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Old 18th December 2011, 03:47 AM   #1
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Default power up inrush current limiter - anyone using?

anyone using an inrush current linter on their tube amps. this one is rated at 12 amps. so would it work on my amps that have 10 amp fuses?

4pc Inrush Current Limiting Limiter SG333 12A 5ohms 5 | eBay
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Old 18th December 2011, 05:48 AM   #2
MOER is offline MOER  United States
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Default In rush

Useless for tube amps, check the spec of this device.

Better to use a series resistor bypassed after 1 second by a relay


Steve Mantz

Zed Audio
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Old 18th December 2011, 12:52 PM   #3
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Inrush current limiter

do you want to limit the inrush of B+ ?

if so the solution is a Capacitor Multiplier, this circuit will give slowly way to the B+, so you will see your B+ voltage rise slowly, in accordance with the value of the charge resistor and capacitor value

http://www.el34world.com/Forum/index...ch=27213;image

http://www.el34world.com/Forum/index...ch=27289;image

the added resistor (R2 470K) give the circuit the principal function of Capacitor Multiplier (with relatively little capacitor you'll have high ripple rejection)

without the 470K resistor the circuit helps to reject ripple, but acts more as a slow insertion circuit

as to change that time you can modify the value of the 33k resistor (charge resistor) the time insertion of the schematic with 33k resistor is around 4 seconds

agliostro
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Old 18th December 2011, 02:55 PM   #4
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Hello,
I'm still relatively new to building tube amps but I can lend my experience with these. These were recommended to me by another on this forum and I put them in my Dynaco Mark VI's. The Mark VI is a brute of a power amp and in these amps they have been working just fine for almost two years. I replaced the timed delay relay tubes, which I still have, and haven't had any problems. I put them only on the B+ high voltage which gives you a delay on the B+ until after the bias voltage comes up.

The question I cannot answer is how durable they are. But in two years I haven't had a failure. I'm assuming, like a normal resistor they will fail to open? Where is the risk?

They can be found here: http://www.ge-mcs.com/download/temperature/920_325a.pdf
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Old 18th December 2011, 03:12 PM   #5
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by speakerfritz View Post
anyone using an inrush current linter on their tube amps. this one is rated at 12 amps. so would it work on my amps that have 10 amp fuses?

4pc Inrush Current Limiting Limiter SG333 12A 5ohms 5 | eBay
Have a look here:

NTC THERMISTOR as SOFT START for TUBES


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M. Gregg
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Old 18th December 2011, 04:32 PM   #6
Funker is offline Funker  Germany
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Quote:
Originally Posted by M Gregg View Post
Have a look here:

NTC THERMISTOR as SOFT START for TUBES


Regards
M. Gregg


Hi all,
these thermistors do their job. But I rely more on a delayed Circuit braker in my fuse box. Most of my sockets are fused with 13A curve C circuit breakers. They allow higher inrush currents. Normally you will find B curve circuit breakers in domestic installations. C breakers does have twice inrush capacity than B breakers.

73
Wolfgang
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Old 18th December 2011, 04:46 PM   #7
20to20 is offline 20to20  United States
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A lot of missing details about your amps. Why a 10A fuse, to start with?
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Old 18th December 2011, 05:29 PM   #8
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by 20to20 View Post
A lot of missing details about your amps. Why a 10A fuse, to start with?
I agree,

What current are you drawing from the mains and what wattage are you dissipating in the amp? Remember that a fuse does not blow at the rated current some can be approx 1.5x the value.. I x V = W.
If you are having to use a 10A fuse because of inrush your fault current is going to be quite high. What rating is the mains cable to the amp? With resistive fault you may draw more than the cable can take and not blow the fuse... Reduce the inrush and fuse closer...
Obviously if you switch off and back on you will blow the fuse because the thermistor will be hot and resistance will be low.

EG even if your drawing 500W from the mains with 110V ..4.6A ?
Just for fun measure your AC mains current... Also a Time lag fuse can be used..

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M. Gregg
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Old 18th December 2011, 07:58 PM   #9
AMV8 is offline AMV8  United Kingdom
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Hi
You have not given any data on the amp you want to limit currents on so it is difficult to be specific about your particular application.
However I have used thermisters to limit peak switch on currents in my tube and semiconductor amps for years. I install them in the primrary circuit of the transformer as recomended by national semiconductors and I have never had a problem.
I have bought mine from Rapid electronics and they are 10ohm 12 amp ones.
Don
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Old 18th December 2011, 09:09 PM   #10
Lo_Tse is offline Lo_Tse  Canada
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Quote:
Originally Posted by speakerfritz View Post
anyone using an inrush current linter on their tube amps. this one is rated at 12 amps. so would it work on my amps that have 10 amp fuses?

4pc Inrush Current Limiting Limiter SG333 12A 5ohms 5 | eBay

When I first read about these inrush current limiters (I am a newbie), I thought they are neat devices and all I have to do is put one or two (with the "right" rating) before the main transformer and I am done. Apparently, not so simple. During my search for more information, I found the following site that provide good informations:

http://www.ge-mcs.com/download/appnotes/ntcnotes.pdf
Inrush Current Limiters - Power Thermistors - Home - Ametherm
Epcos's site also has a fairly straightforard application note on NTC.

I am sure there are many more sites on this topic. The ge-mcs site is very detailed and contains all the mathematical descriptions that you want to know but afraid to ask. The Ametherm site is very easy reading and gave a good overview. The Eillot Sound website has a good article on inrush current too.

Overall, based on what I read, a lot of people love the combination of resistor plus a relay by-pass. One can do the same with a thermistor, repalcing the resistor with thermistor. Other like to use some fairly elaborate softstart module. Interestingly, in Nelson Pass's F5 amp article, the PSU that was described contains only 2 CL-60 NTC and that PSU draw huge inrush current due to the big caps used.

Hope these helps

Lo_tse
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