What did I just do to my amp that made it die?

Rick Lee

Member
Messages
11,381
I wanted to check the bias on my '69 Plexi clone build, as it's been hot enough to fry an egg on at band practice. I have the Euro Tubes bias probe. I've done new power tubes and bias on my SLO with smashing success. I don't think I did anything differently this time, but when I turned standby off, I got a pop and a flash. All tubes still glow, both fuses look fine, but no sound and zero on my readings. WTF did I do?

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Tone_Terrific

Silver Supporting Member
Messages
38,110
If the key is broken on the tube base and/or you insert it wrong the tube will respond accordingly.:eek:
 

Rick Lee

Member
Messages
11,381
Keys are fine. I checked the fuses again and this is what the HT one looked like when I pulled it all the way out of the holder. Ouch.

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I have some spares, so I installed a new one and got a BANG as soon as I turned standby off. I did this with the bias probe removed and otherwise haven't touched anything on the head. It was fine yesterday. WTF is going on?
 

metal_murf

Member
Messages
480
Follow the sequence on the directions. I don't have mine handy but when you hit the standby off in the wrong order it can cause a fuse to blow in the amp and/or your meter.
 

ZosoRush

Member
Messages
722
This is irrelevant but what cab are you using? I have the Purple Vintage Modern and i have been trying to figure out which color 2x12 would go best with it. Black is my last resort but was thinking about doing white tolex/black grill cloth
 

pfrischmann

Member
Messages
3,459
Pull the tubes and check your voltages. Something is out of whack, possibly a shorted tube or rectifier. I'd bet a tube. You may just have some weird timing. I remember making a current tester with a 100W lightbulb in series with my amp. It was an easy way to test for a bad tube. It's a gerald weber trick and it's out there on the web somewhere.
 

pfrischmann

Member
Messages
3,459
Thought about it a little more. If you feel comfortable, pull the chassis and inspect for burned or charred components, arced tube socket, burned rectifier etc.
Here's the current limiter I was mentioning. It's a cool way to test for shorted tubes. I don't know your level of comfort around amps but these guys can be lethal if you do not know what you are doing.

https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm
 

Rick Lee

Member
Messages
11,381
Pulled the chassis. Nothing is burnt or looks wrong. Amp sounded so awesome for a few mos. before last night. I don't have time this week to build that light bulb limiter, though have read that before and need to build one.
 

Rick Lee

Member
Messages
11,381
Thanks, but that's a 45 min drive each way, I am slammed this week and Hunt Amplification is my go to shop, which is 10 min away.
 

bgh

Silver Supporting Member
Messages
7,015
I'm going to throw in my vote that you have a not-yet-completely-dead tube. One that is dead and acts dead, but doesn't necessarily look dead.

I had this same behavior in a Dean Markley Spectra 212-T amp I had a number of years ago (I have since sold it). When a tube failed in it, it went in several stages. It was on life-support and caused the amp to have a very muffled sound. When it finally died, it still glowed somewhat, but gave no sound at all.

Not to mention it was one of the coolest tube failures I had ever seen. I was practicing in the living room. I had the lights off for some reason - don't remember why. When the tube checked out, it gave off the eeriest blue light I had seen.

OP, I hope it's a tube and not something wrong internally with your amp.
 

Rick Lee

Member
Messages
11,381
When I had two tube failures in one week, one continued to glow and the other redplated and looked like it was filling up with orange lava. This was my DSL50 and I was playing it dimed after biasing new Chinese tubes. I was sure it was going to explode and spew molten glass on me, but it just blew a fuse and then went dark.
 

tmac

Goldmember
Platinum Supporting Member
Messages
2,342
Replace power tubes without bias check in line and see if she blows then
 

Guinness Lad

Member
Messages
15,853
Your words, "Hot enough to fry an egg" I think one of the power tubes has been compromised. You only notice now because you're jostling things around.
 




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