power consumption

can someone enlighten me as to what a 200 watt amp(such as the st70) would use as far as electrical watt/power consumption at various levels of loudness? i assume 200 watts is idle with no signal to the output. i know 3 amp fuse and 117 volt, pretty much indicates the protection at 350 watts going by ohms law, so is that to say it will only consume up to 350 watts if i were blasting it full on?

This has recently been discussed here : https://dynacotubeaudio.forumotion.com/t3739-simple-question-how-many-watts-does-my-vta-st-70-consume

ahhhh. ok, thanks Peterh. so its safe to assume that the 190 watt labeling is basically the full load watt use.
so then a 3 amp fuse is over rated by at least 45%.
on the cusp,but i should be ok putting a 2 OR 2.5 amp fuse in there then for added protection.
ive been getting some voltage fluctuations lately, due im sure from the tornadoes we had a bit ago here in ct, and im thinking there is some collateral power damage that hasn't fully reared its ugly head. i dont want my amp to be subject to stray rebel electrons.lol

dmagazz wrote:ahhhh. ok, thanks Peterh. so its safe to assume that the 190 watt labeling is basically the full load watt use.
so then a 3 amp fuse is over rated by at least 45%.
on the cusp,but i should be ok putting a 2 OR 2.5 amp fuse in there then for added protection.
ive been getting some voltage fluctuations lately, due im sure from the tornadoes we had a bit ago here in ct, and im thinking there is some collateral power damage that hasn't fully reared its ugly head. i dont want my amp to be subject to stray rebel electrons.lol

One must consider the turn-on surge, that's why 3A slow-blow ( at 110V) is used.
You shoud consider a device that breaks power when power is interrupted, it has
been shown several times here ( some kind of ground-fault interrupter with manual
reset )Maybe that should be a frozen topic on this forum ?

Yup - manual reset required, so it provides protection against those BLIP BLIP overloads from intermittent power that doesn't provide time for the amp to drain properly.



TRC 90033 Shockshield

yep, i do know of the power on surge.but id wondered if 2.5 is enough for that.and thats a good idea.(the plug in/socket breaker) ive not seen many things that have been discussed. but somehow more often than not when i use the search it comes up dead.

.

actually, the rack my amp is plugged into has a surge protector and 15 amp push reset breaker in it.

Big difference between a standard power strip with surge protection and these adapters is the manual reset. If your house blinks and the strip doesn't trip (which it won't) you still get a shiny new slug of power pushed into an amp that hasn't had time to discharge the caps properly. That can reek all sorts of havoc.

so those trip at just a tweak of currant flux? hmm
just checked it out actually. didn't realize the link before.
gfci adaptor. ill pick one up and put it on the main to the rack.
my harman kardon 730 is rather delicate too.

OK - I will give my patented mini-rant on fusing electronic equipment:

a) Slow-Blow fuses (those with a spiral-wound element on a small ceramic stick inside) are the invention of the devil, and fit only to protect real-estate, not the equipment they serve. If one reads the specifications on these wretched beasts, they are able to tolerate a 100% overload for 10 seconds, and a 20% overload pretty much indefinitely. So, your 3A fuse will pass 6 A for 10 seconds. And, 3.6 A for as long as it takes to cook a transformer or two.

b) Yes, tube equipment has a significant starting surge before the filaments heat up - and that surge may be as much as 200% of the standing load.

c) So, if the standard operating load is 190 watts, and the surge as much as 380 watts for about a second, and one is operating at 120 V at the wallplate, technically, the fuse must be able to take ~3.2A for about a second.

d) After which, it really only needs to be able to handle about 1.6 A.

Now, there is something called a Dual Element Fuse. It is able to tolerate very high loads very briefly, such as motor starts and similar applications. These are available in fractional amperage values down to 1/10A and up to whatever. These fuses have the ability to actually protect the equipment where a standard fast-blow fuse big enough to withstand the starting surge, or a conventional slow-blow WILL NOT.  These fuses are expensive, but not relative to a transformer. What happens is that they behave as a slow-blow for the start, then as a conventional fast-blow during operation. NOTE: These fuses  do not like to be short-cycled.

What I do 'at home' is determine the exact load of the equipment at peak, and then size the fuse to that value. I am running my Vintage 70 on a 2A MDQ fuse.

https://www.mouser.com/datasheet/2/87/Bus_Elx_DS_2044_MDQ_Series-335854.pdf    


Note that fuses are wearing parts - and will sometimes blow spontaneously - especially if sized close to the actual load (as they should be).

