removing something out of the circuit

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removing something out of the circuit

Postby nyazzip » Thu Feb 05, 2009 2:43 am

this is a total Dummy 101 question, but i have wondered: if you take a pilot lamp or cooling fan or something out of a circuit, do you need to worry about elevated currents in other parts of the amp?
specifically, i have mentioned before that i have a '70s traynor amp which has a big noisy ugly fan installed; i plan on inverting the head and using it "open air" so i'm not worried about cooling. but i am worried about the noisy fan; it is really annoying.
my question is, can i simply clip the fan out of the circuit with no worries, or would i need to attend to something else if i do so? i am just confused as to where that current which was alloted for the fan would go if i clipped the fan out...

similarly, i would maybe like to replace the LED pilots in other amps with incandesent ones(yeah i know, more juice. i just hate the harsh look of leds. and if you turn your head fast enough you can see the 60hz "strobe" effect).
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Postby wyatt » Thu Feb 05, 2009 11:59 pm

That can be clipped out. It runs off the filament feeds from the power transformer, so it's not going to affect plate voltage, or anything else, on the tubes.

Be careful of the amp design before removing the fan. For example a Traynor YBA-1A runs very high plate voltages (650+VDC) to pump a ton of output out of two 6CA7's, running them about as hot as possible without heat sinks. I would want something to dissipate that heat at the chassis for something like that.
Last edited by wyatt on Thu Jun 30, 2011 9:42 pm, edited 1 time in total.
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Postby nyazzip » Fri Feb 06, 2009 1:15 am

thanks!
it just weirds me out that you can remove an electrical demand in one place and it won't reappear in another area or component somewhere......

for the record the amp in question is a ygl-3a, from what i can discern from the schematic i think the plates get maybe 460v. the fan is a really noisy beast; i may install a modern muffin fan which would probably blow equal air for 1/10th the current. when i fire the amp up with thevariac the fan groans and wobbles as the voltage increases, and finally begins to turn at about 90vac. at 120vac it is obnoxiously loud.
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Postby cartoonweirdo » Tue Feb 10, 2009 8:28 pm

Electrical demand is created, not driven. If there is nothing that uses current, no current will flow.

Imagine that electricity is water. There is a huge available amount of pressure (similar to voltage), but unless you open a faucet to send the water TO something (turning on switch or turning up a pot) no flow happens (no current moves). In other words current is actual MOVEMENT of electricity, but voltage is only the potential difference between two areas.

Imagine your power supply as a series of small ponds (the various secondaries), fed from a large reservoir (120V AC), by several pumps (the power transformer).

The rest of the amp can be compared to a gravity feed water supply. If you open a valve all the way a lot of water will flow (current), and the available pressure (voltage) will drop. This is like flushing the toilet while in the shower, or like what happens to plate voltage over a tube rectifier during peaks in current draw. This will only effect the "pond" (winding) from which the "water" (electricity) flows unless there is an engineering flaw (there sometimes are). For example, plate current (and thereby voltage) is liable to fluctuate with demand; but bias and filament current seldom see a very large change in demand, and therefore remain constant.

As far as the analogy goes, water is different from electricity in that electricity will not flow from the source if it does not have a drain (hence demand is created not driven).
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