TSL601 - No Sound

[Stevo6791]

Hi

I have a TSL601 which I’ve had for at least 17 years, It’s been running fine until yesterday when I got crackling on the speaker while playing, it seems to go and I continued my playing session.

Today, I’ve turned on the amp and there is no sound at all on any of the channels.

What I know

-User replaceable Fuses are all ok
-Standby light is on
-All Tubes are lit
-When I switch the standby button there is the same slight crackling in the speaker I heard yesterday, But only every now and again.
-On the lead channel with no instrument plugged in I get a high pitched squeal. With instrument plugged in this doesn’t happen, other 2 channels are silent apart from random crackle.
-the fx return is also silent.

Valves have been in the amp since around 2006ish they are J/J E34L power valves, original Marshall pre-amp valve.....this amp is only very occasionally used. In the 17 years I’ve had it I say it’s had about 4 years of playing, used quite a lot when I got it no so much these days.

I have opened the amp just to have a quick look to see if there was anything obvious, there are two samwha 315v 330uf caps that appear to have domed tops but I’m not sure if this is just the plastic Coating on top Of the cap, if I push on it it returns flat. There was nothing obvious, no smells.

Would like to know if anyone here could narrow this problem down from their experience before I decide where to spend pennies......I’m hoping it be valves. I have had this amp die before not long after I got it which is why it has the JJ valves in but that was just dead, this time its still alive but has no output.

Thanks

Steve

Ps, I have basic multimeter skills so don’t go to tech on me...

[The Dude]

Try jumpering the effects send to return and see if it works. You could just have a switching jack issue.

[glebert]

Try jumpering the effects send to return and see if it works. You could just have a switching jack issue.

I'm pretty sure these have parallel effects loop (if it is like my TSL head). My amp also has no sound (I got it as a fixer project). The problem with mine seems to be the output transformer having an internal short. I put it on my variac with a light bulb limiter and the bulb glows and can get almost no voltage across the primary side. I don't know if it would show up on a multimeter test. I also don't know if that is the only problem mine has or not, we'll see when the transformer gets here.

Good luck.

edit: check the speaker impedance selection switch. If that is really dirty it could cause a problem like you describe. I had a Carvin X100b that acted that way because of a stereo cabinet that had a bad switch. You can test the switch resistance by plugging a cord into the output jack and measuring the resistance from tip to sleeve. You will be reading the combination of the switch and the output tranfomer secondary, which is usually pretty low resistance (less than 10 ohms? I think?). Measure it in both positions and see if it varies as you switch it a few times.

[Enzo]

Then plug into the FX return with the guitar. That tests the power amp.

[Stevo6791]

Hi

Thank you for your suggestions, I went to try said suggestions only to find the amp has come to life again. Yesterday I took all the tubes out and opened the amp to see if there was anything obvious. When I closed it up, I put the Tubes back in just randomly but never turned it back on until just now, so perhaps that did something?

It is really muddy Sounding though. Sounds like the amp is wrapped in a duvet. I think I’ll just buy a set of new tubes see if that helps?

My only other thought is maybe a dry joint? when it’s heating up something is disconnecting inside? But it’s been on for 30 minutes and it’s still on. Yesterday (before the tube removal) There was nothing but crackle and that high pitch sound on channel 3.

Oh almost forgot, I did notice in one of the E34L’s that there’s little while flakes Inside the tube. Only in one not the other, Is that normal?



Thanks, I’ll try the new tubes and see what happens.

Steve

[Enzo]

Flakes are not a good sign. Kinda like finding flecks of metal in the oil in your car.

[Stevo6791]

Hi

Yes I read that earlier, apparently sign of a leak? There was also very fine flakes in the other tube, really small like dust. The other one had big flakes in it.

Anyway I got two new matched tubes, I checked the bias before removing the old tubes (the amp was still alive today?) and they where 39.8mv (left pin and center) 39.8mv right pin and center). I’ve never checked those before so assume it’s correct? The TSL 601 apparently needs to read 80mv so I assume this would be 40mv left pin/center and 40mv/center right pin equaling 80mv for both? So before I put the new tubes in is that a correct assumption, would that be somewhere near?

I understand there can be more to it to bias Tubes properly but i certainly don’t feel comfortable checking voltages etc inside the amp, so the three prongs and the pot is what I have to get it somewhere close. It’s only a house amp and is not driven very hard or for very long.

Thanks for any advice

Steve

[Enzo]

Three bias test point pins: the middle one is ground, the two end ones are wired together.

[g1]

The TSL bias chart does say 80mV, perhaps someone set it to half, not knowing it was for the pair rather than for a single power tube.
Or one of the tubes could be dead. Try pulling one power tube and check at the test point. Then check the other by itself. If they are both working, they will probably measure around 20mV each.
Aside from the power tube/bias issue, I think the 'no sound' condition is a separate fault. You should still get some kind of sound with one power tube running.

[Stevo6791]

So does that mean this amp has been set at half the bias it should have been all these years? Not that I know what that actually means Those power tube where put in around 2006. It was done in a local music store, it’s never been touched since.

So just to clarify, left pin and center should be 80mv, and the right pin and center should also be 80mv, just want to make sure that is absolutely correct so I don’t damage anything.

Steve

[g1]

Yes that is correct if they are both working.
What I was getting at was that one may not be working, and you are measuring 40mV there due to only one working.
So check them one at a time first, then after confirming they are both working, you can dial it up to 80mV there with both installed.
If only one is working right, and you dial it up to 80mV, it will be bad for that tube.

[Enzo]

Left and right pins are wired together inside. SO measuring both left to ground and right to ground is just taking the same measurement twice.

If the amp has been at "half bias" all these years and no one cried foul, it just goes to show how completely UNcritical bias really is.

[alexradium]

All the 2000 series amps have heating problems on the bridge rectifier for the preamp tubes filaments,it is mounted with no clearance from the board,the heating causes soldering cracks.

[Enzo]

My take on that: it is a multiamp bridge for a current load of less than an amp. What I find in most cases is the solder never wetted to the bridge legs when it was made. I remove the bridge, clean the legs with either an Xacto blade or a Dremel, and reinstall it. I never had one come back. The legs on the part had tarnished before installation.

[Stevo6791]

Yes that is correct if they are both working.
What I was getting at was that one may not be working, and you are measuring 40mV there due to only one working.
So check them one at a time first, then after confirming they are both working, you can dial it up to 80mV there with both installed.
If only one is working right, and you dial it up to 80mV, it will be bad for that tube.

I tested both old tubes one at a time and they both tested around 18.8 that was only with a few minutes of warm up, so like you say they are probably around 20mv. So they are still working. Will the lower bias affect the sound?? I’ve never been quite happy with the sound of this amp and bought pedals to compensate. So knowing both tubes are working but under biased, Do you think it’s safe to try in the new tubes and bias them to 80mv?

In regard to the other issue, the loss of sound completely, could it be a dry solder joint? It’s only ever happened that one time. The only thing I did between it not working and coming back to life was remove the tubes and chassis, then put it back together, I didn’t nothing else. Could it be possible there is a dry joint on one of the tube sockets that when I’ve removed and replaced them it’s reconnected something? Or is that unlikely.

Thanks all for this advice

Steve