AFD100 - Lost all gain only clean sound

[Dude456]

Hello,

I’ve recently got an AFD100 for a great price, it was basically sitting in its box for a long time, so it’s still got the original Marshall tubes in it.

Today, I had some free time and decided to crank it, it was glorious for like 10 minutes, and then it just suddenly cleaned up, without making any popping or weird noise.

I have turned it off, waited 10 minutes and turned on with the auto-bias, it went through without showing any tube failure. I have tried three different bias settings, but the amp only outputs a very low volume clean sound now, no matter which mode I use (AFD/#34).

Another thing I’ve noticed, is that some of preamp tubes are glowing like a lightbulb and the 6550 tubes are glowing more than I’ve seen before. I don’t have any spare tubes at the moment, but I’ve ordered a kit, let’s hope that only the tubes are bad. However, it is strange that the internal tube failure check doesn’t show any problems.

The Power attenuation was on 10, so basically it was turned “off”. The Gain was on 10 (#34 mode) and Master was around 8 when this happened.

Should I be worried, or just the tubes went bad?

Update: I’ve checked the tubes with a chopstick, and 3 out of 5 preamp tubes are super microphonic, and V3 was crackling when I tapped it.

Thanks for the help in advance!

 

[dtier]

Hello,

I’ve recently got an AFD100 for a great price, it was basically sitting in its box for a long time, so it’s still got the original Marshall tubes in it.

Today, I had some free time and decided to crank it, it was glorious for like 10 minutes, and then it just suddenly cleaned up, without making any popping or weird noise.

I have turned it off, waited 10 minutes and turned on with the auto-bias, it went through without showing any tube failure. I have tried three different bias settings, but the amp only outputs a very low volume clean sound now, no matter which mode I use (AFD/#34).

Another thing I’ve noticed, is that some of preamp tubes are glowing like a lightbulb and the 6550 tubes are glowing more than I’ve seen before. I don’t have any spare tubes at the moment, but I’ve ordered a kit, let’s hope that only the tubes are bad. However, it is strange that the internal tube failure check doesn’t show any problems.

The Power attenuation was on 10, so basically it was turned “off”. The Gain was on 10 (#34 mode) and Master was around 8 when this happened.

Should I be worried, or just the tubes went bad?

Update: I’ve checked the tubes with a chopstick, and 3 out of 5 preamp tubes are super microphonic, and V3 was crackling when I tapped it.

Thanks for the help in advance!

Hopefully just a bad pre-amp tube but not sure about what your seeing. Can you post a pic of the tubes powered up?

 

[LyseFar]

Check HT fuse

 

[Dude456]

Check HT fuse

I have checked it, and even tested with a different one, but it doesn’t seem to be the fuse.

Hopefully just a bad pre-amp tube but not sure about what your seeing. Can you post a pic of the tubes powered up?

I’m out of town right now, I will post some photos of the tubes when I’m back home.

 

[Dude456]

TL;DR: It wasn’t the tubes, but I suspect a bad/cold solder joint somewhere on the input board. Long story below.

The preamp tubes have arrived, I’m still waiting for the 6550 quads.

Removed the old Marshall branded tubes, cleaned the tube sockets using the Deoxit Survival kit and inserted the new TAD preamp tubes, (I have also cleaned the power tube’s sockets, just to be safe). Turned it on, let it sit for 2 minutes in standby, then I have turned it off to activate the auto-bias.

After it finished, I turned off from standby and slowly turned up the master and gain, but it still not had any distortion. I have tried to tap the preamp tubes with a chopstick, and none of the new ones are microphonic.

I have tried to plug in my guitar to the FX return, it gave me a loud signal, so the power tubes should be good.

Then when re-plugged my jack into input 1, it almost blew my head off with that glorious Marshall tube distortion! Started playing happily, but the distortion started to cut in and out. Whenever I plugged it out and jammed the cable back in, it would roar for a few seconds. Interestingly, if I wiggled the cable while it was plugged in, it wouldn’t do anything, it only worked when it was unplugged and plugged back in with some force (same with Input 2).

Based upon this, I think there might be a bad/cold solder joint somewhere on the input board.

Edit: Forgot to mention, I have tried the good ol’ patch cable in the FX loop, but it didn’t make any difference.


Anyway, here are some pictures of the tubes, after they have warmed up

 

[maico996]

Try spraying some Deoxit on a large pipe cleaner and run that through all of the jacks - input, fx loop, speaker outs. I had a similar issue with a JCM 800 although not as bad as what you’re describing. Cleaning the jacks solved it.