audiophoolery?
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Echo North
Well-known member
$16 - $40 a pop!
Interestingly enough I'm about to start selling tube neckties. They do nothing for your sound but your tubes will look a lot more professional.
Mike
Interestingly enough I'm about to start selling tube neckties. They do nothing for your sound but your tubes will look a lot more professional.
Mike
Plink a tube with your finger while you hold it next to your ear.
There's a LOT of mechanical resonance in there.
The effect on a tube alone in a room is unclear. But tubes NEXT to speakers (any guitar "combo amp") can have violent mechanical feedback.
There's a LOT of mechanical resonance in there.
The effect on a tube alone in a room is unclear. But tubes NEXT to speakers (any guitar "combo amp") can have violent mechanical feedback.
Svart
Well-known member
So the issue is: can external sound waves vibrate the innards of the tube through the glass portion enough to cause problems? Sure, physically hitting the tubes makes them ring but since the active portions are in a vacuum, the vibration comes from the base vibrating up through the stalk area. I just don't see how putting a lightweight damper on the glass can stop a guitar cabinet from vibrating the active parts. It may help keep the glass from vibrating sympathetically from a loud source in the room but won't help otherwise.
You'd need to completely isolate the tube from all mechanical forces and then use the most flexible wire possible to keep vibration from getting into the tube.
Not an easy task but certainly do-able.
You'd need to completely isolate the tube from all mechanical forces and then use the most flexible wire possible to keep vibration from getting into the tube.
Not an easy task but certainly do-able.
Winston OBoogie
Well-known member
If it works, it's not 'phoolery in my opinion.
I once reworked a commercial pre amp for a company. Most of the stuff I did for the job involved a re-layout out of the PCB and adding a couple of features. But one of the issues with the older version was that certain input tubes were slightly microphonic. This was only really evident when you flicked a switch on the front panel since the switches were, by necessity, on the same PCB as the tubes. A "ping" was heard through the channel if you flipped polarity or engaged Pads etc.
I tried tube dampers and they did work but, since I was re-doing the PCB anyway, I was able to do it a bit cheaper by putting the input tube on a small daughter board which had short, flexible leads to the main board. The board could be isolated with a couple of soft rubber grommets (an old trick) or, as the company opted to do, use some small, double sticky foam strips.
Other times I've had to use both an isolated daughter board (or socket) and some dampers. Some of the very early ('30's) and later '40's tubes are great sounding - very linear - but are quite microphonic. Since some are also quite hard to come by, swapping them out can be an expensive issue, so I do what I can to get the vibrations down.
Other times, the tubes are so cheap that I just sort them and trash the "pingers".
Y.M.M.V.
I once reworked a commercial pre amp for a company. Most of the stuff I did for the job involved a re-layout out of the PCB and adding a couple of features. But one of the issues with the older version was that certain input tubes were slightly microphonic. This was only really evident when you flicked a switch on the front panel since the switches were, by necessity, on the same PCB as the tubes. A "ping" was heard through the channel if you flipped polarity or engaged Pads etc.
I tried tube dampers and they did work but, since I was re-doing the PCB anyway, I was able to do it a bit cheaper by putting the input tube on a small daughter board which had short, flexible leads to the main board. The board could be isolated with a couple of soft rubber grommets (an old trick) or, as the company opted to do, use some small, double sticky foam strips.
Other times I've had to use both an isolated daughter board (or socket) and some dampers. Some of the very early ('30's) and later '40's tubes are great sounding - very linear - but are quite microphonic. Since some are also quite hard to come by, swapping them out can be an expensive issue, so I do what I can to get the vibrations down.
Other times, the tubes are so cheap that I just sort them and trash the "pingers".
Y.M.M.V.
Svart
Well-known member
Ford did a trick in the 80's where the rear ends of their mustangs would vibrate and you could hit a speed that would cause an oscillation that felt like the thing was coming apart..
They took a weight, added rubber grommets and attached it to the rear end. It worked like a champ.
I could see making very heavy rings to attach to the tubes but not these little tiny things that this company is selling. You want your weight to be heavy enough to waste all of the acoustic energy that is trying to move it. the other thing is that you want to attach it to the tube with some kind of material that is limp enough to give freely but also rigid enough to keep the weight from pulling itself off of the tube.
They took a weight, added rubber grommets and attached it to the rear end. It worked like a champ.
I could see making very heavy rings to attach to the tubes but not these little tiny things that this company is selling. You want your weight to be heavy enough to waste all of the acoustic energy that is trying to move it. the other thing is that you want to attach it to the tube with some kind of material that is limp enough to give freely but also rigid enough to keep the weight from pulling itself off of the tube.
