I am not of a different opinion, I just did not mean _slow_ charge of "electrolytes". Slow charge and time delay are completely different things. I use resistor in primary exactly for "slow charge of electrolytics", limiting inrush current. After electrolytics had been charged up to 70% of the voltage the relay shorts the resistor and stays on until power is not removed and electrolytics discharged.
I have to sharpen my written English.....the concept was:
By the delay of the +B voltage the in-rush current limiter was implied.......
During the delay-period the idea was to have "a slow charge of the capacitors" and that the heaters during the same delay had reached max. before the full +B voltage was connected.
I received boards today, smallest one is for slow start/surge charge limiter. Bigger one is for rectivier. Originally it will rectify 400+400V. The biggest one contains rectifiers for negative bias and filament of preamp tubes, also voltage stabilizers for -72V (bias), +12.6V (filaments), +270V (screen grids) and +400V (preamp and driver).
Also, the longest board will have on it couple of 20 uF film caps, shunt for 800V B+ power. It contains star ground and all output voltage pads.
Also, the longest board will have on it couple of 20 uF film caps, shunt for 800V B+ power. It contains star ground and all output voltage pads.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It shunts 800V B+ on AC by 10 uF film cap, directly to the star ground. Such way output tubes are powered as if from 10 uF film caps (20 uF/2), but rectified AC is actually smoothed by 470uF/2 electrolytic cap + 10uF film.
All power supplies at their outputs are interconnected at the star ground. Such "zero volt reference" eliminated the "sonic difference" between rectifiers and power cables.
To refresh this thread, Ametherm now has a calculator for determining the appropriate inrush current limiter.
You'll also need a good idea of the steady state current so as to not fry the current limiter.
https://www.ametherm.com/blog/inrush-current/calculate-inrush-current-three-steps
You'll also need a good idea of the steady state current so as to not fry the current limiter.
https://www.ametherm.com/blog/inrush-current/calculate-inrush-current-three-steps
Imho it is unwise to refer to a generic NTC calculator without proviso's on where such a calculator is lacking for specific amplifier type applications. One issue is that the amplifier would not have a a unity power factor input such that mains current is just related to steady state power and voltage and a nominal transformer efficiency. Another is that the filter capacitance is on a secondary winding and needs to be translated to the primary voltage. Another is that breaker or fuse tripping due to a peak in-rush current is quite a technical aspect and requires assessment of the trippable device. Another is the caution that adding an NTC just for kudos without a good technical reason is a hazard as it requires fitting a new part to the mains primary circuit and to do that in a safe manner due to the operating temperature of the NTC.
No problems, look for "power supply protection amplifier"
e.g. https://www.ebay.com/sch/i.html?_fr...kw=power+supply+protection+amplifier&_sacat=0
You will have to look at the pictures and documentation what kind amplifier they're for - they might be for solid state in which case the NTC's are too low a value. You also will need to look if they're using NTC's since some of them use ordinary resistors.
You also need to filter out those that are used for the speakers.
Good luck!
e.g. https://www.ebay.com/sch/i.html?_fr...kw=power+supply+protection+amplifier&_sacat=0
You will have to look at the pictures and documentation what kind amplifier they're for - they might be for solid state in which case the NTC's are too low a value. You also will need to look if they're using NTC's since some of them use ordinary resistors.
You also need to filter out those that are used for the speakers.
Good luck!
I detect more paranoia generated around tube amps, for whatever reasons.
My vintage 1963 RCA Victor TUBE console stereo, containing 18 tubes, never had the need for a NTC thermistor device OR some form of delay.
In fact, it's still operating on its original 5AS4 rectifier, and the majority of its other tubes are original, dated coded 2/62.
I don't have the least amount of worry/paranoia when I turn the blasted thing on, I just enjoy the lovely sounds of music that it produces.
I don't get all the hype about delays and such, where did it all stem from?
Internet blabber causing widespread fear?
My vintage 1963 RCA Victor TUBE console stereo, containing 18 tubes, never had the need for a NTC thermistor device OR some form of delay.
In fact, it's still operating on its original 5AS4 rectifier, and the majority of its other tubes are original, dated coded 2/62.
I don't have the least amount of worry/paranoia when I turn the blasted thing on, I just enjoy the lovely sounds of music that it produces.
I don't get all the hype about delays and such, where did it all stem from?
Internet blabber causing widespread fear?
Perhaps if someone can do a direct link to protection module that they think is relevant and that has 'documentation' then that could be a good starting point for forum discussion.
Imho I'd anticipate that many reading this thread are doing so as they don't have a good technical awareness of how to select an NTC, or why the NTC may (or may not) be of benefit to them other than because they have read other threads and get a warm fuzzy feeling that including an NTC must be a good thing.
Imho I'd anticipate that many reading this thread are doing so as they don't have a good technical awareness of how to select an NTC, or why the NTC may (or may not) be of benefit to them other than because they have read other threads and get a warm fuzzy feeling that including an NTC must be a good thing.
IMHO If readers can not work out the advantages/disadvantages and/or determine the correct value of NTC's then they have not sufficient basic knowledge to work on tube amplifiers.
After all one is working with lethal voltages.
It may sound harsh but the information is sufficient to work out what is needed.
After all one is working with lethal voltages.
It may sound harsh but the information is sufficient to work out what is needed.
With due respect - a properly sized NTC can result in a fuse that is close to the actual power consumption of the amplifier offering better protection if something fails internally. A smaller fuse may save your mains or output transformer.
Adding NTC's can extend the life of some hard to obtain NOS tubes.
I disagree.
I've already added a 2.5A line fuse to the console, as well as restoring-customizing it to my liking.
It never needed a thermistor throughout it's 50 year life, and since most of its original tubes are still healthy, including the rectifier that's powering 17 tubes, I don't feel the need to mess with success.
But if ever needed, I've got plenty of NOS replacement tubes in stock.
By the way, I see you're new on here, so just to let you know, I'm a retired-after-45+ years professional audio/video service tech.
I think by now I pretty much know my trade.
Just because I'm newly registered does not mean that I am new to tube audio/TV. Got over 60 years here and TV's in the past often had NTC's and so did the el cheapo stuff that did not have a transformer. Perhaps in the USA things were different from where I came from.
Unfortunately not many EL506 are around any more so have to squeeze an as long as possible life out of them. I've my doubts about those EL506 in Vietnam that are advertised on eBait for some ridiculous price. (And not to forget that I want to keep my Lowther amplifiers original.)
Unfortunately not many EL506 are around any more so have to squeeze an as long as possible life out of them. I've my doubts about those EL506 in Vietnam that are advertised on eBait for some ridiculous price. (And not to forget that I want to keep my Lowther amplifiers original.)
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