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Author Topic: SUNN 300T one green LED turns red  (Read 363 times)

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SUNN 300T one green LED turns red
« on: November 23, 2017, 05:45:03 pm »

Hallo !    This is my first post here and my problem is a MYSTERY !!    The amp has one bicolour LED  ( green /red)  for each pair of the six powertubes .  At start all three LEDS  glow red . After stand by on all turns green .....  but after 3-4 minutes one of them  (  for V9+V10)  turns back to red.   The green part of each "doubleLED"  is driven by a 2N4401  transistor .  All three transistors are OK.
Resistorchain 220k+220k + 4,7k to ground are OK.   At first all green LEDs show about 2,2 VDC at its anode ,  but after 3-4 minutes this anodevoltage slowly starts to raise up to about 3,6 VDC
and the red lights up .   The 4,7 k resistor has its upper end to the base of the transistor.   Please look at the schematic .   The only thing I can imagine is that the internal resistance in the green
LED is increasing and in a way therefore is chooking the transistor .....  That in turn increases the voltage to the gred side which turns on .      I´d be very happy for some advice here .....
I´m very  puzzled  .   The usual fault which shall turn the LED back to red is the connected fuse of 100mA to break or that the high voltage to the actual tubepair have gone away.....  or some
fault with the tubes involved .   A broken fuse here will disconnect the actual pair of tubes and the amp can still work with four outputtubes .......  In my case here nothing is wrong with the tubes
I just want all the "doubleLEDs to work properly.                                 Thanks for all comments                   Regards  Stewen


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Re: SUNN 300T one green LED turns red
« Reply #1 on: November 29, 2017, 07:02:12 am »

Hi Stewen,

did you try swapping the corresponding tube with the one next to it?
If the other LED changes color now, then the tube is the problem.
If it's still the same LED, then the fault is in the circuit.

Cheers, Peter