tubes age 54
<< You may be thinking of the 7025, which is a low hum version of the
12AX7,...................
According to the book " Tube Lore ", the 12AU7A is a low microphonic 12AU7.
IMPROVED VERSIONS OF TUBES "An A or B version of a tube is improved
over the basic model and will replace it ( except for some Wester Electric tubes
which are incompatible from " A " to " B " ). However, many " A " versions of the
mid-'50's are improved ONLY in that they warm up in a controlled length of time.
This is important in series-string TV sets but meaningless in parallel-wired
equipment. Improvementss in other types may or maay not matter, depending
on the use: 6AF4A is simply shortened physically; the 12AU7A is a low
microphonic type; the 12AX7A is a low noise, low hum variant.
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Date: Sat, 16 Dec 2000 07:54:35 +0000
Subject: Re: [R-390] 12AU7 and 12AU7A tubes
HSN has a bit about the order of desirability for the 12AU7 and 12AX7. I forget
the details at the moment. I know the 12AX7 is pretty expensive nowadays.
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Date: Sat, 16 Dec 2000 10:52:47 -0600
Subject: Re: [R-390] 12AU7 and 12AU7A tubes
>You may be thinking of the 7025, which is a low hum version of the 12AX7,
>most commonly used in guitar amplifiers.
No, I've got a couple of 7025's around here somewhere and know about them.
It was something to do with the "A" version for one of the 12A_7 types if
signified a low hum version. I'll head inside in a bit and dig out the tube
manuals and dig a bit. My curiosity is aroused now. <grin>
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Date: Sat, 16 Dec 2000 12:59:55 -0500
Subject: RE: [R-390] 12AU7 and 12AU7A tubes
Here's the listing of 12AU7 types I posted to the reflector back in Sept. The
12AU7A is an exception to the usual "low hum" rule for the "A" suffix. In this
case it was for low microphonics. Western Electric also was famous for having
"A" versions that were entirely different tubes - for example the 350A is an 807
like tube, the 350B is a 6L6G type, the 274A is a 4 pin 5Z3 like rectifier, the
274B is an octal base rectifier etc. (see earlier post for this list)
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Date: Sat, 16 Dec 2000 12:38:22 -0600
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