Anyone had a similar valve amp issue?

[needsmorecowbel]

I've Lately Been getting this weird kind of metallic muddiness/ distortion/ oscillation when playing through my 60 watt valve amp (Hughes and Kettner 6l6). It is only select notes on select strings but it is driving me bonkers. When you play a chord you can't really hear the metallic ring/ oscillation but when you play individual notes with the amp up fairly loud on some occasions the bloody thing just rattles/ vibrates madly and when the sound of the note subsides you hear this very faint metallic rattle that decays with the note... These amps are fairly prone to reverb issues. But could also be the tubes. Anyone had a similar kind of thing happen? I'll post a sound file in a tick

I've never had to change the tubes and usually use the amp on the clean channel (nor do I plan on changing the tubes myself- leave it to a tech...)

Strings
E Frets 5-12
A Frets 3-16
D Frets 3-11, 15-17
G Frets 0 -7
B No Frets
E 0-6, 11

Stu

[needsmorecowbel]

Mic on Camera isn't picking up the frequency/ distortion will have to use the Midi interface and recording Mic Tomorrow to pick it up.

Stu

[Dekka]

Hi Stu

My Marshall does a similar thing. When I'm tuned to 440 and play an 'A' it makes a buzz/vibration that sounds like the speaker cone has crapped out. The Celestions, however, look a good as the day they were made. My electronics guru says it is most likely a tired tube issue or a poorly seated tube. I haven't had the bucks to do the fix as yet but I reckon that will fix it.
There's a lot of useful info about microphonics in tubes on this link:-

http://www.eurotubes.com/eurotubes-FAQ- ... sing.htm#3.

[Nick]

Issues I've had with with my valve amp have been rectified by fitting new tubes. I have a Fender Hot Rod Deville (full tube amp) and was having all sorts of subtle issues with it for quite a while until a friend, who designs and builds his own range of amps, installed Russian made tubes (can't think of the brand offhand) muttering something about the "quality" of factory fitted tubes and it's run as sweet as a nut ever since. So might be trying that as a starting point, and if you've had the amp for a while, treating it to a new set wouldn't do it any harm anyway

[kiwigeo]

Try adjusting the steam pressure on the boiler

[DarwinStrings]

Try adjusting the steam pressure on the boiler

I wonder if guitar amps are the last piece of electronic equipment to use valves.

Jim

[needsmorecowbel]

Haha thanks guys. Having had a read around it looks like the sympathetic vibrations could be causing the internal filament of the valve to rattle towards the end of notes with more bass.

Also interesting to see some on the web referring to Combo amps are "TUBE DEATH FACTORIES" as the valves are far better off being further away from the vibrations of the speaker...

The options are to:

1 - get several heat resistant silicone rings to put around each of the tubes (don't know if these actually do anything),
2 - change the tubes
3 - ensure all of the screws on the amp are tight
4 - ensure there is something between any metal surfaces that may be vibrating (thin rubber/ foam strip)

Stu

[needsmorecowbel]

If anyone can suggest a good source of Heat resistant Silicone O Rings Would be much appreciated have a few numbers I'll call around tomorrow.

[GregL]

Hi Stu,

Try Carol and Mal at Evatco for (what they call) tube rings:

http://evatco.com.au/miscparts.htm#trings

Thanks,
GregL.

[needsmorecowbel]

Thanks Greg, I found out it is not a tube issue through some testing...

Stu

[GregL]

Hi Stu,

What was it? Reverb, combo-related, something else?

Thanks,
GregL.

[needsmorecowbel]

Greg, I think it is Combo Related possibly reverb. It sounds too metallic for a blown speaker (very spring like or similar to the sound of a filament on glass). I gently tapped the tubes with a piece of plastic (chopstick) whilst playing (at the suggestion of a repairer and some forums-maybe this is a troll who knows..) and nothing happened. I also changed out the preamp tubes at the suggestion of a few repairers. Then I put my ear closer to the amp and it appears to be coming from inside the housing near the speakers where I would expect the reverb tank to be.

