1959HW tube failure?

[King_Crimson]

Today my 1959HW suddenly started to sound strange while I was playing. Like a heavy fuzz, and the volume drops in between, with partially complete volume loss.

Can this be one of the tubes? I will try to replace each of the three preamp tubes tomorrow, but I don't have power tubes lying around.

Or can it be something different, not the tubes?

 

[PelliX]

Today my 1959HW suddenly started to sound strange while I was playing. Like a heavy fuzz, and the volume drops in between, with partially complete volume loss.

Can this be one of the tubes? I will try to replace each of the three preamp tubes tomorrow, but I don't have power tubes lying around.

Or can it be something different, not the tubes?

Yes.

But seriously, most likely are you output valves, followed by your preamp valves indeed. Check them optically to verify they're glowing normally and not redplating, this is important. It could be caused by a bad contact or a defective component like a capacitor, too, but rule out the most likely culprit first. How old are the current output valves?

 

[King_Crimson]

Thanks PelliX!
The power tubes are less than three years old. I don't use the amp very often, only some bedroom playing. But when I use it, it is set to high volume with attenuator as load.

 

[PelliX]

Thanks PelliX!
The power tubes are less than three years old. I don't use the amp very often, only some bedroom playing. But when I use it, it is set to high volume with attenuator as load.

A bit premature for one to fail, but certainly possible. I'd recommend an optical inspection and ordering replacements (worst case, you end up with spares that you will need down the line).

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[vtrain]

Preamp tubes are cheap (or, they used to be), I would replace them one by one and see if you find the culprit before replacing the power tubes (although definitely do a visual inspection of all the tubes before you replace anything). I had a similar issue happen and the cause was a very microphonic phase inverter tube.

 

[King_Crimson]

Thanks, I will try this, starting with the preamp tubes.

 

[Matthews Guitars]

You say you play at high volume with an attenuator. What kind of attenuator?

Your described symptoms sound uncomfortably like those of a failing output transformer. I hope it's not that, but be prepared for that possible diagnosis.

Attenuators...some of them...can be problematic and lead to output transformer damage.

 

[MonstersOfTheMidway]

@King_Crimson : Most likely its malfunctioning power tubes.

I had power tubes die on me slowly, but the sound quality was affected in a similar way to yours: big time volume drop, crappy distorted/fuzz sound (even on the clean channel). Put in brand new quad of EL34 and the amp sounded fantastic.

 

[King_Crimson]

You say you play at high volume with an attenuator. What kind of attenuator?

Your described symptoms sound uncomfortably like those of a failing output transformer. I hope it's not that, but be prepared for that possible diagnosis.

Attenuators...some of them...can be problematic and lead to output transformer damage.

I have the Boss Waza TAE. Not sure if this is one of the problematic ones. But can be possible.

 

[rolijen]

Boss Waza TAE is not the cause. If not the best, it’s certainly one of the best attenuators/load boxes/re-ampers/audio interfaces/studio effects units currently available.

Power tubes take a beating and sometimes tubes will go sooner than expected. I’m sure you know most of this already, but I would also recommend a quick visual inspection to see if one or more of the power tubes is red-plating and then I would recommend to shut down the amp and not play it until you can change out the power tubes. When power tubes fail, they can cause arcing/shorting internally and the high current can take out other components of the amp with them.

 

[neikeel]

You’ve had good advice
Always suspect a tube first.
If you have a spare ECC83 then take back off amp and play it. See if any odd flashes and sparks from output tubes as you play.
If not sub in a new pre into each position in turn. If no good I would open the amp up and scope it. You might not have that option so subbing in a set of new outputs suitably biased is reasonable. I do passive checks on screen resistors and a few other things too but give it s whirl. Hammering CP output tubes into an attenuator does shorten their life appreciably.

 

[Matthews Guitars]

I've had a power tube fail completely and the amp still makes sound. Not the right sound, but it didn't fade out.

In an amp with four power tubes, all four are producing a signal that makes it to the speaker via the output transformer. A single power tube failure should not be able to mute the amp even for a moment, unless it causes a high current draw that pops a fuse.

I had a Fender amp on the bench a few months ago and a power tube shorted out in spectacular fashion. Fireworks in the bottle. First time I actually witnessed it with my own eyes. It was a Svetlana 6L6GC. The amp continued to generate sound (signal generator was running) after the fireworks were over. Upon inspection of the now dead tube, compared to its brother, I could see that wire connections
in the bottom are of the tube had literally been melted away.

If the whole signal is fading out and coming back, I'm sure that some power tubes are still operating.

 

[ken Tucky]

Probably a tube as others have stated. It usually is. One thing to keep in mind is that when using attenuation, you may be bringing the volume down to accommodate your ears but you are still punishing the tubes as if things were loud. Subsequently there is harder wear on tubes than playing the amp with the volume set low and using a pedal or a MV to provide gain/distortion. And because using attenuation alleviates punishment to our ears, we tend to play more often and for longer periods than if the amp were audibly loud. Hence tubes usually wear out faster with attenuation and also can expose a weak valve early. If it turns out to be a power tube replace them all with a new matched set and then have the amp biased properly by a tech.

 

[King_Crimson]

I replaced the preamp tubes one after the other, problem still there. I have also optically checked the power tubes. They look normally glowing, no red plating.

As you proposed, the next step would be changing the power tubes. I have a second amp with EL34 (2555X). Would it be safe to use its power tubes for a short test, or could they also be damaged by the 1959?

Or can I put the 1959 tubes into the 2555X to check if they work or fail there?

 

[neikeel]

Do you know how to bias tubes?
Do you have a voltmeter?

 

[King_Crimson]

Do you know how to bias tubes?
Do you have a voltmeter?

Yes, I have a measuring adapter for the tube socket and a voltmeter. I did it only once years ago on my old 6100LM, so I will search and read instructions first. As electric engineer, I am aware of the high voltages. At the end I maybe will bring it to a tech that has more practice on it.

But the idea was to use the 2555X tubes without bias for only a short time, just to verify if the power tubes are really damaged.

 

[PelliX]

Or can I put the 1959 tubes into the 2555X to check if they work or fail there?

I'd be inclined to try it the other way around, but yes, within reason. For anything more than a couple of minutes of testing without an attenuator at 'normal' levels, you should re-bias the amp.

Would it be safe to use its power tubes for a short test, or could they also be damaged by the 1959?

They could of course be damaged, but it's quite unlikely unless the bias is waaaay off.

If you give the amp a bit of 'percussive maintenance' like a slap on the side or the top, does the sound change? I'm not suggesting to get out a sledgehammer, but just the kind of slap you would use to swat a fly on your leg, say.

Any chance of getting the current bias readings?

 

[neikeel]

Yep
I’d see what the present tubes are biased at.
You could sub the other tubes in (or as suggested try old ones in other amp)
That combination will tell you a lot.

 

[King_Crimson]

I tested the tubes in the 2555X now, which is very easy to bias. They work... So I think the failure must be a different part, maybe the output transformer, as suggested above. Will have to look if there is an amp tech in my area...

 

[PelliX]

I tested the tubes in the 2555X now, which is very easy to bias. They work... So I think the failure must be a different part, maybe the output transformer, as suggested above. Will have to look if there is an amp tech in my area...

Do whatever you're comfortable with, but I would at least check the bias on the 1959, give it a slap or two to see if it might be a bad connection somewhere, perhaps a visual inspection of the guts. If none of that yields, then you *may* have an OT on the way out as @Matthews Guitars mentioned...