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Post subject: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Sun Nov 13, 2011 6:00 pm
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Ok, I kinda want to get to the bottom of this whole "microphonic" tube thing. SOOO.. A so called microphonic tube makes a rattle noise or as I would say a ringing noise. If a noisey tube is considered microphinc and "bad" why is it that my "microphonic" or rattleing tubes still seem to work great and sound great and seem to be very dependable. As long as I turn my amps volume up over the "rattle" noise which dose not come through the speaker btw everything seems fine. SOOO.. why is it that a rattleing tube is bad?


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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Sun Nov 13, 2011 6:31 pm
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A microphonic tube is physically defective. The elements inside are moving due to vibration and they shouldn't. Although a microphonic tube may still sound OK and perform as it should electrically, it will eventually fail. Why wait and have that happen in the middle of a gig or recording session. Replace any tube that is microphonic as soon as you discover it. The time you lose due to a tube failure at an inopportune moment costs more then the price of a new tube. At least keep a few tubes on hand as spares.

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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Sun Nov 13, 2011 7:39 pm
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I agree with Bluesky, if the tube is actually rattling noise or goes into an uncontrolled feedback--- replace it.

But in my experience, all tubes have a certain degree of microphony. But, I believe it's mostly resonance of the glass tube that lead to the ringing tone that you just can't get with solid-state amps. Esp high-gain front end tube (12AX7 and 6SN7). It's why you can induce feedback just by moving a ringing guitar near the amp. Very cool, indeed. As long as you can stop the feedback by dampening the strings or backing off the volume.

I abhor tube rings (Herbies, etc)-- because they tend to deaden the live quality of the amp. They work on tube going loosey-goosey. But, only for awhile. Eventually, that tube's gut will go bad and need replacement.

One of the more ingenious methods of isolating the tubes from external vibrations is to place in on a dampener adapter, that then fits onto the chassis. They ring the socket and isolate the tube and usually are vented to help heat dissipation.


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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Sun Nov 13, 2011 11:02 pm
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A microphonic tube, or even a rattling tube, might work OK depending on it's position in an amp (V1, V2, etc). Some positions amplify the tubes sensitivity more than other positions. If a tube howls/rings in V1, it might sound OK when used in V2 for example. These tubes can still work fine for years (if you can tolerate the noise, I couldn't), or as mentioned, they could fail at an inopportune time. Rattles can sometimes be subdued by tube dampers, or playing loud enough to cover up the rattle noise. Microphonic tubes however, can still howl even when dampers are used, and turning up the volume only makes them worse.

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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Mon Nov 14, 2011 12:52 am
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My power tubes make the ringing noise but, I have not heard the squeal other than normal feedback that I can control with my guitars volume. These tubes I have are interresting cause they dont rattle or ring at low volumes but, more at a middle of the road volume. Basically if I have my amps volume set at 1-2.5 I get no noise then at about 3-3.5 they start to get noisey then at 3.5 and above I cant hear it really at all over the sound actually comeing out the speaker. I think im going to order some new tubes. Wish I knew the "hardness" rateing on these dang tubes so I could just order some new ones and put them in without rebias. BTW, my amps a SS22 with JJ6v6s power tubes. I started this new thread cause I didnt want to jack the other dudes thread but, I guess this thread is pretty much the same thing haha! Sorry... Hmmmm... actually, since my amp has been biased for the JJ6v6s tubes and my amp dose seem to be performing very well and the .com store im wanting to order the tubes from says to specify the amp that the tubes are going to be used in when you order shouldnt I be ok just ordering a new matched pair of the JJ6v6 tubes?


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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Mon Nov 14, 2011 7:00 am
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jason1978 wrote:
Hmmmm... actually, since my amp has been biased for the JJ6v6s tubes and my amp dose seem to be performing very well and the .com store im wanting to order the tubes from says to specify the amp that the tubes are going to be used in when you order shouldnt I be ok just ordering a new matched pair of the JJ6v6 tubes?


In my opinion, you should always check bias whenever you replace tubes, regardless of the color code, matching, etc. Component values drift with time and temperature, power line voltages change depending on the season or even the time of day. Tube specs are "nominal" and can vary from tube to tube, that's why they are "matched". If you learn how to safely check/set the bias yourself, it is a fairly quick and simple procedure, well worth the piece of mind it will give you. :wink:

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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Mon Nov 14, 2011 9:00 am
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+1 bluesky636

jason1978,

In order to get the same performance from the new JJ tubes (or any brand), you would need to know their rating number(s) as supplied by the vendor that matched them, and order the same rated tubes from the same vendor. Most vendors have their own rating system when matching tubes, and one vendor's system may not translate to the same numbers of another vendors system. So, odds are, if you don't get the exact same rated tube, the bias likely needs to be checked and/or adjusted. In my experience, the GTs are right on the money with the bias being the same for the replacement tubes, but I still check the bias anyway just to be certain, no matter what tubes I put in.

It is easy to get exact replacements for GTs, as the rating is derived from the same system no matter where you buy them. With other brands of tubes, you rely on the vendor to rate them, so in order to get the exact same tube, you should use the same vendor and the same number rating that they provide. For example thetubestore.com and tubesandmore.com (AES) both have different rating systems for their tubes, so a 27 rating for thetubestore may not necessarily correlate to a 27 from tubesandmore (AES uses two numbers for their tubes). :idea:

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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Mon Nov 14, 2011 1:24 pm
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I see, I believe that the best thing for me to do is to learn how to do the bias myself on my SS22. There are several shops where I live but, the one shop that did my tube change and bias gave me the ringing tubes to start with I asked them if they could give me a contact number of the guy who dose the amp work and they wouldnt give me a number and also said he dosent keep track of the grades of the tubes Btw, the amp guy dosent work at the shop but, comes on mondays to pick up the amps to be repaired and brings them back on thursday. Soo as you could guess I really aint wantin to deal with them any longer. I havent talked to any of the other shops yet... In the long run its just better if I learn how to do it myself.


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Post subject: Re: Is a microphonic tube actually a bad tube? Not trolling!
Posted: Mon Nov 14, 2011 2:19 pm
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jason1978 wrote:
In the long run its just better if I learn how to do it myself.


Buy this

http://www.amp-head.com/product_info.ph ... ucts_id=70

and a decent digital voltmeter and you are all set to safely measure both the cathode current and plate voltage which will allow you to calculate the % of maximum plate dissipation of the power tubes based on the bias setting.

The bias adjustment pot is R156 as shown on page 2, domestic power supply schematic.

http://support.fender.com/schematics/gu ... ematic.pdf

Adjust the bias pot until the product of the cathode current and plate voltage as measured by the bias probe is about 50% to 70% of the maximum plate power dissipation of the tubes you are using. If you switch to JJ 6V6S, they are rated at a maximum of 14 watts, so you want to set them so that the bias setting gives you a value of anywhere between 7 and 9.8 watts per tube. The bias probe comes with detailed instructions which makes it easy to use.

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