Topic: Tube rolling for a newbie

[cyberdraven]

Guys, im practically virgin in tubes so please be gentle.

I just acquired a decent el84 tube using dynaco st-35 specs.  Tube compliments are 4 RCA 6bq5 and 2 matsutcrapa 12ax7.

Can someone help me out what tubes to invest and what sonic character to expect?

Also, im toying with the idea of having a tube preamp as my next investment.  Can you give me a suggestion what tube preamp would best be used?  I wish to attain better headroom by adding preamp sana.

Thanks
Paeng

[tony]

a lot depends on your speakers, if that were mine, 90db or better sensitivity is my speaker of choice...

a pre-amp can let you get more colorations, i have some preamps that i can lend you to give you an idea...

or you can bring that amp to the house for pairing with a preamp...

about tubes, the 12ax7 should last a lifetime, it is not stressed at all, the EL84 will also last a long time
if you got them new, baka nga nagsawa ka na sa amp buo pa rin yung tubes...

or you can try borrowing from your friends before buying....

i see in the market place that they seem to take long to resell...

[audiojunkie]

I agree with sir Tony to try first before buying unless you plan to have a collection of tubes laying in your drawer....

I tried several 12ax7/ecc83 in my fisher int. amp, both at preamp & PI positions. I didn't hear any distinct difference between these tubes except when I used 5751 tubes at PI (a gift from Fr. Jim aka nizmo). This tube has lower gain than 12ax7 but music has more body than other tubes I tried.

[tony]

I agree with sir Tony to try first before buying unless you plan to have a collection of tubes laying in your drawer....

I tried several 12ax7/ecc83 in my fisher int. amp, both at preamp & PI positions. I didn't hear any distinct difference between these tubes except when I used 5751 tubes at PI (a gift from Fr. Jim aka nizmo). This tube has lower gain than 12ax7 but music has more body than other tubes I tried.

what many do not know, the mu of the tube is not its voltage gain when used in a circuit,
a mu of 100 is seldom translated to voltage gain of 100 in an actual circuit,
the tranconductance of the tube or its cathode current has more influence on voltage gain...

the 12at7 which has a mu of 60 and the 5751 with much of 70 can can have the same voltage gains
 as the 12ax7 depending on how it is used in an actual circuit...

mu is like pi of a circle, it is not a physical thing, but is the ratio of the circumference over its diameter..
plate resistance is a physical thing, it is the distance between the plate and the cathode,
transconductance is also a physical thing, it is the quality of the cathode material used
and the heating element or simply the filament...
plate resistance varies with plate voltage as tranconductance varies as the cathode current..
mu is not constant with any tube and also varies with plate voltage....
mu equals tranconductance times plate resistance...

i hope i did not confuse you more...

btw, tube rolling works because the specs of the tubes are merely statistics,
different tube manufacturers make tubes differently using different materials,
and so no one knows exactly how these tubes are with respect to published specs or datasheets...

[romeoalltheway]

Sounds greek but interesting

[tony]

Sounds greek but interesting

yes, there are more to tubes that simply pulling them out then plugging in another....

[romeoalltheway]

Actually, sir,  I've been following many of your posts with fascination. My previous knowledge of tube amps was seeing them used in my childhood in the province by the "community dance" DI some 35 years ago before I started reading your posts. Thanks for sharing your knowledge to curious minds like me. I'm just a few months in this forum, although I've loved music for a lifetime, but the increase in knowledge of technology and science behind music has leapt immensely. Thanks to you and the others for that.

[tony]

Actually, sir,  I've been following many of your posts with fascination. My previous knowledge of tube amps was seeing them used in my childhood in the province by the "community dance" DI some 35 years ago before I started reading your posts. Thanks for sharing your knowledge to curious minds like me. I'm just a few months in this forum, although I've loved music for a lifetime, but the increase in knowledge of technology and science behind music has leapt immensely. Thanks to you and the others for that.

i am posting here and in many other forums so that the so called "tube mistery" can be unmasked...
all of my postings are from a point of view of someone who builds amps and not as a consumer or end user..
spins and hypes are all around, my posts are what i call equalizers so that readers get a balanced view...

[audiojunkie]

what many do not know, the mu of the tube is not its voltage gain when used in a circuit,
a mu of 100 is seldom translated to voltage gain of 100 in an actual circuit,
the tranconductance of the tube or its cathode current has more influence on voltage gain...

the 12at7 which has a mu of 60 and the 5751 with much of 70 can can have the same voltage gains
 as the 12ax7 depending on how it is used in an actual circuit...

mu is like pi of a circle, it is not a physical thing, but is the ratio of the circumference over its diameter..
plate resistance is a physical thing, it is the distance between the plate and the cathode,
transconductance is also a physical thing, it is the quality of the cathode material used
and the heating element or simply the filament...
plate resistance varies with plate voltage as tranconductance varies as the cathode current..
mu is not constant with any tube and also varies with plate voltage....
mu equals tranconductance times plate resistance...

i hope i did not confuse you more...

btw, tube rolling works because the specs of the tubes are merely statistics,
different tube manufacturers make tubes differently using different materials,
and so no one knows exactly how these tubes are with respect to published specs or datasheets...

Confused & nose bleed...

[tony]

IOW, how sure are you that the 12AT7 you are holding now is not a relabled 12AX7?

[romeoalltheway]

i am posting here and in many other forums so that the so called "tube mistery" can be unmasked...
all of my postings are from a point of view of someone who builds amps and not as a consumer or end user..
spins and hypes are all around, my posts are what i call equalizers so that readers get a balanced view...

Indeed thanks, more power to you, sir, and all the masters of pdvd university! 

[tony]

fair warning, maraming napaso sa pagbile ng NOS tubes, ingat ingat lang pag may time....

[cyberdraven]

or you can bring that amp to the house for pairing with a preamp...

Finally!!!!  Actually sir I read most of your thread and ranting to meet you.  I tried to look for a common friend to introduce me to you.  I did PM but I think there is a problem with my account.  I work in pasig and live in lower antipolo so I am near your place.  Just let me know when I could pay you a visit.  You could also sms me at 0922 8985694.

Thanks

Paeng

[tony]

Finally!!!!  Actually sir I read most of your thread and ranting to meet you.  I tried to look for a common friend to introduce me to you.  I did PM but I think there is a problem with my account.  I work in pasig and live in lower antipolo so I am near your place.  Just let me know when I could pay you a visit.  You could also sms me at 0922 8985694.

Thanks

Paeng

i am at the house most of the time.....you are welcome to visit.....