did you try using the other half of the dual triode as a current sink rather than the 33k/3w resistor? sorry if i missed it in the thread somewhere
At start-up, you'll have -225 V on the grid of the 300B. I don't see an issue with that. It shuts the 300B completely off so no current flows. As the cathode follower warms up, the grid voltage of the 300B stabilizes to the desired value. It's a pretty well-controlled process. The current in the 300B ramps smoothly without tendency to overshoot.
If you replaced the 33 kΩ, 3 W resistor with a CCS, you'd still have -225 V at start-up. Unless you use a tube-based CCS. Then you probably have a floating grid until the CCS warms up. You definitely do NOT want that.
~Tom
If you replaced the 33 kΩ, 3 W resistor with a CCS, you'd still have -225 V at start-up. Unless you use a tube-based CCS. Then you probably have a floating grid until the CCS warms up. You definitely do NOT want that.
~Tom
Last edited:
Hi,
Does anyone have experience running this amplifier without a preamp? I'm very interested in building it, but I'm not sure if it has enough gain to be workable in my system.
I would be running it single ended, so no input transformers, and I would use a volume control at the input like Scleratus. My CD player is standard 2V output and my speakers are about 94 dB/W/m. I don't listen very loud, but I still need a decent level of volume.
Thanks
Does anyone have experience running this amplifier without a preamp? I'm very interested in building it, but I'm not sure if it has enough gain to be workable in my system.
I would be running it single ended, so no input transformers, and I would use a volume control at the input like Scleratus. My CD player is standard 2V output and my speakers are about 94 dB/W/m. I don't listen very loud, but I still need a decent level of volume.
Thanks
The DG300B (aka DeathTrap 400) is still my daily driver, actually. I built two of them for a bi-amp configuration. My speakers are 87 dB/W*m efficient and my listening position about 2 m from the speakers in a reasonably sized living room. For background music, my preamp volume control sits below -30 dB. For more critical listening, I crank it up into the -20ies dB. Only when I really crank it, does the preamp ever get near 0 dB. That results in SPL high enough to make my ears ring, even with my relatively inefficient speakers.
The gain of the amp is about 5x (14 dB) with the E88CC/6922 tubes and 3.4x (11 dB) with the 6N6P/ECC99 tubes.
I still have a couple of circuit boards for this amp, if you're interested. You can find them on my website: DG300B SET Amp.
~Tom
The gain of the amp is about 5x (14 dB) with the E88CC/6922 tubes and 3.4x (11 dB) with the 6N6P/ECC99 tubes.
I still have a couple of circuit boards for this amp, if you're interested. You can find them on my website: DG300B SET Amp.
~Tom
Last edited:
Hi Tom,
A couple more questions - what is the output impedance of the amplifier? And do you use negative feedback? I'm asking because whenever I've tried to use single ended tubes with no NFB on my speakers, they have always produced a very skewed frequency response (a hump in the mid bass, way, way too much treble and a broad recession through the midrange). Nominal impedance of the speakers is 8 ohms.
Thanks,
Bill
A couple more questions - what is the output impedance of the amplifier? And do you use negative feedback? I'm asking because whenever I've tried to use single ended tubes with no NFB on my speakers, they have always produced a very skewed frequency response (a hump in the mid bass, way, way too much treble and a broad recession through the midrange). Nominal impedance of the speakers is 8 ohms.
Thanks,
Bill
I've actually never measured the output impedance directly. I have looked at the output voltage vs input voltage into a resistive load. I recall that being very linear, indicating a low output impedance. I don't have a number for you though.
There's no global negative feedback in the amp.
My 8 Ω speakers measured as flat with the DG300B as they do with a sand amp that I know has very low output impedance and a flat frequency response. I measured using a calibrated measurement microphone placed about 1 m from the speakers.
~Tom
There's no global negative feedback in the amp.
My 8 Ω speakers measured as flat with the DG300B as they do with a sand amp that I know has very low output impedance and a flat frequency response. I measured using a calibrated measurement microphone placed about 1 m from the speakers.
~Tom
Tom,
Thanks for the answers. I'm not completely sure the DG300B will work in my system, but I'm sure enough that I just went ahead and ordered the boards ;-)
I probably won't spend serious money on tubes or iron until I know that the gain and frequency response will work for me, but I'm really looking forward to the build and hearing what the 300B has to offer.
Best regards,
Bill
Thanks for the answers. I'm not completely sure the DG300B will work in my system, but I'm sure enough that I just went ahead and ordered the boards ;-)
I probably won't spend serious money on tubes or iron until I know that the gain and frequency response will work for me, but I'm really looking forward to the build and hearing what the 300B has to offer.
Best regards,
Bill
Looking forward to it. I'll be honest, I love to have test results from competent designs to compare to when I build things. I would be interested in a Zout measurement if you get the time. I'd be curious to know what the Zout of a 300B SE amp with quality transformers is in practice.
Hi Tom,
Re: your post:
Do you plan to make another run of DG300B PCBs when you run out? I want to build it, but I'm not ready to start a new project yet.
If you aren't planning to reprint the 300B PCBs then I'll grab them now, but I expect there might be some slight tweaks on a new version?
Thanks,
Rich
Re: your post:
Do you plan to make another run of DG300B PCBs when you run out? I want to build it, but I'm not ready to start a new project yet.
If you aren't planning to reprint the 300B PCBs then I'll grab them now, but I expect there might be some slight tweaks on a new version?
Thanks,
Rich
I have no plans for updating the DG300B PCB. I spent about 2-3 years prototyping and trying various circuits. I really like the circuit the way it is. The DG300B has been my daily driver amp since it was in the early stages of prototyping. I really enjoy it. I'm confident the DG300B is the best circuit I can design with the 300B.
I actually built two stereo amplifiers using the DG300B PCBs. I use them in a bi-amp configuration. They both perform as well now as they did when they were put into service.
I have 15-20 boards left. I have not decided if I will order more once I run out. That really depends on the demand at that time. If you want the entire board set (including the Universal Filament Regulator boards), I suggest that you order now rather than wait...
~Tom
I actually built two stereo amplifiers using the DG300B PCBs. I use them in a bi-amp configuration. They both perform as well now as they did when they were put into service.
I have 15-20 boards left. I have not decided if I will order more once I run out. That really depends on the demand at that time. If you want the entire board set (including the Universal Filament Regulator boards), I suggest that you order now rather than wait...
~Tom
I have some of Tom's Universal Filament Regulator boards setup for feeding 813 filaments (10V@5A)
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.