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I have an Epi Valve Jr which came with some Mesa tubes (Sovteks?). I switched them out with some RCA blackplates - actually I got a 12BZ7 and a NOS RCA EL84. They sounded great for a few days then started to sag. I pulled the tubes out and the EL84 burned my hand. I could swear I switched them out hot before but not this time. I wonder if the RCA 12BZ7 fucked the whole amp up. Or whether it was the EL84. Anyway, I stick the Mesa back in it and the EL84 is super hot. Yo, help a befuddle out will ya?

You shouldn't really switch out tubes while they are hot, just not a good idea. Yes the EL84's get hot in Valve Juniors. Both tubes do

good, thanks for that
I have a set of mullard 12ax7 and el84 and I didn't want to fuck them up

No problem dude. I'd wait at least a good 20 minutes before trying to pull the tubes

yah, all tubes in an amp should be a little hot.

In my other two amps they don't get as hot. I can switch both tubes out of my Peavey Nanovalve and they don't burn.

Stock Valve Juniors run hot. My VJr cooked when stock. It was dissipating 13.75 watts on the EL84. Max spec is 12 watts. That will shorten the life of the tube.

The options are to either use cheap tubes and not be upset when they die, or modify the amp to be within spec. The modifications aren't necessarily hard, but you are dealing with a tube amp.

For my VJr, I added a 20-ohm resistor at the power mains, since all of my voltages, including the heaters, where high, and replaced one resistor (R14, 240-ohms). Now it dissipates 11.5 watts, and runs much cooler.

I can put good tubes in it without worrying that my amp will eat them.

Mike

Shit, is there an easier way to cool it down for idiots?

http://geofex.com/Article_Folders/vintvolt/vintvolt.htm

That's as easy as it's gonna get if you're not going to mod the amp itself. Probably not a good idea for every modern amp, but since I think Mike's experience of the VJr is typical that all the voltages are high, scaling it all down at the input voltage should work well.

If you need to swap tubes without cool-down time, oven mitts. And especially when hot, pay attention to Spaceritual's advice.

EL84s get hotter than any other tubes i've dealt with, and they do it almost immediately. in less than two minutes they're hot enough to blister your fingers, while i could pull hot 12AX7s all day long.

good to know

Definitely don't touch EL84's when they're in use or after they've just finished being used. They're almost as hot as a light bulb. They might not immediately scold the skin like a 100 watt bulb, but it will hurt and be dangerous.

EL84 amps are typically biased really hot so yes, they burn. They burn a lot.

GardenoftheDead wrote:EL84 amps are typically biased really hot so yes, they burn. They burn a lot.

That's good to know. I fucked up and bought an EL86 by accident and then one day I looked at it and that fucker was on fire. Then ever since I switched back to the right tubes and they were burning hoot and I wondered if I fucked the amp up but now I think not. That NOS RCA 12AX& they said had %70 really was a dud cause it was like half volmume.