Peter W,
Do you know if this would also be the appropriate fuse for a VTA ST 70?

https://www.mouser.com/datasheet/2/87/Bus_Elx_DS_2044_MDQ_Series-335854.pdf

Dave_in_Va wrote:Peter W,
Do you know if this would also be the appropriate fuse for a VTA ST 70?

https://www.mouser.com/datasheet/2/87/Bus_Elx_DS_2044_MDQ_Series-335854.pdf    

It would, in the correct range. I happen to have an iso-variac with a very fine-pitch ammeter that allows me to get the precise (and accurate) steady-state power draw. And from that, I size fuses.

https://forums.qrz.com/index.php?attachments/img_9297-jpg.394181/

So without an "iso-variac with a very fine-pitch ammeter" I can't really tell if the 2 amp MDQ fuse is the one that would work for my VTA 70, right? I'd just be gussing?

https://www.mouser.com/Search/Refine.aspx?Keyword=2A+MDQ+fuse

Dave_in_Va wrote:So without an "iso-variac with a very fine-pitch ammeter" I can't really tell if the 2 amp MDQ fuse is the one that would work for my VTA 70, right? I'd just be gussing?

https://www.mouser.com/Search/Refine.aspx?Keyword=2A+MDQ+fuse

Do you have a VOM with an AMPS setting? IF you put that in series with your amp and the receptacle - which should be good enough. Hot side, and done with care.

You can also measure across a fixed resistor and calculate.

peter,thats exactly what i put in my dynaco. an mdq 2a. i didnt think of the variac + meter thing before, i modded my variac into a small contained unit that give's me live amps and volts out(2 separate meters-both fused). i can plug in my st70 and see EXACTLY how many amps and volts its drawing as its running.

Peter W. wrote:OK - I will give my patented mini-rant on fusing electronic equipment:

a) Slow-Blow fuses (those with a spiral-wound element on a small ceramic stick inside) are the invention of the devil, and fit only to protect real-estate, not the equipment they serve. If one reads the specifications on these wretched beasts, they are able to tolerate a 100% overload for 10 seconds, and a 20% overload pretty much indefinitely. So, your 3A fuse will pass 6 A for 10 seconds. And, 3.6 A for as long as it takes to cook a transformer or two.

b) Yes, tube equipment has a significant starting surge before the filaments heat up - and that surge may be as much as 200% of the standing load.

c) So, if the standard operating load is 190 watts, and the surge as much as 380 watts for about a second, and one is operating at 120 V at the wallplate, technically, the fuse must be able to take ~3.2A for about a second.

d) After which, it really only needs to be able to handle about 1.6 A.

Now, there is something called a Dual Element Fuse. It is able to tolerate very high loads very briefly, such as motor starts and similar applications. These are available in fractional amperage values down to 1/10A and up to whatever. These fuses have the ability to actually protect the equipment where a standard fast-blow fuse big enough to withstand the starting surge, or a conventional slow-blow WILL NOT.  These fuses are expensive, but not relative to a transformer. What happens is that they behave as a slow-blow for the start, then as a conventional fast-blow during operation. NOTE: These fuses  do not like to be short-cycled.

What I do 'at home' is determine the exact load of the equipment at peak, and then size the fuse to that value. I am running my Vintage 70 on a 2A MDQ fuse.

https://www.mouser.com/datasheet/2/87/Bus_Elx_DS_2044_MDQ_Series-335854.pdf    


Note that fuses are wearing parts - and will sometimes blow spontaneously - especially if sized close to the actual load (as they should be).

The absolute Gospel Truth.  Amen!

ok with my variac / DC voltmeter( i divide by.636)to get ac/amp meter, i have a switch on it as well so i can leave the variable  setting and just turn it on, so i turn it on at 100%, it goes to 1.9a, down to .8 amps, warms up and goes to 1.6, i ran it for a couple hours, it stayed 1.6 all the way up to when i started to push it. when the bass gets hard and heavy, the amp meter shows it bump the needle with the bass thumps as expected,but it never went over 1.8. so its safe to say a mdq 2a fuse is right on the cusp when its pushed. i like it
here is the variac unit i made a couple years back.

This is what the power-monitor my VTA ST-120 is saying this morning (and this is very typical)

as id expect, the 120 uses a bit more than my st-70,it doesn't seem to go past 1.8a with a sweet sounding load. im rolling on a safe mdq 2a fuse.