Potential Issue:
1. Reverb Issue (replace the tank $66 for the part + Labour p/h ($65-85))
2. One of the 12AX7 plugs was a bit loose when I replaced those tubes...
3. Internal speaker issue
4. Problem with it being a combo amp and having the reverb tank & tubes so close to the speakers

[needsmorecowbel]

I have a smaller amp of the same series (20 watt instead of 60watt) that had pretty much the same issue 11 months after I bought it (but it just went back to the factory and came back sounding like new and still works great). I love the tone these amps produce too much to just part with it and make it someone else's problem.

I might even start researching if it is possible to just separate the combo into two sections by making a wooden housing for the head. (reverb and valve head and use the original speaker cab. if the reverb tanks are going to be a reoccuring issue in these amps that costs money might just have to opt for a different solution/ alteration to the design (reverb pedal/ different reverb tank (according to the specs of the amp/ circuitry)). Or get someone to teach me how to replace the bloody things...

Stu

[GregL]

Hi Stu,

I have made a couple of valve amps, and have frequented some valve amp forums, but I'm definitely not an expert.
I assume the unit is out of warranty? If it's still in warranty - take it back.
I assume the amp worked OK when new? ie the problem started some time after you started using the amp, the amp did not have the problem from new?
1) "Chopsticking" is a recognised technique (and useful in the right circumstances);
2) If you have swapped preamp valves with no change then it's not a preamp valve problem;
3) Do you have the same issue in both channels? (I assume it's a 2 channel amp);
4) Do you have the same problem when the reverb is turned off?;
5) Loose valve socket is a possibility;
6) Have you got an external speaker you can try, to eliminate (or confirm) internal speaker problem?;
7) The reverb tank should be visible and accessible in the bottom of the cabinet;
A combo amp (ie enclosure includes speaker) is not the ideal environment to operate spring reverb, because of vibration;
9) Converting a combo amp into a seperate head and speaker box is not particularly difficult - but you have to make (or buy) a head enclosure and a speaker box.

Thanks,
GregL.

[needsmorecowbel]

Greg,
I bought the amp second hand rather cheaply $800- I tested the amp for this very issue as I realised it was a possibility as my lesser wattage amp of the same series had the same issue...However SOMEHOW the issue surfaced after I bought it (even though I was looking for the issue upon testing/ before purchase). I however do not regret the purchase as they are nice amps despite their little idiosyncrasies. I bought the amp to test/ demo guitars I build and it doesn't cost much to replace a reverb tank $60.

1) The chop sticking did nothing...But it is good to hear it is a recognised technique as an amp repairman suggested it when I bought the replacement preamp tubes (Tung-Sol) off him.
2) Preamps are not the issue I agree
3) You can hear the oscillation/ rattle on both channels
4) Reverb- the oscillation/ metallic noise decays over a longer period as you would expect with the reverb on full. With the reverb off the oscillation still occurs.
5) Loose socket is probably not the issue as it wasn't as loose as I thought when I decided I'd switch the new Preamp tubes around to note any effect. No Effect
6) I will plug in my lower wattage amp (have to go and buy an extension power cable) and try that to confirm/ eliminate speaker damage.
7) The Accutronics Spring Reverb Tank is NOT on the bottom of the cabinet (suggesting it is up near the tubes ). A forum on electronics suggested this tank was actually "transformer driven reverb". Although I can't confirm that. The location of the reverb tank so close to the speakers is perhaps ill conceived...(Hence I was suggesting it may be a design flaw)
9) Cheers for the info Greg. I will continue researching what to do about it (I'm in no rush to fix it)

Let me know if anything I've posted above strikes you as odd.

The only other tiny little thing with the amp is that it turns on to the gain channel when the footswitch is not plugged in (could this be a short with the electronics of the head?). The fix to this problem is to have a footswitch plugged in all the time and that way it defaults to clean like it should. I sent through a support ticket to the company but haven't heard back.

[GregL]

Hi Stu,

Like I said before, I'm not an expert, but your answer to 4) would seem to indicate that the problem is before the reverb (or a problem with the reverb itself). I would guess that the reverb works on both channels? If so, the reverb is after the preamp and before the power amp - a common location for effects. Not much help, but it gives a better idea of the topology of the amp.
What specific model is it? Is it a Statesman Series STM Dual 6L6?
These days, most "production" valve amps are built around somewhat flimsy PCB's, prone to early failure (caused especially in combos by vibration).
"Traditional" reverbs are normally "transformer driven".
Assuming that the reverb uses a reverb tank, and it's not at the bottom of the cabinet, see if you can find where it is - it may be on one of the side walls of the cabinet. If it's not on a side wall, the only other place it could be is in the amp chassis, which is not ideal. OR it might be a digital effects unit, in which case it'll just be a chip on the PCB.

Thanks,
GregL.

[needsmorecowbel]

I understand you may not be an "expert" but I'm sure you'd know a hell of a lot more than I and I'm finding this all very informative.

Reverb Tank/ housing appears to be in the chassis as it is not on the bottom of side walls as far as I can see (I put an inspection mirror inside and shone a torch) . It is not a digital effect. Pretty sure it is transformer driven as people were complaining on a forum about why amp companies use this type of reverb when alternate types of spring reverb are so readily available and less
"traditional"...

That is the one... is the only Statemsan DUAL 6l6 60 watt model:
http://www.hughes-and-kettner.com/produ ... DUAL%206L6

I'll have a play around with it a little more and report back. Apparently I can plug my guitar directly into the FX loop return and that should cause the guitar to skip going through the pre amp this way I can figure out very roughly where the issue is. I'll also test the speakers in the morning

Stu

[GregL]

Hi Stu,

I should have said this at the beginning, but BE VERY CAREFUL! when working on valve amps. They usually have *LETHAL* voltages inside, so if you're not comfortable, take it to a tech. If you do delve inside, then leave it plugged in but turned off for a few hours first to make sure all capacitors have drained. Another good trick is to always have one hand in your back pocket, ie only use one hand when working near high voltage, then if something untoward happens, at least the current doesn't go through your heart on it's journey.
That said, you should be able to unscrew the back panel of the cabinet and see what's where.
Also NEVER switch on a valve amp unless it is plugged in to a speaker. Valve amps need a load connected when turned on. So when testing with an external speaker, make sure it's plugged in before turning the amp on.
Yes, you should be able to plug your guitar (or other signal source) into the FX return to bypass the preamp. It won't sound great, but it should make a sound.

Thanks,
GregL.

[kiwigeo]

I gently tapped the tubes with a piece of plastic (chopstick) whilst playing (at the suggestion of a repairer and some forums-maybe this is a troll who knows..) and nothing happened.

Go on ya pussy...tap the tube with ya finger

[needsmorecowbel]

Totally Understand Greg this isn't the first place I posted, I've only taken the cover off that allows full access to the tubes. I have only ever touched the tubes with my hand after the amp has been plugged in (but turned off at the wall) after 1 hr as I wanted to let any residual current drain away...Also used the one hand rule in that instance just to be safe. I've mainly been poking at the tubes when they are on with a chopstick. However thanks for the warning!

I'll do a bit more troubleshooting today and let you know where I get..

Stu

[Nick]

Another good trick is to always have one hand in your back pocket,

So Amp repair is very similar to luthiery then Greg? except in Luthiery it's usually to go for the wallet and not a safety reason
(excellent tip by the way and one all of us could take note of whenever working around power supplies and Capacitors!)

[GregL]

Hi Nick,

Your hand has to head for the wallet with amps too, on occasions! A good DIY valve amp will set you back about the same in materials as a DIY acoustic guitar, and if you blow an output transformer, that can hurt cash-wise too.

Thanks,
GregL.

[needsmorecowbel]

Hypothetically what timber would you use for a head box? Would hardwood be okay... like Black Heart Sass or myrtle or blackwood? Or would it be better to just use something like Birch Ply? Seeing as it is the amp head and not the cabinet I would have thought that you could have used quite a range of timbers...

Stu

[GregL]

Hi Stu,

You can use anything for an amp head cabinet. Depends what you want to do. I like timber, so I have made an amp head (and speaker cabinet) out of Australian red cedar. Alternatively, a lot of people cover the timber with "tolex" - sort-of textured vinyl (your Hughs & Kettner is tolexed), in which case the type of timber doesn't matter.
(I can post a photo here of the amp I did with red cedar if you're interested - tonight from home)

Thanks,
GregL.

[needsmorecowbel]

Sure thing. Look forward to seeing a pic of it

Stu