What kind of a tube issue does this sound like?

[Michael Mueller]

Hi - I’ve had my DSL 40CR since 2019 and I’ve given it quite a bit of use but only at lower volumes in my basement. Over the past month or so I noticed an inconsistent hum/status where one day it is on any channel that I switch to, and the next day it’s gone. I have always had the amp used on the 20 Watt setting on the front of the amp, and the other day i turned it to 40 by mistake and noticed it is anything but silent on that setting. I hear a hum or “wind” type sound that is there until it goes to standby or the 20 watt setting, where again, there may be a sound there.

I talked to an amp repair shop over the phone and they said it sounds like the pre-amps. I’ve never swapped tubes out before. I ordered a replacement set of 4 pre-amps (same as stock) and it seems like I can put them in myself.

Considering the sound coming on when I turn it to the 40 setting, does that also imply something with the power tubes? I’m not sure if I mentioned that part to the amp shop. And if so, can I swap those out myself too or do I need to find a place to bias it (whatever that is!) as I see written? The amp has basically just sat in the same spot in my basement for 3 years without being moved around if that matters.

Thanks,
Mike

 

[Chris-in-LA]

Try using one of the new preamp tubes to replace one of the old preamp tubes. If that doesn’t work, put the old one back in and try swapping the next one with the new tube and so on. You probably don’t have all bad preamp tubes. Let us know if that fixes it.

 

[StingRay85]

"I talked to an amp repair shop over the phone and they said it sounds like the pre-amps"

LOL

Preamp tubes are just one of the usual suspects... It can be 10 different things. A repair shop that gives you advice by the phone, very strange

 

[Michael Mueller]

I did the tap the tubes lightly with a chop stick test and on the first power tube it looked and sounded like the 4th of July.

I guess it’s time to change everything out.

 

[KraftyBob]

Plug your guitar into the effects return and see if the sound goes away. If it does, that indicates the problem is in the preamp section since that is bypassed when doing this test. Then as Chris-in-LA suggests, swap one preamp tube at a time to see if it's a tube and which one it is. It makes sense it's louder on the 40w setting as the plate voltage increases when that's selected. At that point it's just passing the signal it receives from the preamp and amplifying even more.

The only thing you need to worry about when replacing preamp tubes is to make sure the pins are lined up correctly. There's a gap between pins 1 & 9 that matches the same gap in the tube socket. You don't have to bias preamp tubes - just plug them in.