[sdiy] Space Expander 7247 substitute

[Bob Weigel]

I seem to recall having some 7247's if someone needs.  I missed the 
start of this thread. -Bob

anthony wrote:

>>> 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.
>>
>>
>> My handy tube substitution book (!) shows 12DW7 to be a good one to 
>> replace
>> that one with.
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> 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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