Junction
Well-known member
As mentioned by PRR, it is quite common to experience feedback problems in an EF86 combo guitar amp design, I use one or even two tube rings on the EF86 to tame it. With lower gain tubes the problems in a combo guitar amp are almost negligble or not noticeable.
One might think that a tube mic pre-amp could suffer feedback in a studio where you run high control room monitor levels or have a sub-woofer in close proximity.
Would be an interesting experiment, run tone thru a mic pre-amp, measure the amplitude and/or distortion and then run music with lots of bottom end thru some monitors in close proximity and see if there is any affect on the pre-amp output. My studio is in pieces at the moments so cannot do this test for a few months.
Michael
One might think that a tube mic pre-amp could suffer feedback in a studio where you run high control room monitor levels or have a sub-woofer in close proximity.
Would be an interesting experiment, run tone thru a mic pre-amp, measure the amplitude and/or distortion and then run music with lots of bottom end thru some monitors in close proximity and see if there is any affect on the pre-amp output. My studio is in pieces at the moments so cannot do this test for a few months.
Michael
Junction said:
I'm experiencing this with a recent EF86 guitar amp build, even after mounting sockets using rubber grommets between socket and bolt, as well as between socket and chassis. Don't know if they still do, but Dr Z amps used to ship their EF86 amps with thick heat-shrink on the EF86. My attempts at using EF80 have been even more fraught with oscillation, despite having ~70 to choose from.
Not audiophoolery, a pain in the butt!
Winston OBoogie
Well-known member
Junction said:
The commercial mic amp I mentioned used an EF86 as input stage. As I said, the problem was not major and did go away with a couple of damper rings. I suppose if the dissipation is not too much, you could try 'O' rings as a cheap alternative? Never have myself. Don't know how long they'd last but maybe you could condition them with pinch roller fluid? I've also jammed some neoprene strips inside a shield which seemed to help that time.
Svart is right that weight would help. I've also done something similar to what was done inside a V76. The input transformer and input tube were mounted on a separate little metal plate that had extra weight attached and was isolated from the main board with shock mount stand offs.
As it happens, 3 days ago, I picked up some N.O.S. surplus jobbies that are 1949 vintage and made by a Robinson Aviation Inc. called "MET-L-FLEX Vibrashock Products".
They look like they'd be great for isolating a large internal chassis. Each one can handle up to 1 3/4 lbs so one in each corner might be groovy...
> Ford did a trick in the 80's where the rear ends of their mustangs would vibrate and you could hit a speed that would cause an oscillation that felt like the thing was coming apart..
Not quite.
Sit in the back of a Chevy Nova for a day-trip to DC. You don't notice, but there is a booming noise from the trunk which gives you a headache.
Somehow Ford noticed this on the essentially similar Falcon. Cost, weight, was totally out of the question. Instead they lightened the rear "frame" rails to shift the resonance. I suspect the Nova had "frame"/floor resonance amplified by trunk air-volume resonance; the Falcon/Mustang metal thunked a higher pitch than trunk volume boom.
The Cougar went further, with 200 pounds of clay/tar mats under the back seat.
The flip-side of lightening the "rails" is that after a couple decades of rust, you can put your finger through the rear "frame" rails.
The Accord does have a rubber-wrapped lump on the front frame, damps a something or other vibration. And one of the engine mounts is hollow with an electric valve: traps the air, or not, under ECU control. I have not figured out if this is supposed to tame the idle-shake, or let the engine float free at high RPM and light load, or what.
> I just don't see how putting a lightweight damper on the glass
Touch a finger to a working tube. Very light touch can make a real difference. I see what you are saying, you want to GRAB that tube with an 800 pound gorilla. But much lesser dampers can have real effect.
Remember are not getting much vibration "through" the glass. The whole bottle is poorly supported on 9 sorta-tight socket holes, and shakes easily. The "shields" often used on older gear can be electric field shields, but they often suppress bottle vibration too. Rather, some do and some don't.
As Charlie says: "damper rings" are three for a dollar at McM-Carr or the NAPA parts store. Most NAPA have a tray of O-rings, rated for engine heat. Any of these will be cool on 12AX7; a full-heat 6550 may toast the general-purpose Neoprene but there are Silicones which stand up to more than a tube seal can take. You wanna know OD and thickness, which will mean some reverse calculation from tube diameter. If they like your look, they will probably let you play with your tube to find a fit you like.
Not quite.
