Tsl 122 Issue

[Rds]

Hey thanks for looking. My problem is my tsl intermittently sounds much louder and way more overdriven when I turn it on, then after a few minutes it will revert to the normal sound of the amp. Almost like a switch was switched. It sounds like way more power when this happens. I actually like the sound but it's not right. I did buy a new board and I'm thinking this will cure this. Current board I think is original. Amp was biased after new tubes 2 to 3 months ago. But had done it before that only once or twice. Told the tech but he found nothing. Wondering if anyone has encountered this.

 

[RickyLee]

Did your tech monitor the bias for an extended period of time, to check for any drifting bias issues?

Or have you performed that function/checked it yourself?

 

[Rds]

Thanks for the response. It was biased recently with new tubes and was doing this before and after. Have not checked biased since. I will be installing the latest board. I'm hoping and thinking it will fix the problem.

 

[RickyLee]

The other thing I am wondering is if the FX loop relay is acting up. On many TSL100/122 amps, the amp either loses or gains volume when the FX loop is engaged. But the loop only engages when a plug is inserted into the loop return? (I need to check that on the schematic later to see which plug or if both/either engages it).

But it might not be that issue anyway as you say it gets really loud AND distorted.

Does it do this on all three channels? Did you rule out the front panel switches (EQ, Deep) are not opening/closing?

 

[Rds]

I have cycled all the switched several times while it's doing this. I thought maybe vpr switch at first but works fine with no bearing. While acting up vpr does reduce volume/ power. Once or twice amp has also blasted out at same elevated volume a feedback sound even in clean. Strange. Doesn't do this every time I turn it on. Only sometimes. I guess the board could be doing something weird. Also have tried reverb on and off. May try unhooking it too. I appreciate your input Ricky. It's a great amp. My first tube Marshall. I will post when I get the board in soon. I'm not sure what board version I have. Very interested to see.

 

[RickyLee]

It sounds like a cold solder joint or connection somewhere inside.

So when it does it in Clean mode, how much more volume is it? Double? And did the overall tone remain the same when it did it on the Clean channel? As in, did it still sound like the Clean channel but with just more volume?

I was wondering if the connection to your NFB loop is acting up.

But to verify. Are you certain that the loudness is the problem? As in, could it be that when it goes loud that is where the amp should be normally and the problem is making the amp lose volume?

 

[EADGBE]

It could be anything. Do you have a good amp repairer you could take it to? Because what if you changed the board and the problem didn't go away?

 

[RickyLee]

The year of the amp is within the serial number on that white tag on the back chassis panel.

 

[Rds]

Hey Ricky. I changed my board and biased my amp. So far no problems. It's clear the old board had issues. The volume is consistent and correct. Sounds good with balls. The old board was one of the jcm2-60-00's. The preamp socket solder joints had some funny corrosion. Maybe a questionable joint. old board ran hot as hell. The new one runs much cooler. I biased it at 88.5 both sides. Board Chang was a good move. Thanks for you input. Plenty of other things in there to go bad.

 

[ntrueman]

The PCB breaks down on those old boards and they are fitted with incorrect resistor values which cause bias instability (which can cause tube cooking). I changed mine and everything was fine afterwards. If someone is looking to buy one they can be found here: https://www.tubesandmore.com/products/pcb-marshall-valve-pcb-tsl100tsl122. It is possible to fix the old board but it's a lot of work which is probably not worth it due to the number of hours it will take.