Trace Elliot SMX GP12 Valve blend not working

[mathieu]

Hello! I just got a Trace Elliot head second hand and when first plugging it in, everything seem to work fine (it goes loud and then some, built-in compressor is great etc.). However, I discovered quickly that the solid state to valve blend doesn't seem to work. When all the way to solid state the sound is loud and when turning towards valve it gets progressively quieter until there's no sound at all when it's all the way to valve.

 

I tried swapping out the tube with a known working tube but that changed nothing. I got it for a fairly good deal and the cost of repair quoted by a pro (£100) would be more than the cost of acquisition. It may still be worth it, but I wanted to check my option first... Is there a way for me to diagnostic the issue and see if it's worth fixing?

 

In addition, when I use pedals in between the bass and the amp, there's a loud pop when the effect is turned on or off. That doesn't happen with my other amp.

I found the repair manual online so I have the full schematic which is cool. I've got a multimeter and some basic tools and I'm willing to learn (if it's not too dangerous of course).

 

 

Edited February 10 by mathieu

[Bassman72]

Watching this thread with interest as I have a similar issue. Power tests by the technician were all good yet I get no overload trigger on the pre-amp no matter how hard i push the input. 

 

Incidentally, can you please post the link for the schematics. Thanks! 

[Bigguy2017]

Remove the valve and check the voltages on the valve socket - carefully... You're looking for +15 VDC on 6+8 (heaters) and +40  to +150 VDC (HT) on pin 4.

 

You have tried another (known good?) valve...

 

If voltages are there, clean and tighten the valve socket contacts (obvs. with power off and drained!) and have a good look for a cracked PCB trace around the valve socket.

 

Measure the values of R2, R12, R13 and C6 - anything open circuit?

[mathieu]

12 hours ago, Bassman72 said:

Incidentally, can you please post the link for the schematics. Thanks! 

 

Here's a link: https://www.manualslib.com/manual/1084717/Trace-Elliot-Gp12-Smx-Series.html#manual

It's amazing how detailed it is!

 

11 minutes ago, Bigguy2017 said:

Remove the valve and check the voltages on the valve socket - carefully... You're looking for +15 VDC on 6+8 (heaters) and +40  to +150 VDC (HT) on pin 4.

 

You have tried another (known good?) valve...

 

If voltages are there, clean and tighten the valve socket contacts (obvs. with power off and drained!) and have a good look for a cracked PCB trace around the valve socket.

 

Measure the values of R2, R12, R13 and C6 - anything open circuit?

 

These are the measurements for each pin:

Pin 1: 0
Pin 2: 0
Pin 3: 0
Pin 4: 2.29
Pin 5: 14.73
Pin 6: -0.77
Pin 7: -0.64
Pin 8: 0
Pin 9: 8.43
 

I've measured R20, and get ~170 on one side and between -0.5 and 1 on the other side (there's a glob of glue on that side so the measurement may be inaccurate but I tried my best!). 

 

I can try measuring what you suggested though!

[Bassman72]

4 minutes ago, mathieu said:

 

Here's a link: https://www.manualslib.com/manual/1084717/Trace-Elliot-Gp12-Smx-Series.html#manual

It's amazing how detailed it is!

 

 

These are the measurements for each pin:

Pin 1: 0
Pin 2: 0
Pin 3: 0
Pin 4: 2.29
Pin 5: 14.73
Pin 6: -0.77
Pin 7: -0.64
Pin 8: 0
Pin 9: 8.43
 

I've measured R20, and get ~170 on one side and between -0.5 and 1 on the other side (there's a glob of glue on that side so the measurement may be inaccurate but I tried my best!). 

 

I can try measuring what you suggested though!

Many thanks for that!