#1
Hey guys!

Long story short: I have an 11 y.o. amp tube from a local manufaturer. It has 30W with 2 12AX7 on preamp and 4 EL84 on power amp.

I was playing today, and suddenly, its sound changed. It went from a nice sound to a very thin, high gainy, trebly, fizzy sound, most noticeable on the bridge pickup.

I tested with an Epi G400 with SD's JB on the neck, and Gibson LP with Classic 57+ on the neck.

Would you guys say it is faulty tubes? Caps? Something else?

I'd think twice before sending it to repair, since I started saving for a good amp (maybe Mesa, but this is for another thread).

Pls help a brother.
#2
It's most likely a preamp tube. I'd start by replacing the first one. Having extra tubes around is always a good idea anyway.
#3
I don't know everything about tubes and amps, and there are plenty of people here that know more than me, but I'd imagine that after 11 years, you'd need new tubes if you use your amp regularly. If I'm wrong here, someone feel free to correct me. I just know that my amp is 12 years old or so, and it definitely needs new tubes.

“We’re built of contradictions, all of us. It’s those opposing forces that give us strength, like an arch, each block pressing the next. Give me a man whose parts are all aligned in agreement and I’ll show you madness. We walk a narrow path, insanity to each side. A man without contradictions to balance him will soon veer off.”



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#4
If you love something, let it go.
Heavy metal rules, all that punk shit sucks. It doesn’t belong in this world; it belongs on fuckin’ Mars, man! What the hell is punk shit?
#5
As Roc said, start with a new preamp tube. Hell, your amp only has two of them, you might as well replace them both.

The other thing is that what you're describing, with the loss of low-end is what happens when your power tubes start to go. If you've had those power tubes for 12 years then I'm very surprised they're still working. In my experience, PTs don't last nearly as long as preamp tubes. I replace mine almost every year. Again, if you've gone 12 years without any new tubes, I think you'll be amazed at what a full-retube will do for you.

It's also worth mentioning that if your PTs are indeed that old, you may not want to risk playing with them for much longer. When they go completely, they can take out other components with them.
#6
Thank you very much for all your help! I really appreciate!

I will fully retube my amp, with new pre and power tubes.

Do you guys think I could re-bias the amp by myself?

Best to you, guys! Thanks!
#7
You can rebias the power section if you know how to do it and the amp is designed with an adjustable fixed bias (I know that last section seems like a contradiction, but the "fixed" bit just means the bias doesn't constantly change).

What's the model of the amp?
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Quote by Anonden
You CAN play anything with anything....but some guitars sound right for some things, and not for others. Single coils sound retarded for metal, though those who are apeshit about harpsichord probably beg to differ.
#8
Quote by oneblackened
You can rebias the power section if you know how to do it and the amp is designed with an adjustable fixed bias (I know that last section seems like a contradiction, but the "fixed" bit just means the bias doesn't constantly change).

What's the model of the amp?


It's a handmade amp by a local manufacturer. I think he based the design on a classic Vox, but I cannot remember which model...

I think I'd better send to a tech...
#9
Quote by YellowCat
It's a handmade amp by a local manufacturer. I think he based the design on a classic Vox, but I cannot remember which model...

I think I'd better send to a tech...
Why don't you change the tubes first, before you decide what to do?

You're assuming the amp needs re-biasing, which might not be the case. I'd want to know what it sounded like before I did anything else.

If you're intent on doing anything to the amp's guts, is the "original manufacturer" still around? You might be able to get the schematics from them.
Last edited by Captaincranky at Dec 21, 2015,
#10
I've had a similar problem where I just needed to clean the tube sockets. I was getting very low volumes and a weird nasty distorted type sound even on the clean channel. The first time I took it to a friend who works on amps and such and we pulled all the tubes and tested them, they were all fine, turned it on so he could hear the problem, and it sounded fine. His conclusion was that the sockets or pins on the tubes were oxidized or dirty and pulling them out and putting them back in scraped off enough gunk for it to make good contact.

It happened again a few months later and I dripped a tiny little bit of rubbing alcohol in each socket, inserted and removed the tubes a couple of times, gave it plenty of time to dry, and all was good again. I saw recommendations online to use de-oxit cleaner, but all I had was some radioshack electrical contact cleaner and wasn't sure about it and figured rubbing alcohol might be safer since it shouldn't leave any residue. It worked, so...

Of course, mine didn't start acting like that while I was playing, it had been sitting in a shed unused for a while and then it was like that when I turned it on again, but it's worth a try. Just be sure the amp is unplugged and be careful.
#11
sounds like dying tubes to me, but if you are strapped for cash clean them, if that doesn't fix it, replace the pre amps, and then the rest if all else fails. Thankfully it isn't too pricey and now is a good time to experiment with some different tubes if you are so inclined.
#12
Quote by Blicer
sounds like dying tubes to me, but if you are strapped for cash clean them, if that doesn't fix it, replace the pre amps, and then the rest if all else fails. Thankfully it isn't too pricey and now is a good time to experiment with some different tubes if you are so inclined.

But, but, but, if he changes the tubes, (model numbers), then it's more likely he'll have to re-bias the amp, which puts it into the shop, instead of a simple DIY plug n' play operation..
#13
Quote by Captaincranky
But, but, but, if he changes the tubes, (model numbers), then it's more likely he'll have to re-bias the amp, which puts it into the shop, instead of a simple DIY plug n' play operation..

biasing the amp isn't really that difficult, just don't stick your hands in there while the thing is on (i hope thats a given)
It is kinda like changing guitar strings, the first time is intimidating but after that is becomes pretty easy.

https://www.youtube.com/watch?v=harkrTLWDp0

here is a video thats pretty clear.

But if its that big of a deal you don't have too it was just a suggestion.
#14
Quote by Blicer
biasing the amp isn't really that difficult, just don't stick your hands in there while the thing is on (i hope thats a given)
It is kinda like changing guitar strings, the first time is intimidating but after that is becomes pretty easy....[ ]....
My post went to the TS' state of mind. He hasn't even bought the tubes yet, but he's hung up in biasing the amp. Methinks, to much information has been absorbed, versus too little actual understanding of the issue.

So, step at time. The bias adjustment should be considered a "tweak", and the histrionics and anxiety over it put aside, until the tubes are replaced. And I agree wholeheartedly the tubes shouldn't be replaced while the amp is either turned on, plugged in, or someone else is playing their guitar through it.
#15
The guy who built the amp is still around, yes. I'll contact him for the schematics.

I can't tell what happened, but the amp is back to life after a couple of nights turned off.

I will, however, try retubing the Pre-Amp. If it fails again, I will try the Power Amp... if it is not the same, I'll send the amp to a tech, or to the guy that built it.

Yes, it is too much information for someone who knows near to nothing about electronics. I can weld, take simple measures from a multimeter. But the reality is that I'm pretty scared/intimidated of messing with my amp, because of the high tensions, and such.

This amp just needs to last until the end of 2016, as I plan to buy something very nice!

In the meanwhile, I can use mine, also, to learn how to do stuff, like changing tubes, biasing, trying not to die from an electric shock. lol

I feel I should learn those things.

Thanks for everything!

Best!