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Offline meat_eater

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Schematic inquiry
« on: Jun 18, 2013 at 09:50 PM »
Hi guys

Based sa schematic sa baba, anu po ung use ng 12ax7 and 12au7 sa circuit?

And if I were to experiment on rolling, what tube will affect the overall sound more? the 12ax7 or the 12au7?



Thanks mga chief!

 :)
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Offline JojoD818

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Re: Schematic inquiry
« Reply #1 on: Jun 19, 2013 at 12:04 AM »
The first half of your input tube 12AX7 forms a voltage amplifier that pumps up the input signal and is direct coupled to the other half of your 12AX7 which is a cathode follower, essential to increase current drive and lower output impedance (of that stage).

The signal is then fed to your 12AU7 that forms a phase splitter or a cathode follower differential amplifier. Notice that the second triode of your 12AU7 is fed via a 1K resistor with a 0.1uf capacitor which inverts the signal necessary for the output tubes so that when one "push", the other "pulls". Hence, a fixed bias Class AB push-pull amplifier. The presence of -V1 and -V2 on the output tube's grid makes it a fixed bias type.

IMHO, in terms of tube rolling, the input tube (12AX7) shall give you the biggest difference in "flavor". Improvements though in the phase splitter like using a CCS circuit in place of that 22K resistor makes a night and day difference in terms of electrical performance and sonic properties.

HTH. Happy tubing!

Cheers


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Offline meat_eater

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Re: Schematic inquiry
« Reply #2 on: Jun 19, 2013 at 05:12 AM »
Thanks so much sir! Wala kasi ako background sa engineering, I just wanted to have a better understanding on this subjective hobby of ours, kesa salpak lang ng salpak.

Thanks sir! :)
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Offline ATJr.

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Re: Schematic inquiry
« Reply #3 on: Jun 19, 2013 at 06:13 AM »
these are your options, instead of just rolling with the same tube number,
you can also try other numbers from different brands....
the 12au7 is a long-tail pair phase splitter, also  called a differential amplifier, it can be replaced with a 12bh7, 12ay7, the 12ax7 voltage amp can be replaced with a 7025, 5751, 6201, 12at7, 12az7, 12bz7......
« Last Edit: Jun 19, 2013 at 07:05 AM by ATJr. »
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Offline meat_eater

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Re: Schematic inquiry
« Reply #4 on: Jun 19, 2013 at 07:48 AM »
Quote from: ATJr. on Jun 19, 2013 at 06:13 AM
these are your options, instead of just rolling with the same tube number,
you can also try other numbers from different brands....
the 12au7 is a long-tail pair phase splitter, also  called a differential amplifier, it can be replaced with a 12bh7, 12ay7, the 12ax7 voltage amp can be replaced with a 7025, 5751, 6201, 12at7, 12az7, 12bz7......


I did replace the stock chinese tubes nuon, although I did blindly, and just hoped for the better since I had no idea how the circuit works. Hehehe. Luckily, I did get very good results from some nos GEs and Sovteks.. Although the used tubes were the same codes. I'm thinking of the 5751 and the CV4004, research research lang onti. Hehehe. Thanks sir!! :)
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Offline JojoD818

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Re: Schematic inquiry
« Reply #5 on: Jun 20, 2013 at 07:26 AM »
Quote from: meat_eater on Jun 19, 2013 at 05:12 AM
Thanks so much sir! Wala kasi ako background sa engineering, I just wanted to have a better understanding on this subjective hobby of ours, kesa salpak lang ng salpak.

Thanks sir! :)


Tubes are very forgiving devices, they're a child's play in electronics, SS are sometimes like that too. But if you really want to change the sound or maximize the sonics, you have to dig in there. How it's all whipped up inside is what makes a NAD sound like a NAD, and a Rotel to sound like a Rotel. If you have the money to burn, transplant an Edrel output transformer in there.
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Offline ATJr.

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Re: Schematic inquiry
« Reply #6 on: Jun 20, 2013 at 07:33 AM »
couldn't have said it any better jojod,
the output transformer i would say is
the heart and soul of your tube amp,
it was the OPT in the Dyanco ST 70
that made it sell like hotcakes back in the day....

i have seen china amps that used OPT's in a KT88 pp amp,
the size of the irons are like those that i have seen
in a Dyna ST35, well talk about miniaturization...:D
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Offline JojoD818

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Re: Schematic inquiry
« Reply #7 on: Jun 20, 2013 at 07:40 AM »
miniaturization... ;D I bet they're cheating!  >:(

unless they've invented a new type of core and a turns ratio like no other then that's just plain cost cutting.
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Offline ATJr.

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Re: Schematic inquiry
« Reply #8 on: Jun 20, 2013 at 07:59 AM »
Quote from: JojoD818 on Jun 20, 2013 at 07:40 AM
miniaturization... ;D I bet they're cheating!  >:(

unless they've invented a new type of core and a turns ratio like no other then that's just plain cost cutting.

miniaturization...this is the polite and politically correct way of saying what you just said..... :D >:D
Edrel's irons otoh are world class.... 8)
« Last Edit: Jun 20, 2013 at 08:00 AM by ATJr. »
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Offline JojoD818

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Re: Schematic inquiry
« Reply #9 on: Jun 20, 2013 at 08:56 AM »
remind me to appoint you as my chief press secretary when I'm president  ;D ;D ;D


I once read a guy in DA post, how to hide a 7/8" core opt for an el34? put it in a large epoxy filled tin box and have it auto painted. geez. ;D
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Offline ATJr.

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Re: Schematic inquiry
« Reply #10 on: Jun 20, 2013 at 09:20 AM »
LOL!!! who is to know? di naman nila alam yon..... ;) >:D

the thing with small irons is that
it seems to do better in the mids and highs,
kaya lang if you are a bass type guy,
lagi kang bitin lalo na kung malakas ka magplay...
OPT's rely on the cores up to about 400hz,
beyond that you can just as well use an air core traffo...
« Last Edit: Jun 20, 2013 at 11:16 AM by ATJr. »
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Offline JojoD818

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Re: Schematic inquiry
« Reply #11 on: Jun 20, 2013 at 11:01 AM »
exactly! di man lang nirespeto yun 20hz-20khz na convention...  :D :D :D

kaya pala hindi umiinit...  :P
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Offline ATJr.

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Re: Schematic inquiry
« Reply #12 on: Jun 20, 2013 at 11:20 AM »
the first and the last thing i look at in any tubed amp is the irons...
yung tubes madaling makabile at magpalit....
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Offline JojoD818

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Re: Schematic inquiry
« Reply #13 on: Jun 20, 2013 at 11:24 AM »
elementary na yan tubes ;D
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Offline ATJr.

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Re: Schematic inquiry
« Reply #14 on: Jun 20, 2013 at 11:52 AM »
those china amps are indeed good looking so that it is hard to ignore them...
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