• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

adding LEDs to amp head

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LED Stuff:

Run them from the tube heater 6.3V AC supply.

LEDS are inherently a diode so will conduct only on one half cycle.

LEDS have a forward voltage drop of around 2.0 volts (blue leds drop a little more and red leds drop a little less, green leds in the middle).

LEDS have very low reverse voltage break down so protect them with a series power diode (like a bog standard 1N4007) with the same polarity as the LED.

add series resitor to limit LED current to say 10 to 15 mA
Calc:
6.3V - 2.0 volts = 4.3 V to be dropped across the resistor.
4.3V / 10mA = 430 Ohms

So for each LEd you add you want a series string:
1/ one side of heater to anode of power diode
2/ cathode of power diode to anode of LED
3/ cathode of LED to current set resistor (390 Ohms for bright, 470 or 560 or even 680 Ohms for less bright)
4/ other side of resistor to other side of heater supply.

If you are using multiple of these wire each alternative "set" to the heater wiring reversed with respect to the 1st so that it conducts on the opposite half cycle of the heater supply.

Cheers,
Ian
 
Heres a cool thing I did with my amp.

http://getchellaudio.googlepages.com/DSC00732.JPG/DSC00732-full.jpg

Its relatively easy to do. I used a small bridge rectifier from the 6.3vac and a current dropping resistor ( seem to recall 4.7k?) and a small BRIGHT blue led. While engraving my name with a dremel was hard to do, it is in theory simple. Carve any design midway into the plexiglass and then stick a LED at each end ( or one in my case) and it will light up the engraved part. I think Hughs and keffner use the same type of thing for their amps.
 
Blue LEDs are best (in my eyes), but here I have enhanced my 50CA10 with yellow LEDs:

An externally hosted image should be here but it was not working when we last tested it.


And this is next project - red LEDs to enlighten a pair of 829:

An externally hosted image should be here but it was not working when we last tested it.


Here I use a massive 10mm led.
I have found out that blue LEDS helps the elctrons move smother from cathode to anode thereby enhancing the sound a lot - firmer bass, crispier treble and much more transparent midrange. My 50CA10 sounds a bit murky due to the yellow light, but I can accept that, just for the look....😀

And a pair of GU50 with blue LEDs:

An externally hosted image should be here but it was not working when we last tested it.
 
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