[Harp-L] Shure Hi/Lo Impedance xformer on eBaY

["Splash" <celtiac@xxxxxxxxx>]

eBaY item number

160254140947

Thought someone on here could use one of these.  The question comes up
frequently.


PEACE
Scott
Believe in Magic!
----- Original Message -----
From: "Frank Evers" <frank@xxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Saturday, June 28, 2008 8:31 AM
Subject: Re: [Harp-L] 12AX7 vs 12AU7 power requirements


> Hi
>
> Am Samstag, 28. Juni 2008 schrieb gary:
> > I read on the list where someone said that a 12AU7 will draw more
> > power than a 12AX7 and that the extra power draw could damage some
> > cheaper equipment. What about a 12AT7 and a 12AY7 do they draw more
> > power than a 12AX7?
>
> It was probably me who brought this up. The 12AU7 actually draws more
> current. This current doesn't only run throught the tube itself, but
> also through a few resistors. These resistors heat up. They always
> do, but the more current runs through them, the more heat they have
> to take.
> Usually an engineer will opt for a resitor, that can take at least (!)
> four times the heat thats expected to happen in normal operation mode
> just to provide an extra secutity bonus in case of shortages, etc.
>
> With a 12AU7 when the circuit design is designed to hold a 12AX7 this
> bonus is probably not enough.
> Scott is right, vintage point to point wired amps are usually built
> very failsafe, and you won't have to worry about breaking anyting
> while using a 12AU7. However today amps are build in a very
> competitive economical environment and manufacturers have to build
> their products at low costs. So the rule of thumb should be not to
> replace a 12AX7 with a 12AU7 in these amps.
>
> Using an AT or AY should be ok though. Even if they draw more current
> than the AX things should still be within specs.
>
> --
> Gruß,Frank
>
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