Marshall Tsl 100h Problem

[Sarah BAT]

Hi guys!

Found a link to here on the marshall forums, hoping someone can help me out!

So a few days ago my marshall tsl died after playing it for ~20mins at low vol. The whole thing just shut down, lights valves everything. Checked the Mains Fuse and it was blown. So i changed that out and its working now.

So obviously the fuse blew for a reason. So i took out the valves and gave them an eyeball and it doesnt seem that they are blown. and in fact the amp sounds grand when i play thru it.
So, i figure it must be the bias. (they amp has been in storage for ~18months) So i start on the left side. was slightly low at 78. i crank it up to 82. start on the Right side. at first i got something stupid like 11, so i cranked it up and could only manage to get it to 15. I re checked the left, which had gone off slightly.
Now i try to adjust the bias on the right side, and i can only seem to get a reading of 0.8! the right tubes look to be glowing hotter than the left side, but i cant tell how much juice is getting to them!

I have a gig on saturday that i need the amp for and there is not a tech near me than i can bring it to!

Ide really appreciate some help, as im totally stumped on this one and google isnt really being too helpful!

Thanks a million

Sarah

[oc disorder]

Hi Sarah Bat
Welcome to the forum.
Firstly it does strike me that there maybe something wrong with some of the tubes maybe one.
Could be an intermittent fault in one of the tubes.
Also could be some problem with the circuitry on one side.
Have to do some detective work with the resources you have available.
Number the tubes 1 to 4 on the base witha felt pen or even a scratch on the base.
Swap the left 2 for the right 2.
Does the low reading go from the right to the left now ie follow the possibly suspect pair ?
I'de keep it around 70 at the moment 35 per tube is fine.
If the problem moved with the tube swap now we can use the amp as a primitive tube tester.
In one side plug in the tubes individually and take the measurements.
In a perfect world they should all be drawing the same.
If it was set to 70 with 2 the reading with one should be half that.
So they all should measure approx 35.
My guess is one has an internal short and probably wont read much at all.
If the problem stayed on the one side there must be a problem with the circuit , maybe even the 1 ohm resistor on the cathode which you are measuring across. Doubt the output transformer has a fault as you said the amp sounded great when you played through it.
My personal experience with them has led me to think that the 90mA current is abit too high and leads to premature tube failure.
Hope this is some help ..I would order a spare set of output tubes just in case !

[Sarah BAT]

Thanks OC, and thanks for replying!

Since posting this thread yesterday i used my amp last night for practise. I turned the bias down to ~40 on the left side, and as i cant get a measure from the left side i carefully monitored the Valves to make sure they were glowing even. Which they were. and there were no Crackles, or pops or no dropouts what so ever. There was a sacrifice in the tone and volume alright. But when i cranked it up full blast without the Dampener switch on, it sounded reasonable!

This is not the ideal situation i know, but i cant get it to a tech before the weekend, and i really need the amp for the weekend!

I will Test the Valves by switching them around to see if its the valves or a problem with the circuits!

Thanks for replying

[Enzo]

YOu can also do this. Pull all four power tubes. Number them like oc suggested.

Plug just one tube into the end socket. Power on. Adjust bias for one tube if you usually want 80ma, then set the single tube for 40ma.


REmember that the left bias control and the left test point pin are for the tubes on the right, and vice versa. I don't know why either.

If that tube biases up OK, pull it and try the next tube in the same hole. Test each of the four tubes in the same socket all alone. if any tubes come up lame, then probably bad.

Now take a good tube from the batch and stick it in the second socket. see if you can bias it there. Now the third and then fourth sockets. Remember the last two sockets use the other bias adjust control and other test pin.

We just tested each tube and each socket. If either a tube or a socket has a problem, it should have shown.

Your fuse blew for a reason, probably a failed or failing tube. The faikling tube could have damaged the amp by burning up a screen resistor or the 1 ohm sensing resistor.