Hi @Fuling !
My U-300B has also only 2 stages : the preamp and the power amp...
But OK, it is a vintage approach... And no direct heated preamp tube !
T
CCS/Gyrator loaded E280F and a Fet follower is high on the list of things I want to try, and my designated OPTS are also 5k.
I don't really intend to build another class A2 amp but a direct doupled Fet follower should take care of any blocking distortion.
I don't really intend to build another class A2 amp but a direct doupled Fet follower should take care of any blocking distortion.
I'd probably stick a 1:4 step-up in front and use a DHT like 26 or 10Y. That's maybe your best sounding choice. I used Hammond studio series 1140-LN-C which is nice.
SRPP with parallel 12AX7, that's a bold move🙂
tubelectron, where do you buy your chassis? They sure look good!
tubelectron, where do you buy your chassis? They sure look good!
I have the amplifier with very few components, D3a resistor loaded ) work 190v 18mA, IT Lundahl 1:1 , 300B , 420v (Anode to Cathode) 76mA , Lundahl 5k 8ohms. Simple and nice sound. 6e6p Is the first choice for replace the D3a.
After much trying.
After much trying.
I'm already using a passive transformer volume control preamp, driving a transformer with another transformer is perhaps a bit too Sakuma-esque. A Jfet buffer between them would probably be benificial.
At his point I'm only brainstorming, there are other projects in the pipeline before starting the 300B SET project. Basically I'm just bored at work, digging through old threads for inspiration.
Perhaps 6E5P would be another option then? I think I have a dozen of those somewhere.
I fhave found that the // SRPP offers gain, linearity, and low output impedance in only one full tube stage, while staying a simple, reliable design...
Here are the chassis that I use :
I buy them from Germany at https://www.banzaimusic.com/
This is my prefered format for my amp builds...
T
Thanks! 275 x 175, I could swear your amps were bigger!
I remember using 6SL7 SRPP to drive 6B4G in my first "serious" triode amp, around twenty years ago. It worked, but I seem to remember that I prefered some other versions that I tested later.
I remember using 6SL7 SRPP to drive 6B4G in my first "serious" triode amp, around twenty years ago. It worked, but I seem to remember that I prefered some other versions that I tested later.
😀 😀 😀 Yes ! But you know that I like to make compact amps ! My Stereo 10Y project will make no exception... 😉
T
tubelectron,
Built to be beautiful. Nice circuit too!
I hope you elevated the filaments of the top pair of 12AX7 triodes, with their own separate filament winding.
When I designed and built 300B SE amplifiers, the brute force DC filament supply was my favorite (similar to your design).
Your 3 each 0.45 Ohm, and 2 each 0.56 Ohm resistors keeps the 300B filaments from being "banged on" when the amplifier is powered up.
The warmed up 300B filament is 4 Ohms, but is only 1 Ohm cold.
The series 0.45/3 and series 0.56 x 2, makes a soft start 300B filament supply.
A Question for you:
Are those other output tubes KT66 or KT88?
And, are they wired as Beam Power, UL, or Triode wired?
Thanks!
Happy Listening!
Built to be beautiful. Nice circuit too!
I hope you elevated the filaments of the top pair of 12AX7 triodes, with their own separate filament winding.
When I designed and built 300B SE amplifiers, the brute force DC filament supply was my favorite (similar to your design).
Your 3 each 0.45 Ohm, and 2 each 0.56 Ohm resistors keeps the 300B filaments from being "banged on" when the amplifier is powered up.
The warmed up 300B filament is 4 Ohms, but is only 1 Ohm cold.
The series 0.45/3 and series 0.56 x 2, makes a soft start 300B filament supply.
A Question for you:
Are those other output tubes KT66 or KT88?
And, are they wired as Beam Power, UL, or Triode wired?
Thanks!
Happy Listening!
Thanks @6A3sUMMER !
I of course installed a filament bias on other SRPP preamp circuits, but I wonder if I did it on my U-300B 🤔... Not even sure 😕, since my schematic doesn't mention it (not updated ? 😡) ! They work for more than ten years as is, though...
From L to R : U-KT120, U-300B, u-OTL
The U-KT120 - as its names implies it - uses a KT120 Tung Sol tube, in a single-ended, ultra-linear, cathode bias operation. The driver stage is exactly the same SRPP circuit as on my U-300B schematic a few posts above - AND with the filament bias ! 😉
The U-OTL is an output transformer less amplifier, using 3x6080 at the output stage :
T
I like the aesthetics. It must be a challenge to keep the hum levels down?
Large or small, it is always a challenge to keep the hum levels down.
Most of my amplifiers have less than 100uV hum.
Now, I want to squeeze another balanced amplifier onto a small chassis . . .
Back to Work!
Most of my amplifiers have less than 100uV hum.
Now, I want to squeeze another balanced amplifier onto a small chassis . . .
Back to Work!
Indeed, and small chassis does not make it easier in my experience.
I've started to put the power supplies in separate chassis, it shouldn't be necessary but my speakers (12" hi eff pro drivers in corner placed horn/BR hybrids) are a bit unforgiving when it comes to hum and noise.
Thanks @Fuling !
I'd say no - assuming that you study very carefully the installation, the mutual disposition of the elements and the wiring configuration, of course - and possibly make a prototype, if you are in doubt, for checking.
The great advantage of the "compact formula" is that - if suitably designed - the connections are the shortest as possible, and then much less sensitive to inductions, coupling or losses. See below my Micro-Amp : at left Output section, center Amp/Preamp section, at right PSU section. It's not a very nice wiring per se, but it is efficient.
The CD box gives the scale of compactness of the unit - which is nonetheless perfectly hum-silent :
T
@tubelectron: Sweet looking amp!
I think I made an even smaller one once, using 2x ECL82 and transformers from old Philips radios. Not nearly as good looking as yours though, and the OPTs where marginally larger than sugar cubes and rolled off below 250Hz or so.
I think I made an even smaller one once, using 2x ECL82 and transformers from old Philips radios. Not nearly as good looking as yours though, and the OPTs where marginally larger than sugar cubes and rolled off below 250Hz or so.