HT-1 Combo - No Sound (Speaker/Headphones)

[Mr-T-Moe]

Hello,

my HT-1 Combo just isn't working anymore.

It was working just fine, after a few month I turned it on again and it just isn't working.

The red light is on, the Speaker and Headphones both are not working with an instrument.
I tried different guitar cables and guitars. Not working.
The only thing that is working is the MP3 input, there comes some very bad noisy and popping and quite quiet sound of the speaker.

I read that in some cases one of the valves blew the fuse. I checked and the fuse is okay. I don't know on how to check the tubes, they look just fine, no burning marks or cracks.

Any hints what might be the problem?

[thephantum]

Looking at a tube will tell you nothing about it's condition. A tube can be completely shot yet look and glow totally normal. All that means is that the heaters are working. The only way to tell is to either put the tube in a tester or swap it out for a known good one.

The fact that you have power meant the mains fuse (on the back of the amp) was fine. If a fuse is blown, it's the HT fuse on the PCB. If that fuse is blown, the amp needs to get checked out. Fuses blow to protect downstream components from extreme voltage and current levels. So if the fuse blew, something is wrong.

Having said that, if I had to guess, it's a bad power tube. The good news is that the HT1 does not require biasing. So you can put a new tube in and check/replace the HT fuse (if necessary). If the amp comes back to life, you're done. If not, it needs to go to a tech.

[Mr-T-Moe]

Thank you for your tips, but they did not work.

I let both tubes swap with brand new JJs.
As I said, both fuses are all right, the PCB and the power fuse.

Still the same problem. The amp is nor working for the guitar. Only the MP3 input gives a miserable and quiet sound to the output.

The tech said it might be one of the many operational amplifiers. The HT1 is not even a pure tube amp he said, it is full of these operational amplifiers and thus must be considered hybrid. If it would be a tube amp only he would be able to repair it but these micro electronics are not that easy to replace.
Did anyone experience problems with these operational amplifiers or the PCB board? Besides broken tubes and fuses?

According to my problem description (guitar input doesn't do anything, MP3 input is some kind of working but cracking and quiet) which of these operational amplifiers might be the problem? There are at least 7 of them.

Is there any possibility to get a complete new HT1-PCB board from Blackstar? Without the tubes and transformers?

[thephantum]

I think the only way to get a PCB is to be an authorized service center.

I agree that the HT-1 could be called a hybrid...but so could lots of other modern amps. An amp can have an "all tube" designation, but have a solid state PI. To some, that's still considered hybrid. The fact is that while there are opamps helping shape the sound, the power amplification stage is an all tube design.

I also disagree with your techs assessment. There are lots of pieces of pro equipment that are purely opamp driven and they can be repaired. So why can't a "hybrid" amp that has opamp components?

To my knowledge, the HT-1 has been pretty rock solid, so while it's possible an opamp is the problem...I highly doubt it. I would start by checking things like grid resistors or even rectifier components. I had a Marshall years ago that had the same symptoms (minus the MP3 part of course) and it turned out to be a bad filter cap in the rectifier for the low voltage rails...