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Old 2nd June 2011, 08:43 AM   #21
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Quote:
Originally Posted by prairiemystic View Post
I am talking about people using several hundred uF filter caps on a C-input filter with 5U4's. The power-up flash from cathode-stripping is impressive.
That's just plain insanity. They got away with it back in "the day" because they were counting on a tech-illiterate public to not know this, and you could get a new 5U4GB at just about any pharmacy, grocery, convenience store, etc.

Quote:
The 5U4-GB datasheet (pdf) is a bit confusing. Maximum ratings:
"Transient peak plate current per plate, maximum duration 0.2 second = 4.6 amperes"
"Steady-state peak plate current of 1.0 ampere maximum per plate." The graph shows 120V drop @ 1A... I call that a supernova
Nothing confusing about it. That 4.6A for 0.2 secs is the "hot switching" limit. This would apply if you had a standby that disconnected the HV, but left all heaters (including the 5U4) hot. Doesn't apply if you're not doing this.

The 1.0A rating is the Isurge. When I did a design that used this type (because I had a PTX that overvolted badly when used with Si diodes) I needed to drop 100V. An Isurge of about 800mA did that, and a 34uF reservoir capacitor came quite close to making Isurge= 800mA. The forward voltages aren't out of line here, and are typical for a vacuum diode. Since I have the Isurge comfortably under the max limit, I haven't had any problems with the "Realistic Lifetime" 5U4GB I picked up, unused.

"120V drop @ 1A... I call that a supernova "

It only seems that way if you're more used to Si diodes with their 0.7V forward voltage. Not atypical at all for hollow state.
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Old 2nd June 2011, 02:42 PM   #22
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Default So, how do you measure Dynamic Response, or lack of?

I've read numerous posts and articles about this topic. Like with other things that impact sound quality, I think it's important. Just listening seems to a bit allusive and subjective.

Can a PS's ability to respond to dynamics be measured? How?

I took an amp (SE 5W 6BQ5) to a friends house for him to evaluate. Dynamic response was one of the topics on my list. We looked at changes in the DC voltage value at the ripple level while playing music. Is the way to test?
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Old 2nd June 2011, 11:29 PM   #23
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Quote:
Originally Posted by Troncones View Post
I've read numerous posts and articles about this topic. Like with other things that impact sound quality, I think it's important. Just listening seems to a bit allusive and subjective.

Can a PS's ability to respond to dynamics be measured? How?

I took an amp (SE 5W 6BQ5) to a friends house for him to evaluate. Dynamic response was one of the topics on my list. We looked at changes in the DC voltage value at the ripple level while playing music. Is the way to test?
Sounds OK but in a SE amp as all pure class A amps the PS's ability to respond to dynamics is only determined by the quality of the last capacitor i the PS. The average current draw is constant (well even harmonics will make it raise somwhat) and the last cap should be sized to take care of signal current down to lowes frequency of interest. And it should be poperly by passed with a high quality smaller cap to minimise effects of ESR and ESL at higher freq.

/Olof
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