Sit in the back of a Chevy Nova for a day-trip to DC. You don't notice, but there is a booming noise from the trunk which gives you a headache.
Somehow Ford noticed this on the essentially similar Falcon. Cost, weight, was totally out of the question. Instead they lightened the rear "frame" rails to shift the resonance. I suspect the Nova had "frame"/floor resonance amplified by trunk air-volume resonance; the Falcon/Mustang metal thunked a higher pitch than trunk volume boom.
The Cougar went further, with 200 pounds of clay/tar mats under the back seat.
The flip-side of lightening the "rails" is that after a couple decades of rust, you can put your finger through the rear "frame" rails.
The Accord does have a rubber-wrapped lump on the front frame, damps a something or other vibration. And one of the engine mounts is hollow with an electric valve: traps the air, or not, under ECU control. I have not figured out if this is supposed to tame the idle-shake, or let the engine float free at high RPM and light load, or what.
> I just don't see how putting a lightweight damper on the glass
Touch a finger to a working tube. Very light touch can make a real difference. I see what you are saying, you want to GRAB that tube with an 800 pound gorilla. But much lesser dampers can have real effect.
Remember are not getting much vibration "through" the glass. The whole bottle is poorly supported on 9 sorta-tight socket holes, and shakes easily. The "shields" often used on older gear can be electric field shields, but they often suppress bottle vibration too. Rather, some do and some don't.
As Charlie says: "damper rings" are three for a dollar at McM-Carr or the NAPA parts store. Most NAPA have a tray of O-rings, rated for engine heat. Any of these will be cool on 12AX7; a full-heat 6550 may toast the general-purpose Neoprene but there are Silicones which stand up to more than a tube seal can take. You wanna know OD and thickness, which will mean some reverse calculation from tube diameter. If they like your look, they will probably let you play with your tube to find a fit you like.
Winston OBoogie
Well-known member
Gus said:
Thanks Gus. Have done similar many times;
Winston OBoogie
Well-known member
tv said:
I frequently peel back the first layer of a coupling cap and razor it off, but that's sometimes because i don't want someone knowing my brand or value without removing the cap
Usually though, it's only because I need more space to write absolute value in sharpie for matching etc.Maybe I'm a paranoid or obsessive phool? 8)
Svart
Well-known member
there used to be some guy that would remove the metal cover of a cap and then stuff the foil/electrolyte into a wooden case and seal it with beeswax. Something to do with making it sound better.. at like 50$ a pop.
Now that's audiophoolery!
Now that's audiophoolery!
Winston OBoogie
Well-known member
Svart said:
Not if you do it yourself and buy in bulk
I saw that web page once. Where is/was it, do you know?
Cheers.
Junction
Well-known member
[/quote]
I'm experiencing this with a recent EF86 guitar amp build, even after mounting sockets using rubber grommets between socket and bolt, as well as between socket and chassis. Don't know if they still do, but Dr Z amps used to ship their EF86 amps with thick heat-shrink on the EF86. My attempts at using EF80 have been even more fraught with oscillation, despite having ~70 to choose from.
[/quote]
A lot of EF86 tubes appear to be quite microphonic, if you have tested 70 tubes then maybe that is not your problem here. Do you have a shield under the open side of the chassis. It is common practice to use some thin aluminium sheet about the same size as the open side of the chassis (the under side) and staple the sheet to the cabinet, this should clear up or reduce oscillation at high volumes .... EF86 guitar amp designs are regularly problematic with microphonics, oscillation at high volume, good luck.
Michael
I'm experiencing this with a recent EF86 guitar amp build, even after mounting sockets using rubber grommets between socket and bolt, as well as between socket and chassis. Don't know if they still do, but Dr Z amps used to ship their EF86 amps with thick heat-shrink on the EF86. My attempts at using EF80 have been even more fraught with oscillation, despite having ~70 to choose from.
[/quote]
A lot of EF86 tubes appear to be quite microphonic, if you have tested 70 tubes then maybe that is not your problem here. Do you have a shield under the open side of the chassis. It is common practice to use some thin aluminium sheet about the same size as the open side of the chassis (the under side) and staple the sheet to the cabinet, this should clear up or reduce oscillation at high volumes .... EF86 guitar amp designs are regularly problematic with microphonics, oscillation at high volume, good luck.
Michael
Thanks for the tip Michael, this amp is only a test-bed for learning/experimenting and as such is just a chassis on my bench. I will try your suggestion. The group of 70 tubes are Valvo EF80, and I've only gone through 20 or so. It would be safe to assume poor design and lead dress on my part are more at fault than poor tubes
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