[sdiy] Space Expander 7247 substitute

[anthony]

>> 12AX7's and 12AU7's and some 12AT7's. I thought I'd start with the AU and
>> then the AT. I doubt the AX would work as well and I've heard of people
>> I have a bunch of other twin triodes liek 6BQ7's etc. too.
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> My handy tube substitution book (!) shows 12DW7 to be a good one to 
> replace
> that one with.

That's kind of a tough one to find too innit?. Actually, since I have so 
many different twin triodes I hoped /something/ I already had would work 
which is why I mentioned those examples.

> Regarding that other stuff,  they're not the same in spite of having 
> similar
> pinouts.  I know off the top of my head that 12AX7 is a "hi-mu" triode 
> while
> the 12AT7 and 12AU7 are "medium-mu" triodes,  having a lot less gain.  I'd

I figured I could maybe get it to work with less gain and use the 12AU7 
because that's probably driving the spring.
I'm not above adding a socket and using two tubes either really.

> need to find a tube manual to get other differences.  There were some 
> other
> ones in that series,  too,  all the way out to 12AZ7 but they were a whole
> lot less common.
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