Here we go, with the addition of R7 we have a jumper or dropper resistor functionality for B+ on the I/O terminals. This will allow more flexibility for folks when configuring the board at initial build out. Leaving it out keeps all the supply voltage safely away from the inputs for situations where folks would prefer the B+ to come in away from this end if the board. Not shown, but I'm also going to add a dropper resistor up by the B+ terminal. something small outline should be plenty for tossing a 1 megohm in there to keep the caps bled down.
Gonna implement these updates on the octal board too, of course.
Gonna implement these updates on the octal board too, of course.
And here we go, moved the cathode caps down a bit, got ourselves R8 in as a bleeder resistor. All changes have been put in place for both boards, as well as a surprise third board I'm working on with almost the exact same layout using dual triodes in a grounded cathode-into-cathode follower circuit that I alluded to earlier. Basically TubeCAD's CCDA circuit, more or less. It'll be a good cousin for future comparisons later on 
Her's the current state of the 6V6/6AQ5 combo board-
Her's the current state of the 6V6/6AQ5 combo board-
If I may to make a request: I would like a board for a no gain buffer with relays that would do a buffer bypass. I got myself an RME ADI-2FS DAC and I absolutely love that thing and it EQ+Tone+loudness+volume control capabilities. It has more than enough gain for me. Only thing I'd like is to add some of the tube THD to the should, but not always, for some heavy style music I mostly prefer lass distortions and compression. Thats why would be absolutely nice to have a switch to bypass the buffer connecting in to out and buffer to the ground. It should not be very difficult as we have that 6V for filaments, 5V relays should work. I think the schematics for the relays can be taken from Salas' input selector. Actually, when I thin about it, maybe something like a delay relay for the output is not a bad idea for all these versions. @Salas, @Lingwendil what do you think? Also, Happy holidays, whichever you celebrate!
Respectfully, I think if you expect a tube buffer to provide meaningful/audible amounts of THD its the wrong circuit for the application. A triode connected 6V6 is already quite linear, and using it in a cathode follower configuration will have even less THD than the gain version with the grounded cathode circuit. Not trying to dissuade you, just want to make sure you know what to expect.
You want even less gain than the 6V6 gain version and more THD in the buffer? Make a grounded cathode circuit with a 6AS7G power dual triode. Gain will be only like ~2.5 and they have really bent curves for lots of harmonic content
The relay setup is definitely something I want to work on as a standalone board at some point, as it could be used for plenty of projects for switching and muting at startup. Maybe a bit later on I'll start on something during down time. Personally I would have a use for them as well at least for startup de-thump on power amps.
Currently, my next project family after the current round of boards is going to be PSU boards. Going to do a simple mosfet ripple filter, and maybe a maida. I previously did a mosfet board but it's kind of goofy and I want to change a few things on it since I need to have more made anyway.
You want even less gain than the 6V6 gain version and more THD in the buffer? Make a grounded cathode circuit with a 6AS7G power dual triode. Gain will be only like ~2.5 and they have really bent curves for lots of harmonic content
The relay setup is definitely something I want to work on as a standalone board at some point, as it could be used for plenty of projects for switching and muting at startup. Maybe a bit later on I'll start on something during down time. Personally I would have a use for them as well at least for startup de-thump on power amps.
Currently, my next project family after the current round of boards is going to be PSU boards. Going to do a simple mosfet ripple filter, and maybe a maida. I previously did a mosfet board but it's kind of goofy and I want to change a few things on it since I need to have more made anyway.
Alright guys, think this may be it- I've adjusted a few things, upsized all the small component lead through-holes to 2mm diameter, and updated all the boards to suit the changes. One nice thing about this unified design is that all you need to do is cut the holes big enough for the octal sockets at initial build out, and then for a swap simply unbolt the board and attach the wiring to the screw terminals. Easy peasy!
