Simple question I hope

[Oldmactech]

Thanks, the last two post remind me how over my head a lot of this discussion is.
So, see if I understand? With no tubes installed likely my LED won’t survive initial turn on?

[Tom Phillips]

If I were replacing the LED I would do the following if I already had the unit open.
Install a replacement R51 using a value that limited the LED current to a safe value under worse case conditions. I.e. with no tubes installed. Hopefully, the LED brightness would still be sufficient under the lower actual operating conditions with the tubes installed.
Note that all LEDs are not the same brightness. You can buy a high brightness LED if you determine that you need to replace the one you currently have.

I know all this is a lot of work. Best to think of it as mostly a learning experience rather than a giant pain in the ass job just to replace an LED.

Cheers,
Tom

[Helmholtz]

With R51 upped to 2.2k the LED current will be 20mA with a no-load voltage of 47V. So no problem here.

But because of the low reverse voltage of 5V, reverse connecting the LED is likely to kill it (leaving it shorted).

[Tom Phillips]

With R51 upped to 2.2k the LED current will be 20mA with a no-load voltage of 47V. So no problem here. But because of the low reverse voltage of 5V, reverse connecting the LED is likely to kill it (leaving it shorted).

Per post #41, Oldmactech measured no voltage drop across R51 so something seems to be open circuit rather than shorted. That is, unless the description in post #41 is incorrect.

[Oldmactech]

Reversed the polarity of the LED, lit right up. Begin putting it all back together, see how long it last.
Thanks to all for the guidance. This has been a great learning experience and if it fails again I’ll know what to do. Part of my frustration is I don’t have a good supply of small parts (resistors, diodes and such) so I’m constantly stopping and starting to shop for stuff. I guess that was what Radio Shsck was good for.

Thanks again.

John

[The Dude]

Reversed the polarity of the LED, lit right up.......

This is not an "I told you so" or me trying to be a "Richard Noggin", but precisely why I recommended using your meter instead of going by LED legs and circuit board symbols. It's easier to take a couple minutes with a DVM than it is to have to disassemble the amp a second time.