#1
I'm almost certain my RG50TC needs retubing, due to it sounding incredibly fizzy and as if it's lacking balls.. Is that a sign of needing new tubes?

I think the previous owner said it has EHX tubes in it, but I haven't opened it to check yet. I'm unsure if I like these tubes, as I was never particularly partial to the sound from them..

The amp uses 2 EL34 tubes and 4 12AX7EH tubes, is it alright to get any brand without rebiasing? Or do I have to get the same ones?

Is rebiasing something I can do myself?
Last edited by dandadog at Jul 31, 2009,
#2
You can get any brand, but you should rebias even if you get the same brand. Unless you have a tester, there's no way to know that the tubes you're getting have the same operating voltage as your old ones. You could rebias it yourself -- there are directions easily available online -- but sometimes it's better to let a technician do it the first time and show you how to do it. Or, just don't rebias it. It's not a life or death thing.
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Last edited by Dirk Gently at Jul 31, 2009,
#3
They are EHX tubes. Which tubes do I need to replace? These can't be much more than a year old, so is it the preamp tubes causing the problem or the other 4 power amp tubes?
#4
The 12AX7s are preamp tubes, not power tubes. The EL34s are the power amp tubes, and the ones you need to rebias.
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#5
Quote by Raijouta
The 12AX7s are preamp tubes, not power tubes. The EL34s are the power amp tubes, and the ones you need to rebias.


Ah, ok. Which should I replace? Having to replace all of them after a year seems silly, so which would be causing my problem? Is there a way to test dodgy tubes?
#7
There are a few ways.

If it's a multichannel amp, and you have problems in one channel but not the others, that's a sign of a bad preamp tube. If it's a problem in every channel, it could be your phase inverter preamp tube or your power tubes.

You can do the tap test -- get the amp warm, turn it on, give yourself a decent amount of volume, and then go get a pencil. Tap the tubes with the pencil (preferably the eraser end). If a tube causes noise to come through the speaker, such as a crackling or static, it's bad.

Additionally, there's visual inspection. A bad tube will sometimes glow a different color than the other tubes. There are also arcs to look for, which are little sparks of electricity inside the tube.

A bad preamp tube can be replaced individually; bad power tubes have to be replaced in pairs.
Hi, I'm Peter
#8
Quote by Dirk Gently
There are a few ways.

If it's a multichannel amp, and you have problems in one channel but not the others, that's a sign of a bad preamp tube. If it's a problem in every channel, it could be your phase inverter preamp tube or your power tubes.

You can do the tap test -- get the amp warm, turn it on, give yourself a decent amount of volume, and then go get a pencil. Tap the tubes with the pencil (preferably the eraser end). If a tube causes noise to come through the speaker, such as a crackling or static, it's bad.

Additionally, there's visual inspection. A bad tube will sometimes glow a different color than the other tubes. There are also arcs to look for, which are little sparks of electricity inside the tube.

A bad preamp tube can be replaced individually; bad power tubes have to be replaced in pairs.



I'm unsure if it's both channels, there's definitely a problem with the gain settings, I'm not sure if there's a problem with the clean channel. It breaks up far too early, so I can't get much volume onto the clean channel to test it properly.

I'll try the tap test.
#9
If you replace all of your tubes, they should all wear out at the same pace, so you won't have to go through the trouble of finding the bad tube next time.

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#10
Right, did the tap test.

On gain 1&2, from tapping one of the EL34's I got nothing, and the other one seemed to rattle on the inside, and then one of the 12ax7's when tapped made a small high pitched sound, and the other 3 did nothing.

Upon going to the clean channel, BOTH the EL34's made a horrible noise through the amp when tapped, but I can't remember if the 12ax7's made any unusual noise.

I then went back to gain channels, and they had the same noise. I occasionally notice a large pop when going from the clean to the gain channels on the first time of switching after turning the amp on.

So the next step is to replace the EL34's, yes? Where is the cheapest place to buy tubes?
Last edited by dandadog at Aug 9, 2009,
#11
Preamp tubes last several times longer than power tubes, so the only reason to change them is if you're unhappy with your tone or are getting microphonics/noise.