Design goals that I believe we have covered-
-Parallel anode load resistors for better heat dissipation (and holes for ventilation)
-Through-hole so that components can be put on either side (I like putting power resistors up top, for example)
-Screw terminals for easy connection without solder
-Offboard filament wire routing, with onboard screw terminal connector for ease of use, allows AC or DC heating, series/parallel options
- Power entry at either end of board for experienced users, with beginner friendly jumper/resistor option to keep B+ away from input terminals if using opposite power terminal
-40mm mounting screw spacing for Belton sockets with integrated flange
-Centered 3mm hole under each socket to assist in layout of chassis holes, as well as mounting LEDs if you so desire
-On-board power bleed resistor to discharge PSU capacitor
-Easy to understand silkscreening of component labels that are similar on each channel (Example, channel one= R1, channel two=R21)
-Multiple capacitor lead footprints to accommodate multiple sizes of common DC-link types as well as axial lead audio types
Other than some minor adjustments to the silkscreen labels for some components they're basically done.
Here is the Octal/6AQ5 board-
Here is the Noval/6p43p/6p14p/6p15p board-
Here is the third surprise board, a 9AJ dual triode noval board based on the same layout and mounting arrangement. May be fun for quick comparison using tubes like the 6CG7/6FQ7, 6n1p, and the ubiquitous 12AU7 types. This is something I've had a ton of requests for, and a personal need for so it was trivial to make a variant to use them. It's a simple gain stage direct coupled to a cathode follower, basically like TubeCAD's CCDA article. I have a ton of 6CG7/6FQ7 and will put together a board for a pair for general use.
Think I may order 10 Octals, 5 novals, and 5 of the 9AJ boards. I'll do some quick checks, transfer everything over from the existing prototypes, and see how they do. Thinking of sticking with blue for the Salas design PCBs, considering purple for the 9AJ boards.
If these look good I'll release the files, and move on to power supplies. The biggest pain in my rear on tube circuitry is lashing together power supplies, so I really want to have some 50x100mm companion boards, and I need to update my mosfet pi filter boards to something nicer anyway.
Do y'all still like Maida regulators for these builds? Wonder if I can fit a decent implementation of one on a 50x100 board. 🤔
Design goals that I believe we have covered-
-Parallel anode load resistors for better heat dissipation (and holes for ventilation)
-Through-hole so that components can be put on either side (I like putting power resistors up top, for example)
-Screw terminals for easy connection without solder
-Offboard filament wire routing, with onboard screw terminal connector for ease of use, allows AC or DC heating, series/parallel options
- Power entry at either end of board for experienced users, with beginner friendly jumper/resistor option to keep B+ away from input terminals if using opposite power terminal
-40mm mounting screw spacing for Belton sockets with integrated flange
-Centered 3mm hole under each socket to assist in layout of chassis holes, as well as mounting LEDs if you so desire
-On-board power bleed resistor to discharge PSU capacitor
-Easy to understand silkscreening of component labels that are similar on each channel (Example, channel one= R1, channel two=R21)
-Multiple capacitor lead footprints to accommodate multiple sizes of common DC-link types as well as axial lead audio types
Other than some minor adjustments to the silkscreen labels for some components they're basically done.
Here is the Octal/6AQ5 board-
Here is the Noval/6p43p/6p14p/6p15p board-
Here is the third surprise board, a 9AJ dual triode noval board based on the same layout and mounting arrangement. May be fun for quick comparison using tubes like the 6CG7/6FQ7, 6n1p, and the ubiquitous 12AU7 types. This is something I've had a ton of requests for, and a personal need for so it was trivial to make a variant to use them. It's a simple gain stage direct coupled to a cathode follower, basically like TubeCAD's CCDA article. I have a ton of 6CG7/6FQ7 and will put together a board for a pair for general use.
Think I may order 10 Octals, 5 novals, and 5 of the 9AJ boards. I'll do some quick checks, transfer everything over from the existing prototypes, and see how they do. Thinking of sticking with blue for the Salas design PCBs, considering purple for the 9AJ boards.
If these look good I'll release the files, and move on to power supplies. The biggest pain in my rear on tube circuitry is lashing together power supplies, so I really want to have some 50x100mm companion boards, and I need to update my mosfet pi filter boards to something nicer anyway.
Do y'all still like Maida regulators for these builds? Wonder if I can fit a decent implementation of one on a 50x100 board. 🤔
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Couldn't leave it alone, changed out the filament termnal from a 2 position to a 3 position, that way we can feed the filaments with individual CCS leads if so desired, with a common return/ground wire. You can still populate it with a 2 position if not needed. Gonna scoot a few things around to get the ground end of R3/R23 further away for proper connection to the ground plane.
