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Big Road Blues Discussion Forums 2006-04-13T20:43:53+00:00 http://www.bigroadblues.com/forum/feed.php?f=7&t=814 2006-04-13T20:43:53+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8088#p8088 <![CDATA[RE: Tube-ular, man]]>
Lots of high gain tube amps are built with preamp stages set up for pretty high gain, but dump most of the output voltage in resistance networks between stages. A typical 12AX7 stage can only take up a bit more than 1V peak to peak on the input before it begins to clip, but will put out something like 43-66V. That's why a simple amp like the Valve Junior with two 12AX7 stages (in a single tube) can overdrive so much. A P90 or really hot humbucker can just hit 1V at the beginning of a hard picked or strummed note, and momentarily just about saturate the first stage. A Fender single coil won't come close. Maybe an eighth of that voltage. But every subsequent stage can get overdriven hard if some gain's not dumped.

"A cheerful heart is good medicine."

Statistics: Posted by ricochet — Thu Apr 13, 2006 8:43 pm


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2006-04-13T17:17:04+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8087#p8087 <![CDATA[RE: Tube-ular, man]]> >plate current.

It's unfortunately all Greek to me. He probably said 'plate current' too; my knowledge of electronics is limited to pretty simple circuits (i.e. without transistors).


>It's unlikely to cause a problem, though, as
>12AX7 guitar amps pretty much always have at least a 100K
>ohm plate resistor and 1.5k cathode resistor, which is going
>to keep the plate current low enough to not burn anything up
>with a 12AY7.

I'll poke around the board some more and look for big resistors. I was aware that people swap in lower gain tubes (or wouldn't have had the idea in the first place), but I've not read about people trying it in hybrid amps, and am not sure how that changes anything.

Statistics: Posted by rustyslide — Thu Apr 13, 2006 5:17 pm


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2006-04-13T14:18:07+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8086#p8086 <![CDATA[RE: Tube-ular, man]]>
"A cheerful heart is good medicine."

Statistics: Posted by ricochet — Thu Apr 13, 2006 2:18 pm


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2006-04-13T13:29:17+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8085#p8085 <![CDATA[RE: Tube-ular, man]]>
I was talking with my dad (electrical engine-gear), and he was concerned that there would be too much grid current coming out of the 12AY7 for the amp if it was designed for a 12AX7, and that would potentially cause problems.

Statistics: Posted by rustyslide — Thu Apr 13, 2006 1:29 pm


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2006-04-11T16:25:24+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8084#p8084 <![CDATA[RE: Tube-ular, man]]>
"A cheerful heart is good medicine."

Statistics: Posted by ricochet — Tue Apr 11, 2006 4:25 pm


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2006-04-11T04:51:08+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8083#p8083 <![CDATA[RE: Tube-ular, man]]>
I tried one of the 12AY7s tonight - worked like a charm. Gain channel is a lot more subtle now (it used to get 'crunchy' pretty quick).

Found this page and thought it was interesting:
http://home.comcast.net/~machrone/bjr/bjtubes.htm

Statistics: Posted by rustyslide — Tue Apr 11, 2006 4:51 am


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2006-04-10T18:32:31+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8082#p8082 <![CDATA[RE: Tube-ular, man]]>
"A cheerful heart is good medicine."

Statistics: Posted by ricochet — Mon Apr 10, 2006 6:32 pm


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2006-04-10T18:32:03+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8081#p8081 <![CDATA[RE: Tube-ular, man]]>
"A cheerful heart is good medicine."

Statistics: Posted by ricochet — Mon Apr 10, 2006 6:32 pm


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2006-04-10T17:47:41+00:00 http://www.bigroadblues.com/forum/viewtopic.php?t=814&p=8080#p8080 <![CDATA[Tube-ular, man]]>
I snagged 1 12AX7 (Siemans), 2 12AY7s (RCA-Electra), and 1 12AT7 (dunno the brand, the writing's worn off - was in the 12AT7 slot in the chassis though). I've heard that 12AY7s are lower gain than AX7s, and I seem to recall the AT7 as a rectum-fryer tube. But other than that am pretty clueless.

Anything I should know before swapping tubes (unplug it!) ?

I don't think I have to do any biasing with one tube, do I? the manual certainly doesn't mention it.

Statistics: Posted by rustyslide — Mon Apr 10, 2006 5:47 pm


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