Tubemeister 18 Red box works but nothing comes out from the speaker

Hi, just recently bought a Tubemeister 18 head, secondhand. As a first thing I replaced the power tubes so they are brand new. The amp works fine through red box fine but when I plug the amp to the speaker, nothing comes out. I have a Tubemeister 5 combo which speaker I'm trying to use now (I have 112 cabinet as well in the band room to test later.) Any idea where the problem could be?

Thanks!

Hi Buddyolli, (you're not a Brit cockney by any chance? )

If the Redbox is working fine then there is signal coming out of the power amp and output transformer as the Redbox shaping circuitry is fed its input direct from the output transformer terminals.  The problem would seem to be in the Power Soak section, that area links in with the TSC and protection circuitry too, or the connections and cabling to the speaker.  Things to check...

Check the Power Soak selection switch is not set to Silent, (the speaker with the cross through it).  (Yes, we have all done it so it really is worth ruling out.)

If it is not on silent, is it not working for all settings, 1W 5W 18W?

Is the cable known good?  Try it with a different speaker cable just to rule that out.

Are the connections between your TM18, speaker cable and the speaker right up to the driver terminals actually secure?

Have a look at the two red TSC lights on the back.  What do they show, are they on or off, one or both?

Let us know this info and we can go from there.

Hi and thanks for the reply!

I have been playing with these Tubemeister series amps now for around 10 years. I used to have this 18 head earlier but I sold it, and regretted immediately. So, now got it back... I have also the big brother, head 36.

I have done the following:

- I bought a brand new speaker cable since I did not have any free ones.
- I have tried all the power soak options (silent/1/5/18), and red box works with all. The latter 3 have all the same problem that nothing comes out from the speaker.
- The red lights are both off when the amp is in the play mode, so all should be fine. The lights are then also on in the standby mode as they should be.

In any case, I will try the amp with my 112 cabinets during the weekend, and see if there is now something with the 5 combo speaker and 18 head combination (even they should be compatible). The 5 combo works fine with the combo amp itself. It should be possible to use external amps since it has the plug.


Thanks!

You're welcome.  Apologies if I seemed to "teach my granny to suck eggs", I had no idea whether you were an experienced user, (which you are), or a total beginner.  Even with your experience it is sometimes useful to go into more detail than you need as others may come across this who aren't as knowledgeable as yourself and it would help them too.

So, speaker cable is ruled out, that's good.  Stick to the new one for testing where you can.  Next, it is just possible that the output socket may be the problem.  As an experienced user you will know how to clean that.  It would help to rule that out as a possible issue.

The Redbox working definitely points to the fault being after the output transformer so inside the PS/Speaker Out section.  This is viewable through the bottom of the amp.  You have ruled out the possibility of an open circuit component in the power soak.  Any single component is specific to only a single setting or two, there is none which affects all three active settings.  The fault is there with all settings including 18W, and 18W is straight through with no components in the signal path at all therefore no faulty component is breaking the path on that setting.

Knowing that you know your onions, the next step is simple.  Have a look inside the base, through the ventilation slots, and you should see the PS components.  In the TM18 there are 8 of them, 6 large rough coated resistors and 2 inductors which look like slightly smaller shiny resistors.  The main resistors are large and grey while the inductors are a little smaller and more light blue.  They are all mounted in cut-outs on the edge of the output PCB.  Do any of them look scorched or damaged at all?  I have attached a quick pic of the PCB, and one of the layout with the relevant components marked on it.  While the components are not the problem, if they look badly scorched it may show that the PCB tracks have been stressed too.  Most heated components will discolour with time, you can see that with the inductors in the picture, a little darkening is not a problem but any signs of burning or flaking could be an issue.

If they do look a little scorched then how do the PCB tracks you can see look?

This really looks like it comes down to:  Faulty PCB, (burned or broken master track between transformer terminals and speaker socket.);  Faulty PS selector switch;  Faulty Speaker Socket;  Something external to the amp in the speaker line is faulty.

Thanks bordonbert,

fortunately the problem is coming from the incompatibility of Tubemeister 18 head with the 5 combo's speaker. The 18 amp is working like a charm with the 112 box, so problem solved. The TAD tubes are as good as expected.

There is the speaker plug in the 5 combo with a text 8-16Ohms above the plug, as with the other H&K cabinets. I should probably open the combo and see what's inside, or dig out more tech specs online. However, I think I will sell it, and just buy another 112 for my 18 head.

Thanks for your help!

You're welcome for the help, that is why we are here. That incompatibility between TM18 and TM5 does seem an oddity to me. That shouldn't be a problem. What on Earth can there be inside the speaker cabinet which would cause the amp to drop into Silent mode like that? Anyway, the problem is solved, good work.

Your description of the 5 Combo setup is a bit odd Buddy. When you mentioned the "Speaker 8-16ohm" text you must have meant above the speaker socket. I hope you have not been running the speaker cable from the TM18 head into that socket have you? If you have, that is totally wrong. That socket feeds direct to the TM5 amp's output stage not to the speaker at all. The speaker would be connected to the plug you have to pull out. You need to connect that plug to the TM18 with an extension type cable, not put the standard speaker cable into the TM18 head and the TM5 combo socket.