changing the color tubes emit

i recently saw somewhere a dynaco amp that could change the color that the tubes emitted. does anyone out there know how this is done?

it was on ebay and it was a st-120 item # 150700540959. someone asked how he did that and he answered "very carefully" would really like to know how to do that . nice effect

I think that they use led's to change the tube colors. I know you could mount an led in a 9 pin preamp tube socket. I am not sure about an octal tube with a base though?? I saw a few amps on ebay like that too.

McIntosh is doing an anniversary amp with LEDs under the tubes.. Most people complain that you can't turn the LEDs off. I guess if it were me I'd like to be able to turn the LEDs off.

I think you can just drill a hole in the center pin of the KT88s and GZ34s to get the light up into the tube. Or angle the LED towards the tube at an angle from behind the tube.

Def. LEDs for the effect. Just some LEDS, a drill and some high temp silicone to hold in place. It could be a 12 volt walwart power to supply the LEDS or something.. Or some of the tube heater power.

Gimickey... I dun know. Could be cool to see up in person.

It is a cool affect - my c220 has LEDs that you can switch off and on - you need
to remove the cover to see them though - here is a shot I took with the cover off:

I've built quite a few preamps with either blue or violet LEDs under the tubes, here's a photo on one on my SP12 preamp
With an RGB LED you can have an infinite variety of colors and intensitys
On an octal tube, "very carefully" would be drilling a small hole (very carefully!) into the locator pin

how do you power the led's?

resistor and filament power

do you have a diagram including resister values?

the main question i have is: can you tap into the 6.3 volts on pins 2 and 7 of the outputs and pins 4 and 5 on the 6an8 or do you need a seperate filament transformer

same as powering any other LED, most LEDs need about 2v. The resistor value can be anything in a range that will give the LED around 3 to 10 ma of current, so with 6v filaments I'd try a 470 ohm resistor, with 12v filaments a 1K usually works very well, some blue LEDs are too bright, so a larger resistor. Take the voltage right off the tube filaments, can be either AC or DC, doesn't matter, an LED will work with either, but if it's DC then the polarity needs to be correct. LED is connected in series with resistor. It won't hurt to hook it up backwards, it just won't light up.