LED Replacement Lights

Does anyone have a contact for purchasing a replacement LED strip in my Tubemeister 18?

Hi Dmccorkle.

That's an odd one, what has gone wrong with it? Is it damaged in some way or are you just trying to replace it with something different? For a part for part replacement it may be that the only people you can turn to are H&K themselves and they usually will not supply parts to private individuals, only to recognised repair outlets.

They are just super dim and I feel like they are going out.

Ok.  If they are dimming as a general thing, I mean all going down by the same level as a block, then you have some sort of problem in the LED PCB power feed and that might be a very simple fix.  The LED PCB is fed by two thin wires to the right of the front panel as you look at the amp from the front.  If you have had the top off for some reason, such as doing a valve change, it is possible you have nipped that or even damaged a connection on the end of the PCB when you refitted.  It's a simple matter to remove the lid again and check that out.  Would you be confident in doing that yourself, it isn't a very difficult or dangerous job?

The correct procedure is:  Remove the top two screws and the rear middle on each end cap fully.  Leave the front middle alone, it only holds the handle onto the end cap.  Unscrew the two lower screws by only a few turns to loosen them and let them flop outwards enough to lift off the top.  You can power the amp up like this as long as you keep your hands out of the way.  Check out the LED PCB for nicks in the tracks, there are only two of them.  Have a look at the cable solder joints on the end.  Also you could power up and check out each of the 4 LEDs on the board by pressing it gently, one of them may have a broken joint.  If the LEDs jump back to full brightness you have found the problem.

If you have had any other work done in the bottom cavity of the amp it is also possible that the problem has been caused there.  The LED power feed socket sits on the main PCB directly behind the input jack socket.  It then feeds through the chassis and up to the edge of the front panel.  Here is a picture of your interior from underneath:  TM18 Interior.  You can see the LED power feed socket in the lower left corner.  It's the white one with red and black wires coming from it.  I wouldn't suggest you open the bottom cavity, if that needs checked out then it might be best to take it to a professional.  Taking the lid off to look inside the valve cavity is perfectly safe as long as you are just sensible.  There is no voltage in there only hot valves to avoid touching.

If you think you are capable then I would check out the top section first then think of getting someone more qualified to investigate the bottom.  There is no guarantee that changing out the LED PCB is going to fix your problem and it may not even be necessary.


EDIT: Just had another thought. The PCB is held down on the Perspex front panel with 4 metal clips. Have you had to remove them and refit the PCB at some time? Did you fit the PCB the right way up? The tiny surface mount LEDs must face downwards of course. And if the clips are somehow touching the PCB tracks then they will pull the levels down and even fully off.

I have taken it apart and verified the connection. With it apart I powered the unit up and the strip is just very dim. I have since ordered a 12-inch blu led strip with an external power supply because it needed 24 volts so we shall see.

Ok, I hope the new setup is what you need.

The power in the TM18 to the LED PCB is from a -22V source through a 680R resistor to set the LED current on the main PCB.  If all of the LEDs are dropping in light level equally then it leans towards there being no problem with an actual individual LED component.  It is still possible that one of those LEDs has cracked a joint which would affect all of them in exactly the same way as they are in series and share the same current.  In fact any problem in the voltage feed line would affect them all equally for the same reason.

Let us know how you get on with the new setup, it may help someone else in the future.

Thank you. I will update once I get it all resolved.