Tube DI Box

[ruffrecords]

Thanks Merlin. It should be somewhat better with something like a VTB2291 wired 2:1 step down.

Cheers

ian

 

[ruffrecords]

OK, here is a draft schematic for the tube DI box PCB. The idea is that it is flexible enough that you can build almost any version with it:



The lower triode can be configured as either an SRPP, mu follower, White follower or single ended input stage. The top triode can be configured to complement the bottom triode configuration and in the case of the single ended input stage, the top triode can be configured as a cathodyne or a simple cathode follower output stage.

There are four connectors: HT, heaters, input and transformer. If we keep the HT on the top triode down to 250V there should be no need for heater elevation.

Cheers

Ian

 

[Wavelength]

Ian,
Been traveling a lot so where is this project at? Before I left I did a parallel 6922 loaded with a 140H/12ma (49% nickel [intact audio] running at 9.7ma or ~4.8ma each, Vdc drop 5.1V) at 80V using the NMT0572. Input supply was 8V regulated took that down to 6.3V for the filament diode->into the NMT and then grounded the -72V terminal and output on ground. I have used these in many USB dacs with 12AU7 tubes as buffers. It's best to use 3 caps and bypass each leg no matter if used or not.
Anyway the results were killer into a 5K:500 output I had which was a modified Peerless design the frequency response was dead on 10-52K -1dB. Too bad I can't get more of these as we lost Mike LaFevre (MagneQuest) last summer.
Anyway catching up on this tread.
Thanks,
Gordon

 

[ruffrecords]

In summary, there are a number of alternative ways or building this. The above schematic tries to capture most of them and I am currently working on a PCB layout that will allow you to build any one of them.

From the safety/regs point of view and external SMPS seems the best option with a little dc:dc boost supply for the HT.

When the PCB design is complete I will have a bunch made. Happy to give them away to anyone interested in building a version.

Cheers

Ian

 

[Mondy]

I believe the project is in Ian's safe hands and I for one are eagerly looking forward to seeing what designs he comes up with for this tube DI.

I appreciate that this remit could be realised using load chokes with outstanding performance, but I would be more than glad to see designs that minimise the requirements for exotic iron as these days you have to pay crazy money for what are essentially simple components. We have enough issues sourcing power and output transformers for this type of build!!