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Hoffman Amps Forum image Author Topic: I should know this...but  (Read 3796 times)

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Offline shooter

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I should know this...but
« on: May 09, 2019, 07:00:29 pm »
with 400 plate, 50mA Ip, the "happy" load ~ 8k

you plug in the wrong speaker and now the load is ~ 2k

Does the tube only get cranky under AC conditions, or do I need to "worry" about the DC conditions also  :dontknow:

thanks as always
dave
Went Class C for efficiency

Offline sluckey

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Re: I should know this...but
« Reply #1 on: May 09, 2019, 07:05:40 pm »
As long as the tube is biased to idle safely it doesn't matter what size load is connected as long as you don't put a signal in. Heck, you don't even need speakers if the amp is just gonna idle.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline shooter

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Re: I should know this...but
« Reply #2 on: May 09, 2019, 07:53:03 pm »
thanks, that's what one of the voices in my head was saying, the other was pretty noisy though  :icon_biggrin:
Went Class C for efficiency

Offline shooter

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Re: I should know this...but
« Reply #3 on: June 18, 2019, 08:02:43 pm »
From PRR in Dude's thread;
Quote
electrolytic caps won't blow-up in 11 seconds

 There is NO "inrush" if the caps charge at power up with NO load ?
If I got that one correct, when load IS applied to full charged caps does the "supply" just "produce" the current as voltage sags, NO "inrush"?

(I think this 1 day Sunshine in 8 is messing with me:)
Went Class C for efficiency

Offline Colas LeGrippa

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Re: I should know this...but
« Reply #4 on: June 18, 2019, 09:10:26 pm »
With everybody ! :icon_biggrin:
Don't miss the Woodstock experience : ''FORTY YEARS AFTER'' at Club Soda,  in Montreal, august the 17th and 18th and october the 27th. Fifteen musicians onstage.  AWESOME !
P.S.: call me Alvin.

Offline dude

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Re: I should know this...but
« Reply #5 on: June 19, 2019, 11:17:24 am »
From PRR in Dude's thread;
Quote
electrolytic caps won't blow-up in 11 seconds


So, no inrush with standby on...?

al
If it ain't broke, don't fix it.

Offline sluckey

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Re: I should know this...but
« Reply #6 on: June 19, 2019, 11:42:36 am »
There is NO "inrush" if the caps charge at power up with NO load ?
The very action of the caps charging will result in an inrush current. Even if nothing is connected to the caps (other than the PT and recto).
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline shooter

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Re: I should know this...but
« Reply #7 on: June 19, 2019, 03:19:50 pm »
Quote
The very action of the caps charging will result in an inrush current

thanks, for some reason I couldn't get there, I seen it as "voltage potential" only, without a current element like static charge, all the electrons to one side, wait for R  :think1:
I did find a good PDF by TI on PS design for dealing with inrush
Went Class C for efficiency

Offline PRR

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Re: I should know this...but
« Reply #8 on: June 19, 2019, 05:21:45 pm »
Are we confusing Volts and Amps?

Consider a Stand Pipe. A variant "water tower".


You build it dry. Then you connect pressurized water supply. The pumps run all day to fill it until the water height equals the supplied pressure. Then you draw water off and the water height drops a little.

In an amplifier often the rectifier comes to life faster than the main load. The 5V4 hots-up and a gush of current flows to the stand-pipe (capacitor). With a saggy rectifier, for a few seconds  the voltage may rise much higher than normal. Then your 6V6es hot-up and suck current. The capacitor voltage drops some.

With tubes, in the 3 to 10 seconds after start-up, the voltage may rise significantly higher than the running voltage you picked your caps on. But 460V on a 450V cap for just these few seconds at start-up won't blow a cap. Yes it would be wise to pick a higher-spec cap, but often we just let it take the hit and some amps run decades with over-volt at start-up.

Offline shooter

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Re: I should know this...but
« Reply #9 on: June 19, 2019, 06:47:43 pm »
 :laugh: I confuse a lot of things  :icon_biggrin:

Quote
the voltage may rise much higher than normal. Then your 6V6es hot-up and suck current

I was pondering without LOAD, ie, standby. I need to read more about caps. My brains assumption was the caps electrons just get sucked to one side until the voltage potential can't move anymore and there they wait til a load happens by, then current happens 
Went Class C for efficiency

 


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