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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 11:36 am
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My experience with all different type of tube dampeners is they really only work on certain types of microphonic tubes. Most tubes that ring are due to the GUTS of the tube and NOT the tube's glass envelope. So tube dampeners hanging on the glass may help a bit of the internal resonance, but at high volumes the unwanted noise eventually comes back. Rubber type dampeners are known to muck-up the glass after a period of use. Not good.

All tubes "sing & ring" to a certain degree (internal & glass resonance). You'll find that putting tube dampeners on may change the tonal response of the amp. Esp sustain and high frequency harmonics. Best to avoid dampeners, if possible (IMHO).

As for speaker induced microphony, prolly why there are few 50+ watt combo amps around. Go to separate cabs for more volume. And dampener FEET between the amp and the cab. I've used these prodacts with pretty good success:

http://www.vibrationmounts.com/


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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 4:49 pm
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I have some 6V6 military tubes from 1946 that work great in my DRs,they're RCA and marked VT something or another, I would have to look.
I wish I could come across some 6L6GCs that the military disposed of.
After reading some of the posts about tubes vibrating in some combo amps,I can see why some people try dampening rings,I've just never had a Fender amp with a problem like that.


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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 6:17 pm
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VT-107A = 6V6GT, military use
VT-107B = 6V6G (coke bottle), mil use.

AFAIK, there are no mil spec 6L6GC. The only 6L6GC-type mil spec tube is the Sylvania/Philips ECG 7581A which has higher output. There also is the Sylvania pink ceramic based STR-415 (later versions had black plastic bases) made specifically for Mesa-Boogie in the 1970's. These were made to take higher plate voltages and had stricter noise/rugged specifications.

The TungSol 5881 is a mil spec version of the 6L6GB. Also known as 6L6WGB. Brown based as tough as nails. If you wanna use a 5881, must re-bias amp to 5881/6L6WGB settings.

http://images.cloud.worthpoint.com/wpim ... 916dfa.jpg


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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 10:25 pm
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BMW2002Ti wrote:
AFAIK, there are no mil spec 6L6GC.


Really......?

So WTF do you think these are?

Image

Arjay

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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 10:50 pm
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Arjay,

They are 6L6WGB. Please note my ditty on the 5881/6L6WGB. Tungsol made the first set for the military. Sylvania, GE, and others (including Philips ECG) followed.

Have a cool weekend!


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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 11:12 pm
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I worked with military electronics 24/7/365 for nineteen and a half years. Another eight as a contractor. And I've had my FCC 1st with a radar endorsement since 1977. According to every military T.O., T.M., or F.M. that deals with vacuum-tube equipment, the 6L6WGB is the functional equivalent of a 6L6GC EXCEPT that the critical elements within the bottle are ruggedized for severe use and there is an extra adhesive bead between the base and the glass envelope on the inside to reinforce the vacuum seal. Sonically, I discern no significant difference in tone between a mil-spec 6L6WGB and a commercial RCA blackplate 6L6GC at least in blackface and silverface platforms. Tweeds however seem to prefer the brown Bakelite base 5881s, as do some brownfaces.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 11:40 pm
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Arjay,

I don't doubt what military specifications for this tube was. But, I've used 5881/6L6WGB quite a bit & have followed manufacturer's data sheets with pretty good success. I don't think this tube should be run at the plate voltages that some Fender amps put onto their OEM 6L6GC (425-475 VDC). Maybe, if you run the screen voltage at a conservative value or use a voltage regulated circuit on it, the 6L6WGB could take the plate voltages, just a WAG.

Anyhow, here's Tungsol data sheet:

http://www.mif.pg.gda.pl/homepages/frank/sheets/087/6/6L6WGB.pdf


And a blurb on Tube World's site:

5881 SPECIFICATIONS:
Vh - Ih - VaMax - Vg2Max - PaMax - Pg2Max
6.3 - 0.9 - 360 - 270 - 23.0 - 3.0


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Post subject: Re: microphonic tube?
Posted: Fri Jan 21, 2011 11:54 pm
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If those "some Fender amps" you refer to are the "ultra-linears", I'd agree. Those 70- and 135-watt output stages can be brutal on tubes. Only the hardiest of 6L6's should be used in them. My '78 Twin Reverb was delivered with Fender-branded Westinghouse glass so that's what I've stuck with since it was new (the amp's currently on its second set of tubes -- the first bottles lasted some 23 years).

Arjay

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Post subject: Re: microphonic tube?
Posted: Sat Jan 22, 2011 7:34 am
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I use the 6L6WGB just like those pictured in my '66 Pro Reverb...you think they shouldn't be used at 425/475 VDC?... :?
this is not where I got mine but read the description
http://thetubestore.com/jan6l.html


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Post subject: Re: microphonic tube?
Posted: Sat Jan 22, 2011 12:05 pm
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To be honest, I haven't used the 1980-1990 made Philips ECG 6L6WGB. Only the 1950-60's Tungsol 5881/6L6WGB. I run them at 23-25 watts of dissipation per tube. If you can run your ECG's at 30 watts with no problems, then all is fine. Personally, I wouldn't put a 5881/6L6WGB into an amp that is pushing the anode above 450 volts. With today's outlets often being much closer to 120VAC than the outlet voltages of the 1950-60's... circuits that were rated at 450-475VDC on the plate maybe closer to 500VDC. If you wanna play your amps above "5" for any length of time, I'd use a good 6L6GC. For more power a 7581A or re-pin to use a 7027A. Or the STR-415.

As far as I know, the 5881/6L6WGB was designed to be rugged and take high-G's in Air Force equipment. Gold plated carbonized grids and non-contaminating cathode to take higher current, thus uprated to 23 watts over 6L6GA's 19 watts. But, not neccessarily high plate voltages.

There are a couple of nice articles on the history & usage of the 6L6-type tubes in Issues #4 and 13 of Vacuum Tube Valley. FWIW.

http://www.vacuumtube.com/vtv.htm##12


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