#1
About two weeks ago I noticed my amp was running hotter than usual. I figured it was my imagination and forgot about it. Turns out I was mistaken...

About a week ago, after replacing a preamp tube, I noticed this odd inconsistency in the noise (background hiss). It sounded like it was getting some kind of interference. I was like, oh great, they sent me a bad preamp tube, so I took it out.

So yesterday I went in and was moving some tubes around (been trying different brands) and when I turned the amp back on I was getting all kinds of crackling and popping. I figured I didn't seat a tube right so I pulled them all and re-seated them.

When I turned the amp back on it was even worse! While standing there, guitar in hand, wondering what's gong on, there was a semi-loud pop and a short buzz and a flash of light came through the top vent!

So I go back in, re-seated the power tubes this time, and turned the amp back on. Still the crackling with even the slightest touch to the amp. Damn. So I look in the top vent and there was a rather lovely blue strip of light emanating from the center of one of the power tubes.

Luckily I picked up a spare set when I ordered the preamp tubes. Popped them in and all is well again.

Is that a "normal" way for a power tube to fail? I figured they'd go microphonic before they outright failed like that. Even more strange to me is that after the flash of light they still worked (somewhat). I can't see any damage to the tubes either (no burnt plates, nothing) or to the amp.

I thought power tubes lasted longer than this too. They had been in there for about 8 months but I've only cranked it up once since they were put in. Otherwise I run at maybe slightly louder than bedroom level. I've heard EL84's aren't the longest lasting power tube but I figured I would get at least a year out of them.

I'm all paranoid now about my amp blowing up when this set fails lol
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
#2
Yeah that's how they fail, sounds like you just need to notice the warning signs next time.

But 8 months? That sucks. Check the bias I guess.

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#3
It sounds like you really need to bias your amp. Your amp is driving the tubes too hard so lower the bias a bit.
#4
Well for all I know they weren't even new. I blew this amp up once and when it came back from being repaired there was a set of EHs in there. I'm trying out these new production Mullards now, so will see how long those last.
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
#5
Quote by Myaccount876
It sounds like you really need to bias your amp. Your amp is driving the tubes too hard so lower the bias a bit.


Before a couple weeks ago it seemed to run reasonably cool. I would describe is as warm, whereas after I would describe is as hot.

I'm glad you said that though because I forgot the bias the Mullards... They're running fairly cool though.

Last time I did this though I almost electrocuted myself
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
#6
Sounds like they were 'current production' JJ EL84's...


The preamp tubes are heading downhill too...

Thursday, February 23, 2012
Tube Test - JJ803S
http://la-economy.blogspot.com/2012/02/tube-test-jj803s.html
Last edited by BurstBucker Pro at Mar 8, 2012,
#7
They were Electro Harmonix. Probably made in the same factory though for all I know (they're all owned by New Sensor now).
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
#8
Wish the NOS tubes of old were still in production...

We can put a man on the moon, but cant seem to make vacuum tubes like they did 50 years ago.

Sad!
#10
^ you are a tool.

Why do you just get on here and blast JJ's?
#12
What amp is this?


And yes. Tubes will fail in all sorts of weird and miraculous ways. They don't always go microphonic. Going microphonic is normally an indication that the vacuum seal is failing. That's not all that can go wrong in a bottle of glowing metal.
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Last edited by Cathbard at Mar 9, 2012,
#16
Quote by Cathbard
What amp is this?


I don't think it is one brand of amp so much as it is the current production 12AX7's, not meeting the spec for a 12AX7.

And being microphonic.
#18
The Shuguang EL34's are getting surprisingly good. Give them a few years and they'll probably be the best thing out there.
I have a set in my JCM900 that some guy pulled out of a hifi to "upgrade them" to Russian valves. And what did he buy? EHX. I just Well, I managed to score them cheap so all's good.

Unless I could find nice NOS tubes in that (and NOS EL34's are getting crazy expensive) I'd be tempted to go for SED =C=. Otherwise JJ.
In the preamp I'd go for JJ ECC803 if you didn't have nice NOS preamp tubes. They are worth hunting down though. British Mullards, Amperex, Telefunken, even American ones like RCA or Phillips. That is the sort of amp that will really benefit from them.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#19
Quote by BurstBucker Pro
Then live in your ignorance, and keep thinking it's me -vs- JJ.


I am just trying to get you to rant in 3rd person changing the color every paragraph. Again.

My last set of 12AX7's were great, hopefully the next set will be too.
#20
Quote by Cathbard
What amp is this?


It's a Jet City JCA2112RC (JCA20H combo).

I biased it and surprise, surprise! It sounds exactly like the EH's! lol

I let the amp run for a bit though and turned the lights off and looked in the vent--yeah, the plates were slightly red and the amount of heat seemed about the same as the EH's after they got hotter.

Quote by BurstBucker Pro
Did you watch the video? Very educational by people in the know.


I did watch it, and I knew there was something odd about all these different brands coming from the same company. Seems they're just binning the tubes and charging NOS prices for them.

That video sold me on NOS though. I doubt I would buy NOS power tubes though, but I think I might check out some JAN GE/Sylvania preamp tubes. I'd like to try some of these Telefunkens but I think I'll wait 'till I graduate and get a couple jobs.

Something is wrong here though. A few months ago V2 "died" so I swapped it out with another I had taken out. Now I put a 12AT7 in there (Tung-Sol) and that one wasn't working when I turned the amp on awhile ago! I swapped it out, but then on a hunch I put it back in and it works! I think I might have a loose solder connection on the socket or something.

But, I just ordered a new amp anyway. I'm going to check out one of these Bugera 1960 Infiniums. Been hunting for a plexi sound on the cheap and this could be it. The Jet City is probably going to help me with my soldering skills soon lol

Now I just need one of these so I can kill more expensive tubes even faster!
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
Last edited by Prime2515102 at Mar 9, 2012,
#21
Sorry, I was talking about it as if you had a 65 amps amp.

JJ ECC803's may not be so good in that. They can have a tendency to be a bit too microphonic in a combo. I'd probably just chuck JJ ECC83S tubes in there.

It's a good idea to check your bias every now and then rather than just when you first stick them in. It can drift a fair bit over time. Certainly a skill worth having.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#22
Quote by Cathbard
Sorry, I was talking about it as if you had a 65 amps amp.

JJ ECC803's may not be so good in that. They can have a tendency to be a bit too microphonic in a combo. I'd probably just chuck JJ ECC83S tubes in there.

It's a good idea to check your bias every now and then rather than just when you first stick them in. It can drift a fair bit over time. Certainly a skill worth having.


Yeah, I'm going to start doing that. I just ordered a bias probe that plugs into the tube socket so I minimize electrocuting myself.

I do have an 803S and it sounded pretty good except the highs were a bit fuzzy (this amp has a tendency to be a little fuzzy anyway though).
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
Last edited by Prime2515102 at Mar 9, 2012,
#23
In that case I'd say JJ ECC83S even moreso then.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#24
Ok, everything has changed now... lol

I don't know if these Mullards had to break in or what, but this amp has never sounded this good! It's a bit less spongy feeling than before, but that's a good thing because it felt out of control (I overdrive the shit out of it with an MXR M77 and 10-bad EQ--noise be damned!). I didn't think that non-overdriven power tubes could make such a difference; it's like they effected the preamp somehow. I dunno...

I want to dime this thing so bad right now it's making me sick! lol

Now I have to go back and retry those other preamp tubes and see what I get. I put a lower-gain 12AT7 in V2 the other day also (the first triode is 5db lower than the other one I had in there) so maybe that'll help with the fizzies.

After I get some sleep... ha...
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude