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[mrbrown49]

This stuff is hard enough to diagnose in person, let alone, remotely over the internet.

[jjang1993]

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[WRGKMC]

Trying different tubes is still am option. I have used older groove tubes for years but not since Fender bought them and moved manufacturing to China. You may want to try something like a Sovetec or JJ for the power tube. The JJ 12AX 7 should be pretty good but there again, something like an Electro Harmonics has some of the best specs going.

 

Using weather stripping between the chassis and cab is a good move, except in cases where they put either mesh or foil on the inside of the cab. That foil acts to reduce hum and the metal chassis has to contact it so you couldn't use any kind of rubber because it acts as an insulator and your hum level will go up without the electrical contact.

 

The fix would be to make a metal cover for the inside of the chassis, then suspect it, but this is a small combo so none of this may matter.

 

My suggestion would be to get tubes that are low microphonic. Then get some tube "keepers" They used to use the old spring loaded cans for this but they may have some new ones that will absorb sound better and reduce the vibrations of the glass bottles.

[DeepEnd]

Trying different tubes is still am option. . . .

 

. . . My suggestion would be to get tubes that are low microphonic. . . .

I checked the reviews at thetubestore.com and for 12AX7's EH is supposed to be very good at eliminating microphonics. For 6V6's the only review that mentioned microphonics (as in their absence) was Tung-Sol. Probably as good a place to start as any.

[jjang1993]

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[DeepEnd]

Sorry, we cross-posted. See my post above.

[WRGKMC]

This site rates preamp tube microphonics. Its pretty good for rating gains and tones too.

 

https://www.tubedepot.com/tube-comparison-tool

 

You can use this one for Tone as well.

 

https://www.tubesandmore.com/tech_corner/12ax7_comparison_of_current_made_tubes

 

These were the old style tube keepers many amps used. They were spring loaded to keep the tube tight and reduce microphonics. They also helped reduce hum. https://www.tubesandmore.com/products/P-SS9-325

 

 

They make other types too.

 

http://www.mojotone.com/amp-parts/Retainers-for-Vacuum-Tubes/EL84-Power-Tube-Spring-Retainer

 

I haven't tried these but these tube dampers may be all you need to fix the problem. They are supposed to dampen the tube so it doesn't vibrate so much. You can pot one or two on the tube to kill oscillation. These are for the 12AX7 tube. (These are high temp silicone so don't go trying to use rubber bands as a substitute.

 

http://www.amazon.com/Cary-Thickness-Dampers-Silicone-Shuguang/dp/B00KMPCYOS/ref=pd_bxgy_267_img_2?ie=UTF8&refRID=1W3D6CH1K2PJ9TSMAHZ3

 

 

You can find these for larger tubes too.

 

http://www.ebay.com/itm/VACUUM-TUBES-AMP-DAMPERS-FOR-6SN7-6SL7-GZ34-7591-6V6GT-5692-6C10-SMALLER-EL34-/371617560556

 

 

http://www.ebay.com/bhp/tube-dampers

 

 

There are others too.

 

These look like they might do a better job. May save on tube life too.

 

 

http://www.needledoctor.com/EAT-Tube-Cool-Dampers

 

and still others

 

 

 

This one is supposed to kill ultrasonics. http://herbiesaudiolab.net/rx.htm

 

 

An more - http://www.jacmusic.com/accesories/Duende/index-WT.html

 

And More http://www.canuckaudiomart.com/details/648945667-tubes__herbies_tube_dampers/images/337904/

AND MORE http://www.canuckaudiomart.com/details/648945667-tubes__herbies_tube_dampers/images/337904/

 

You get the idea. I'd start with a low microphonic tube however, These are simply band aids for microphonic tubes, usually old vintage ones that still have life in them.

 

 

 

[jjang1993]

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[DeepEnd]

Thanks for the info! I currently have 6 of those silicon rings on the preamp tube and 4 silicon rings on each of the power tubes. Maybe getting some quality tubes and metal tube shields will help.

AFAIK, metal shields are to prevent electromagnetic noise. I don't know whether they do anything for microphonics. They can also affect the sound of the amp. The fact that you have the problem with silicone damping rings already installed is a bit concerning. They're supposed to dampen airborne vibration but it sounds like you have issues with vibration conducted through the amp's chassis. I don't know how well they're supposed to work with that but if your amp is any indication I'd say "not very."

[mrbrown49]

AFAIK, metal shields are to prevent electromagnetic noise. I don't know whether they do anything for microphonics. They can also affect the sound of the amp. The fact that you have the problem with silicone damping rings already installed is a bit concerning. They're supposed to dampen airborne vibration but it sounds like you have issues with vibration conducted through the amp's chassis. I don't know how well they're supposed to work with that but if your amp is any indication I'd say "not very."

 

The metal can looking ones have spring inside that pushes on the tube to tame vibration as well.

[WRGKMC]

Thanks for the info! I currently have 6 of those silicon rings on the preamp tube and 4 silicon rings on each of the power tubes. Maybe getting some quality tubes and metal tube shields will help.

 

If you've done that already then I cant see it being anything but the tubes. you may have bought the tubes as new but there's always the possibility someone bought a new tube and sent back a used one.

 

I did a little more investigation and see the The Super XD is not a pure tube amp, its a hybrid with a solid state front end. The tubes are not likely the cause of the issue.

 

My opinion has always been the same when it comes to Hybrids. When you mix high voltage, high temperature tubes with low voltage low temperature solid state devices you'd bound to have a much higher mortality rate. The noise may have nothing to do with the tubes whatsoever. it may be an issue with a cracked solder joint on a chip, transistor, cap, resistor etc. All you're doing by insulating the chassis is preventing that cracked solder joint from vibrating. It may simply need re-soldering.

 

If it is the tubes the amp only uses a 12AX7 for an inverter and two 6V6 for power amp are tubes. The 12AX7 isn't being used as a preamp so the possibility of it inducing microphonics isn't likely.

 

You may want to try a 12AT7 tube for the inverter instead of a 12AX7. The best 12AT7 I could find when I did my recent retuning were the JAN-Philips 12AT7WC. http://www.thetubestore.com/Tubes/12AT7-ECC81-Tube-Types/JAN-Philips-12AT7WC

 

These are New Old stock (NOS) Joint Army Navy (JAN) Military grade tubes which have the lowest noise levels compared to all others. They are durable because they were designed for military use in field/ship radios that went into battle and had to take allot of abuse before they failed. The price is very good considering the fact they aren't made any more. (If they were 12AX7's they'd sell for a couple of hundred each, but because they are usually used as inverters, the demand is much lower) 12AT7's are a slightly lower gain tube which can be used as a preamp as well, but for an inverter they are a more durable choice.

 

It may have some change in gain, but I doubt it. All your gain is coming from solid state circuitry and the power tubes. The inverter simply creates the proper wave polarity for the power tubes.

 

Other then that, all the things you done so far shouldn't have been necessary. Power tubes aren't normally microphonic they cant be because they are the last gain stage. In order for tubes to be microphonic its got to begin earlier in the amplification chain. Bad power tubes can make noise, pop and crackle or hum, the inverter tube, doesn't amplify it changes wave polarities.

 

I've swapped many 12AT7, 12AX7, 12AU7 and 5751 tubes as inverters and never heard any difference in tone or gain. They can produce noise when they get old but that's about it. your amp has no preamp tubes so its unlikely tubes are your problem.

[DeepEnd]

. . . Power tubes aren't normally microphonic they cant be because they are the last gain stage. In order for tubes to be microphonic its got to begin earlier in the amplification chain. . . .

Then I wonder why John Templeton's review of the Tung-Sol 6V6GT for thetubestore.com specifically mentions microphonics?

. . . No microphonics with the Tung-Sol and a very low noise floor. . . .

[WRGKMC]

Many terms in electronics can be used to describe things in several different ways. The terms often came about by non scientific slang to describe things. This is one of them.

 

In his case he was using the term as a noun and a measurable value, not as a verb or an effect in motion.

 

They use term Microphonics as an acoustic measurement to describe whether external noise can disrupt the normal signal operation of the tube.

 

This can be of course a regenerative feedback loop most commonly associated with tubes but it also includes any changes to the signal induced when the tube is being physically vibrated. It can be Feedback, noise, static, distortion, and loss of power as well.

 

IE, a vibrating grid doesn't make a very good target for electrons to pass through. The tiny holes in the screen are a moving so electrons wind up which deflected and fail to reach the plate in a straight path. The moving target essentially makes the grid holes a small portal to get a straight beam so the signal gain of the tube may drop when the tube is vibrating compared to when its stationary. You may not hear this as a microphonic noise but it may be a measurable value in the way it influences the signal.

 

Power tubes can be used as preamplifiers if there were placed in the right circuit, so they could produce microphonics feedback if they were in the right circuit. The likelihood of them ever being used that way is unlikely however. The Microphonic value of the tube may simply be a physical noise disruption of the signal path, not a regenerative loop.

 

The chain has to be regenerative in order to produce microphonics. You have to have at least one additional stage to create reaeration.

 

Here's a normal example of that.

 

Speaker vibration >

Vibrates tube elements enough to influence the signal>

The signal is boosted by the next amplification stage (power tubes) >

This is output to the speakers >

Speakers hit the tube again>

The noise that was amplified is the proper pitch and frequency to make the tube elements vibrate even more intensely and therefore sets up a self sustaining loop>

This loop occurs over and over so long as there is speaker movement.

 

Tubes often stop oscillating when you dampen the guitar strings buy you play the right note at the right pitch it oscillates with the note. I've had tubes where you simply tap it and it will ring and produce bell like tones. They are so sensitive any external vibration sets them off. They may even begin to oscillate with no input signal to set them off. Just walking across a wood floor can do it. Others can be much more difficult to trigger.

 

The key is the noise from the tubes need to be amplified up to a higher level before it will regenerate in a loop.

 

Power tubes being hit by the speakers may make static noise - that's often lumped under the term microphonic simply because the noise stops when you isolate them from the vibration. Its its actually a misuse of the term microphonic because there is no addition gain step to step the noise level up in gain. The speakers are the only thing after the power amp and they consume energy, they don't produce it so they can't gain the noise up in a loop.

[onelife]

@WRGKMC

 

I disagree with your use of terminology. I used to play through a Mesa Boogie Subway Blues that got its sound by torturing a pair of EL84s and, quite often, the EL84s would become microphonic and need to be replaced.

 

What you are describing in your comment (regenerative loop) is feedback as a result of microphonics which would indeed require multiple gain stages.

 

There is still gain in the final stage of a tube amp and if a power tube has components loose enough to vibrate then that vibration will be amplified in the final stage especially if it is the control grid that is loose.

[DeepEnd]

Since you don't even know the difference between a noun and a verb I'm not sure how much credence to give the rest of your ''explanation.'' ''Distortion'' is a noun. ''Clipping'' is a noun. A noun names a person, place, thing, etc. An adjective, not a verb, describes a noun. A tube that is ''microphonic'' (adjective) produces ''microphonics.'' A tube that isn't doesn't. In this case, I suspect one or more of the tubes are picking up vibration from the chassis of the amp, which is why the silicone rings, which damp airborne vibrations, aren't solving the problem, because they're being conducted through the sockets. If I'm wrong, fine, but my ''explanation'' accounts for what the OP is hearing.

[jjang1993]

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[DeepEnd]

^ Good on you. I hope the problem is gone for good. I just hope something in this thread actually helped. For my part, I know now to listen to my gut.

[jjang1993]

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[mrbrown49]

I emailed Fender about the problems with the Groove Tube 6V6Rs last friday with scans of the receipt and a package arrived from them today with a fresh set of 6V6Rs free of charge. The 6V6s I had in them before were a rated at a 6' date=' the ones that arrived today were rated at a 5, so there is a little less headroom. I installed them, rebiased a little cold (35mA instead of 40mA) to get a little more life out of these tubes. The overtone problem is totally gone! I'm going to keep the amp on while I cook and eat dinner later tonight and then check to see if the problem comes back. Really impressed by Fender's customer service this time through.[/quote']

 

Nice!

[WRGKMC]

I disagree with your use of terminology. I used to play through a Mesa Boogie Subway Blues that got its sound by torturing a pair of EL84s and, quite often, the EL84s would become microphonic and need to be replaced. What you are describing in your comment (regenerative loop) is feedback as a result of microphonics which would indeed require multiple gain stages. There is still gain in the final stage of a tube amp and if a power tube has components loose enough to vibrate then that vibration will be amplified in the final stage especially if it is the control grid that is loose.

 

You disagree, then you agree. Maybe I can clarify things with some Google quotes.

 

The term microphonics comes from analogy with a microphone, which is intentionally designed to convert vibrations to electrical signals. Just because I use my own analogies, doesn't change the fact it can be used to describe an active effect or an end result.

 

Microphonics describes the phenomenon where a tube transforms mechanical vibrations into an undesired signal (noise or feedback). Due to the mechanical construction all tubes exhibit some inherent microphonic tendencies. The most critical application regarding microphonic tubes are high gain preamp stages that are close to the input. This is especially true in combo amplifiers where the chassis is mounted in the same cabinet with the speaker. The preamp stage close to the input of the amplifier has more stages after it to amplify the signal plus any noise and microphonics. Most technicians will handpick the first preamp tube for the least noise and microphonics. A tube that is not suitable for the first preamp stage can many times be used in a later preamp stage in the signal chain. As the signal is amplified, the increasing level of the signal will override the microphonic tendencies. Since there are less stages of amplification following these stages the microphonics will be amplified less.

 

The "last" stage isn't going to be regenerative. It can be microphonic. It can sound like it produces bell tones but the last stage cant be regenerative because the next step, the output transformer and speaker consume power. You have to have gain above 1:1 to become regenerative and a speaker is a load not a gain stage. They don't amplify the signal they transduce it.

 

Dual Triode power tubes like a 6SN7 can be run in series and become regenerative but these tubes aren't normally used in musical audio gear. Most power tubes are single plate designs and are the last stage of power amplification. If you use power tubes in in series then the set before the last can regenerate. This amp doesn't use series power tubes. Its a simple push pull.

 

Any noise or any loss of signal strength due to mechanical vibration falls under the category of microphonics. Microphonics is not selectively categorized as being only a bell tone or something that sounds like microphone , but a regenerative loop that's sounds like a microphone is one form of microphonics.

 

Since you don't even know the difference between a noun and a verb I'm not sure how much credence to give the rest of your ''explanation.'' ''Distortion'' is a noun. ''Clipping'' is a noun. A noun names a person, place, thing, etc. An adjective, not a verb, describes a noun. A tube that is ''microphonic'' (adjective) produces ''microphonics.'' A tube that isn't doesn't. In this case, I suspect one or more of the tubes are picking up vibration from the chassis of the amp, which is why the silicone rings, which damp airborne vibrations, aren't solving the problem, because they're being conducted through the sockets. If I'm wrong, fine, but my ''explanation'' accounts for what the OP is hearing.

 

Sir you read but you don't comprehend. Please don't get bogged down in semantics because you will simply fail to understand the broader topic. Having a degree in English is not a requirement for getting a degree in electronics. If it was most of the technicians and engineers would be practicing their trade without a diploma. Its a cheap shot in any case. Again I will attempt to explain.

 

 

 

Microphonics can be one item in a "category" of mechanical or electronic faults, it can be a rating "Noun".

Many manufactures give their tubed a microphonic fault ratings, just like they do for Gain, headroom Frequency response etc.

 

 

 

Microphonics comes from the word Microphony.

 

microphony

 

image: http://cf.ydcdn.net/1.0.1.56/images/...onary-logo.png

Noun

• microphonics (unwanted signal caused by vibrations)
  

 

As you can see by the definition it is a Noun and its described as a signal, not a sound. A signal may or may not produce audible results. The signal may be in the range of hearing or it may not. It can dampen, darken, distort the signal, or it can cause a various array of noises once it is transduced by the speaker, regenerative feedback being one of them.

 

 

Microphonics or microphony describes the phenomenon wherein certain components in electronic devices transform mechanical vibrations into an undesired electrical signal (electrical noise). The term comes from analogy with a microphone, which is intentionally designed to convert vibrations to electrical signals.

 

 

Microphonics can be used as an adjective to describe whats going on. ie " The signal was microphonically contaminated by speaker vibration"

 

It can be a noun when describing the end result

 

microphonics

 

(ˌmaɪkrəˈfɒnɪks) n undesirable noise in an electronic device

 

 

 

The root word can also be used as a verb. ie. The signal noise was miked up in gain.

 

DeepEnd - you know I don't claim to be an English major but I do understand my trade well enough to earn a very good living at it and in my spare time I enjoy helping others by giving them suggestions. I don't post here to compete with you.

 

My pointing out these details are simply to broaden the perspective on the topic so people can widen their focus and not be affixed on the dead end conclusions.

 

Every good tech knows he may have to retrace his steps with a broader scope when simple solutions fail to yield results. Every problem has a solution if you're willing and capable enough to find it.

 

If a narrow view is sufficient for you then simply ignore my expanded descriptions on the topic.

 

Others who fail to find faults may be helped by broadening their view however. I've worked with hundreds if not thousands of techs over the years. Discussing troubleshooting dead ends is common place. I've seen techs completely boxed in convinced the problem cant be solved and their egos wont lent them admit they missed anything.

 

The first thing you have to do to help them is get past the ego and make them realize they are suffering from tunnel vision. Once you do that you can give them a new perspective on the problem by helping them view the issue it from a new angle. As in most troubleshooting the tech is his own worst enemy. he assumes things to be true before he has actually made tests or uses short cuts which are not bullet proof.

 

Simply having the knowledge that someone may not have checked all the possibilities changes a closed mind into an open mind, and then new paths they were never considered before can be open to them. This is not unique to electronics either. It is common is all trades and professions in countries where people compete for a better standard of living.

[DeepEnd]

Let's look at what you actually said:

 

In his case he was using the term as a noun and a measurable value' date=' not as a verb or an effect in motion.[/quote']

An effect is not a verb, it's a noun.

 

Microphonics can be used as an adjective to describe whats going on. ie " The signal was microphonically contaminated by speaker vibration"

In your example, "microphonically" is an adverb. It modifies "was." In any event, you said microphonics was impossible in power tubes. onelife says otherwise. The OP's direct experience says otherwise. If I have to put what you claim up against objective reality I'll choose reality, thanks.

 

. . . The first thing you have to do to help them is get past the ego and make them realize they are suffering from tunnel vision. Once you do that you can give them a new perspective on the problem by helping them view the issue it from a new angle. As in most troubleshooting the tech is his own worst enemy. he assumes things to be true before he has actually made tests or uses short cuts which are not bullet proof.

 

Simply having the knowledge that someone may not have checked all the possibilities changes a closed mind into an open mind, and then new paths they were never considered before can be open to them. . . .

Good advice. Please take it.

[WRGKMC]

Come on now, none of what you posted is useful to anyone.

 

All you're doing is playing Gotcha now. When you resort to Nit picking peoples words apart its a clear indication you have nothing useful to add to the topic and are simply trying anger others. I'm not going to play that game so please Grow up.

[DeepEnd]

Really? None of it? Not even the part where I said you were wrong and backed it up with facts? Constructive criticism should be helpful. It tells the person being criticized that there's an issue and if there are onlookers it also tells them. In this case, it tells you to have that open mind you wrote about and it tells the OP to take your advice with a grain of salt.

Oh, and have you noticed that when monkeys are challenged they fling excrement? I seem to see a lot of excrement coming my way. Maybe we're not as evolved as we'd like to think sometimes.

[gdsmithtx]

Hopefully this set of Groove Tubes can hold up well. I took off the silicon rings as I think they might decrease tube wear by acting as a heat insulator. I wish I had another amp that ran on 6v6s so I could test the ones that had the odd overtones. Perhaps I'll see if I can discretely test them on an amp at GC. I know the Super Champ has tube retainers you'd have to unscrew' date=' not sure about the other 6v6 type amps out there though. [/quote']

 

 

Not specifically related to your rattling issue, but I own that same amp and replacing the "okay" stock speaker with an Eminence Ragin' Cajun really improved the tone for me. A lot.

[jjang1993]

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