12AX7+12AU7 Classic China Amplifier "Marantz 7" style circuit?
Recently a friend donated me some NOS 6189W tubes they are basically 12AU7 mil-type. I wanted a simple easy circuit to plug them into. I decided to buy one of these kit preamps from Aliexpress. This one is from DIYBox store but there are a few others that sell this kit and some say "Marantz 7" style.
Just wondering if anyone has experience with them and can suggest tuning and mods for it. It probably needs some tuning or adjustments to optimize the circuit for the 6189W so i'm all ears. The PCB quality is very good.
The kit is basically:
Recently a friend donated me some NOS 6189W tubes they are basically 12AU7 mil-type. I wanted a simple easy circuit to plug them into. I decided to buy one of these kit preamps from Aliexpress. This one is from DIYBox store but there are a few others that sell this kit and some say "Marantz 7" style.
Just wondering if anyone has experience with them and can suggest tuning and mods for it. It probably needs some tuning or adjustments to optimize the circuit for the 6189W so i'm all ears. The PCB quality is very good.
The kit is basically:
- 115VAC 30VA 0-220 / 0-16V R-CORE Transformer
- 12AX7+12AU7 Classic Circuit Tube Preamplifier Board
- 12V and HV Regulator Board
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The wise thing to do is first to get it going, then think about tuning.
Otherwise you'll be going around in circles ad infinitum.
jan
Otherwise you'll be going around in circles ad infinitum.
jan
Maybe use the 12AU7 (or the 6189) as a cathode follower: less gain and low output impedance?
That would be my rec. as well, but you might as well wire it p-p, and not bother with the PCB.
I like the enclosure. I wonder if that came from the same store?
jeff
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cool - should "sound good". A second board could be added and use ax7 in the second position as a Hegeman tribute phono preamp with the 12ax7 cascade feedback pair with gain set to ~100 driving passive lumped RIAA eq (per Citation I and Citation IV) An anode follower au7 can be good for a low gain line stage as alternative to CF.
I used to write back and forth with a retired engineer and his Dyna
PAS type line stage ran 400vdc B+ with care to loadlines, etc.. The feedback resistor coming off the 2nd tube's plate to the first stage's cathode was 15K. I thought that would bog down and rotate the 2nd tube's loadline in a bad way but he explained it was adding in "quadrature". Would anyone here care to elaborate on what he said?
I used to write back and forth with a retired engineer and his Dyna
PAS type line stage ran 400vdc B+ with care to loadlines, etc.. The feedback resistor coming off the 2nd tube's plate to the first stage's cathode was 15K. I thought that would bog down and rotate the 2nd tube's loadline in a bad way but he explained it was adding in "quadrature". Would anyone here care to elaborate on what he said?
Perhaps "quadrature" refers to quadratic, where he's bringing up the coefficient value on the squared term, relative to the linear...
Square a sine you get 2X the frequency, so it's possibly bringing up a second harmonic level. I've been to the dentist between the beginning and end of that sentence ;')
Ok my first question is: is Rcore transformer supposed to be mounted directly to chassis or on insulated studs/standoffs?
I got the same board for $5ish on ebay and with some small mods, I used it
for my lockdown project st35 based on diytube schematic....the amp is a kinda quick-n-dirty
build, but it is dead quiet and works great.
Here is the diytube st35 schematic as built on this board - ( refer to
http://www.diytube.com/phpBB2/viewtopic.php?f=1&t=6029 )
for my lockdown project st35 based on diytube schematic....the amp is a kinda quick-n-dirty
build, but it is dead quiet and works great.
Here is the diytube st35 schematic as built on this board - ( refer to
http://www.diytube.com/phpBB2/viewtopic.php?f=1&t=6029 )
By quadrature he means the root of the sum of the squares:
Rtotal = sqrt (R1^2 + R2^2)
However, I don't know exactly what aspect of the circuit he thinks follows this rule. You are quite right that a small feedback resistor would load the stage.
I want a really simple preamp to put in front of my Aleph J. I've decided not to build this circuit.1) i'm told it is unity gain 2) I don't really want to do all the hacking with the trace cuts and jumps. I am probably just going to use the RCA Radiotron circuit with my own PCB layout. If anyone is interested in the PCB for the RCA line amp using 12AU7. I will offer a few for sale when they come in:
Attachments
A better choice may be something like the CCDA from TubeCAD, it'll be a similar circuit and PCBs are available from TubeCAD, and I even have my own version I recently developed as well-
https://www.tubecad.com/2009/03/blog0161.htm
Here's a simple schematic with basic info, for a 12AU7 something like 22k Rload, 560R Rk would be a decent starting point-
Here's a multi-layer view of my variant of the PCB- I'll be releasing the design files once I have them in hand to test functionality.
One bottle per channel and simple easy parts values.
https://www.tubecad.com/2009/03/blog0161.htm
Here's a simple schematic with basic info, for a 12AU7 something like 22k Rload, 560R Rk would be a decent starting point-
Here's a multi-layer view of my variant of the PCB- I'll be releasing the design files once I have them in hand to test functionality.
One bottle per channel and simple easy parts values.
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Hello, I am building the tube preamp and power supply board like the one built by my first amplifier. I have a question. The power supply board kit has a couple of designations of L1 and L2. I am trying to figure out if these are for a couple of inductors or chokes and what the values of L1 and L2 should be. Since this board comes with no schematic, I am a bit stumped. Has anyone completed the build of this board and if so, would you mind sharing what you used. Thanks.