In progress transferring this feature to all boards.
Also doing little picky-choosy tweaks here and there but I'm ready to call it done, otherwise I'll never stop adjusting it.
In progress transferring this feature to all boards.
Also doing little picky-choosy tweaks here and there but I'm ready to call it done, otherwise I'll never stop adjusting it.
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Made a few adjustments and ordered some boards! Money is tight so this batch is 15 octal boards, 10 noval boards, and 10 of the 9AJ boards. Should be 10-16 day shipping once processed. Once I get this batch in I'll be populating one of each and then we will start a new thread for the sales and all the money side of things.
All the boards are blue this time as well.
JLCPCB is good for small batches but gets a bit pricy when you need more than 10 each and the shipping gets up there quickly. Might look into another vendor if there's enough interest to justify more than a few dozen in a single batch.
All the boards are blue this time as well.
JLCPCB is good for small batches but gets a bit pricy when you need more than 10 each and the shipping gets up there quickly. Might look into another vendor if there's enough interest to justify more than a few dozen in a single batch.
Alright, now that the other PCBs are done- I moved on to one final variant before moving on to PSU work- As a few have asked and it's really no trouble to do, I was able to split off a variant with a noval socket nested inside the octal footprint to accommodate the 6P1P as well. To my knowledge there are no other nine-pin tubes that share the same pinout as the bastard 6P1P, but this board rounds us out on all the 6V6 family variants. I may order a set of these to have handy next time I make a PCB order.
With this addition, we can now support the following tubes with this family of boards-
Octal/7pin board- 6V6, 12V6, 6K6, 6W6, 6P6S, 6L6, with addition of EL90/6AQ5,12AQ5, 6005
Octal/9pin board- 6V6, 12V6, 6K6, 6W6, 6P6S, 6L6, with addition of 6P1P
Noval/9pin board- 6BW6, 6BQ5/EL84/6P14P, 6CW5/EL86, 6P43P-E, 6P15P
One could also run the EL34 and similar pinout tubes if tying the cathode and G3 pins together, but I doubt this will be a common use scenario.
A board for everyone? Looks like between this anf the 9AJ boards I'm doing one could build something to fit darn near every single-bottle per channel preamp configuration imaginable. Maybe I should also do an octal companion to the 9AJ board now too for 6SN7/6SL7?
With this addition, we can now support the following tubes with this family of boards-
Octal/7pin board- 6V6, 12V6, 6K6, 6W6, 6P6S, 6L6, with addition of EL90/6AQ5,12AQ5, 6005
Octal/9pin board- 6V6, 12V6, 6K6, 6W6, 6P6S, 6L6, with addition of 6P1P
Noval/9pin board- 6BW6, 6BQ5/EL84/6P14P, 6CW5/EL86, 6P43P-E, 6P15P
One could also run the EL34 and similar pinout tubes if tying the cathode and G3 pins together, but I doubt this will be a common use scenario.
A board for everyone? Looks like between this anf the 9AJ boards I'm doing one could build something to fit darn near every single-bottle per channel preamp configuration imaginable. Maybe I should also do an octal companion to the 9AJ board now too for 6SN7/6SL7?
You forgot 6P3S, KT66, KT77, KT88, KT90, KT120, KT150 (and if you add a connection for a plate cap at octal pin 3 also 6DQ6, 6BQ6, 6P31S, 6CM5 etc)With this addition, we can now support the following tubes with this family of boards-
Octal/7pin board- 6V6, 12V6, 6K6, 6W6, 6P6S, 6L6, with addition of EL90/6AQ5,12AQ5, 6005
Octal/9pin board- 6V6, 12V6, 6K6, 6W6, 6P6S, 6L6, with addition of 6P1P
I mean I doubt anyone would use those power tubes for a preamp, but I wouldn't use a 6V6 either so who can say? Far too much money though for me though. 6P1P though? Awesome preamp using $1 tubes!
Two guys tried it in this thread as far as I remember. On full gain. They had more hum and its harmonics in the FFT but they said it wasn't directly annoying yet. I am sure it covers some audio detail when well measurable vs DC.
AC heating can not only couple to the cathode, it can couple on signal wires and parts too. Needs expert build.
AC heating can not only couple to the cathode, it can couple on signal wires and parts too. Needs expert build.