not 'hear' a valve being microphonic in your amp, it will be contributing a microphonic signal (howefver small) due to vibrations given the generic construction of valves. Even the frame grid structure will vibrate. The point being not to gloss too liberally over the issue, even though it was not the main post topic.

Quote:
To prevent damage of output transformer in parallel with output tubes in push - pull amps should be soldered high voltage high frequency SS diodes, in reverse polarity.
I think you did target PP configuration. Yes I should have used disconnected speaker as the more relevant example of a transient. Whether a step change in load, or a fuse blowing, if there was current flowing in the OT primary at the time of the transient then all that energy has to go somewhere. I'd anticipate one winding end is nominally clamped (a freewheeling diode, or zener, or conducting tube, or B+ if both PP's are in cutoff), the other end of the winding flys in voltage (mainly limited I suggest by whatever parasitic capacitances are around). It's a good topic to discuss and worth appreciating how it may impact the commonly used circuit configurations.

I suggest an SE configuration is inherently lower risk wrt OT insulation breakdown from speaker side transients.

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Old 28th February 2011, 08:28 PM   #37
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Originally Posted by kavermei View Post
In the end, tube amps can stand quite some amount of abuse, so I'd be surprised if any lasting damage is done in this case.
The Russians stuck to valves in their planes for a very long time as they are immune to EMP (electro magnetic pulse) from nuclear explosions.
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