Turned up my amp without a load connected

[bikescene]

I typically have my Plexi 50W amp connected to an attenuator or Suhr Reactive Load. Last week, I turned it on without any load connected in a moment of dumbness.

I wasnt getting any sound through my monitors, so I naturally turned up. Once the volume got about halfway, I heard a whooshing sound and the EL34s lit up like lightbulbs. Then I realized what happened and quickly turned off the amp. I blew the HT fuse and the tubes were probably shot.

Early this evening, I finally got in a pair of EL34s and a pack of fuses in the mail. I did some voltage and resistance checks without tubes to make sure the PT was okay. Luckily the amp was still working well with everything installed. I was worried that I blew the OT throughout last week, so today was a bit of a relief.

Just wanted to share.

 

[SKU]

probably

Did this a couple of times and everything was fine. Tube amps are really not that weak ...

 

[Mongillo19]

I’ve had the same primal reaction once..no sound = turn up volume.
In my case without consequences.

Memo for peeps who didn’t make this mistake yet;…..when there’s no sound with volume slightly open…the volume knob is not the solution.

So the act of turning it on without a load isn't the issue, but turning up the volume?

 

[Frodebro]

I always unplug any amps that don’t have a cab or load box connected to them. That is my reminder to myself to make sure that everything is connected before turning the amp on.

 

[Frodebro]

So the act of turning it on without a load isn't the issue, but turning up the volume?

The issue is the signal. An amp cranked to ten, but with no signal passing through the circuit still isn’t moving hardly any current. But strum a nice big chord through it, and the electrons start moving. Unless there’s no load…

 

[gearJunkie]

All's well that ends well. Now you have a fresh set of power tubes to enjoy.

 

[gearJunkie]

Ohm's Law

voltage = current * resistance.

with no load connected resistance is infinite (open circuit) so voltages spike and burn everything.

 

[bikescene]

Did this a couple of times and everything was fine. Tube amps are really not that weak ...

I was doing a bit of searching on forums, reading about how robust transformers were and trying to convince me that it was fine.

I might’ve been playing a single coil guitar. Not sure if the hum pushed enough single to cause problems. I don’t recall playing much, and was a bit distracted up until the light show. But maybe a strum was enough.

But thing are ok, and I’ll keep a better eye on the speaker cable.

 

[TimOwens316]

I did the same exact thing with a 1987X and I wasn't so lucky. It took out the power tubes, fuse, three resistors and a pot. Lucky for me I stumbled upon @Burger and he advised which components to check, and he was spot on, saved me a bunch of time. But dang, working on a PCB amp sucks.

 

[2dor]

I did this too on my first tube amp.
Had the cable going to the speaker not tucked in all the way.
Lucky enough, only took out the power tubes. The amp was fine after (happened 3 years ago).

 

[bikescene]

It is good to know that the protective components are doing their job. Good to hear that you guys got your amps back up and running too, when it happened to you.

I’m going to start disconnecting the power cable after powering off too. That was a good suggestion.