Octal equivalent of 12AX7
Chris M
"Luis de Freitas" <ldefr...@netcabo.pt> wrote in message
news:1028878155.389622@spynews4...
> Hello ,
> I'm looking for octal "versions" of the
> 12AX7 and 12BH7........
> Any sugestions ?
> Thanks in advance
> Luis de Freitas
Hi Lou...
The 6SL7 is mu of 70.......
The closest "octal" for the 12AX7 is the 6SF5/12SF5 .... The only problem is
that it is a single triode not dual triode valve....
It is the closest in gm, mu , Rp .....
The second closest octal valve...would be the 6SQ7/12SQ7
Regards
Chris
Luis de Freitas
Thanks everybody for the suggestions .........! !
The reason for this equivalency search is that
I'm building a clone of the famous Teletronix LA-2A
opto-compressor and I would like to replace the
12AX7 and 12BH7 indicated in the circuit by
something more robust and less prone to
microphonics...........
On top of that I have had very good experiences
with some NOS 6SN7 in a mic pre I have build previously.......
Any comments on this ??
Luis de Freitas
"Luis de Freitas" <ldefr...@netcabo.pt> wrote in message
news:1028878155.389622@spynews4...
> Hello ,
>
> I'm looking for octal "versions" of the
> 12AX7 and 12BH7........
>
> Any sugestions ??
Peter Völpel
Further advantages:
low hum when ac heated, 15µV instead 200µV with 12AX7
less crosstalk between the 2 triode-systems
Peter
Luis de Freitas :
Patrick Turner
Luis de Freitas wrote:
The robustness of the 9 pin mini tubes
would be as good as any others for small signal use.
If you need high gain, in place of a 12AX7,
then probably the 6SL7 is the best octal,
which will give the gain required.
To avoid microphonics though,
one should pick through the tubes,
and select for the least noisy, and least microphonic.
Audiophiles do this, and also select for the most
musical sounding tube.
In you case you want to compress music,
so musicality won't be the issue.
Maybe use a guitar amp tube,
which tend to be less microphonic.
In the old days though, a common practice in
tape decks and high gain microphone amps
was to mount the tube socket on small plate on pliable rubber
grommets,
so the socket is slightly above the chassis, and isolated from the
chassis, and using
flexible cabling from the socket lugs to the nearby
lugs to which components, such as coupling caps and
plate and cathode resistances are connected.
The cabling sould only be an inch long,
and be like that used for the leads from lugs to speaker cone
voice coils.
Careful placement will prevent shorts, and perhaps some
flexible silicon tubing over such leads will assist.
If the gear you have is heavy, and has a foam plastic
pad glued to its underside, then vibrations from a bench
it sits on should be attenuated.
Patrick Turner.
Mikkel C. Simonsen
>
> The ECC808 is very low on microphonics, about a third of the 12AX7.
> Further advantages:
> low hum when ac heated, 15µV instead 200µV with 12AX7
> less crosstalk between the 2 triode-systems
But where can you get ECC808s, and what do they cost?
The only place I have ever seen any, is in my Valvo Taschenbuch...
Best regards,
Mikkel C. Simonsen
David Thatcher
I really don't know if the octals are more robust or that the weight
tends to lessen the harmonics in a circuit. Before I started changing
things what I would do is to try and find a low harmonics 12AY7 as a
drop in for the 12AX7 and use a good tube shield. The gain is higher
so you don't have to push it as hard, lots do have low microphonics
and a tube shield will help even more. Then you won't have to perform
surgury on something. I do love my RCA(6SL7)VT-229 though and would be
hard put to go anywhere in a 9 pin miniature other than black plate
5751s.
David
Robert Casey
> Peter Völpel wrote:
> >
> > The ECC808 is very low on microphonics, about a third of the 12AX7.
> > Further advantages:
> > low hum when ac heated, 15µV instead 200µV with 12AX7
> > less crosstalk between the 2 triode-systems
>
> But where can you get ECC808s, and what do they cost?
>
> The only place I have ever seen any, is in my Valvo Taschenbuch...
>
How about 7025's? I get a lot less hum when I swapped out the
12AX7s with 7025s in the phono preamp of my SCA35.
Ronald Pit
Use the triodes in a ECL86 !!
"Mikkel C. Simonsen" <m...@post5.tele.dk> schreef in bericht
news:3D5561...@post5.tele.dk...
Peter Völpel
Most Klein+Hummel amplifiers used those tubes.
The 6KX8 is equivalent.
"Mikkel C. Simonsen" wrote:
>
> Peter Völpel wrote:
> >
> > The ECC808 is very low on microphonics, about a third of the 12AX7.
> > Further advantages:
> > low hum when ac heated, 15ľV instead 200ľV with 12AX7
Atomic Punk
<ldefr...@netcabo.pt> wrote:
>Hello ,
>
>I'm looking for octal "versions" of the
>12AX7 and 12BH7........
>
>Any sugestions ??
>
>Thanks in advance
>
>Luis de Freitas
>
Not sure that using the octal tubes are really going to get you
anything more than glass really. As I remember the 6SN7 were just as
prone to microphonics as the 12AX7s and the others. Maybe the added
mass of the octal socket helped bring the resonant down a little I
dont know.
I feel that hand selection of 12AX7s and 12BH7s would be easier than
dealing with harder to find 6SN7s not to mention you have a greater
flexability in choosing your sound, flat plates greys or blacks and so
on. A DC heater supply will do wonders in eliminating heater induced
hum and shielded sockets will do wonders for the stray coupling.
Happy building
AP
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