Has anybody built a set up for KT88/6550, 300B, or 845 who could share experiences and ideally, a BOM and what you did for supply voltages? I think there was talk of tailored BOMs, but it looks to me like the thread never got that far, even for the KT88/6550.
Paul
Paul
I have a pair of stuffed boards here and I would be keenly interested in seeing a KT88 version built and documented as well.
I know that it once existed as I made a video of it running. Now, if I could only find my notes. Video is here:
I have been contemplating the construction of "The BIG one" for some time. If I can get all the other stuff off the bench, I'll try the UDB + UNSET Octal Output Board combination. Once that is stable and working, it's only a matter of adding more UNSET output boards and building a power supply capable of feeding a 1KW tube amp.
I have been enjoying the KT88 mono-blocks I built with using the UDB boards for several years now. They sound great. Attached is a version of the BOM, (I'm guessing it is the final one) along with a schematic that George drew of the power supply needed. I hope this is helpful. Enjoy
The original Universal Driver Board has a long and winding story behind it with some long periods of time where it was ignored. I had created an amp called the 300Beast in about 2000 in which I simply cut and pasted some of the trendiest circuits found on the web together. Despite having far too much gain, it worked pretty good but fell into disuse and got stripped for parts a few years back. The first two stages were the starting point for a new P-P driver design.
The first iteration of the UDB was made on a turret board in 2007. I slapped it together so I could test some big sweep tubes in conventional G1 drive as well as screen (G2) drive applications where huge AC drive voltages are needed. Despite the obvious physical differences, both tubes were always 6SN7's. This thing went through several changes as the needs dictated and got used a lot. There was obviously at least one attempt at a PC board back in 2007 and KT88's were involved. 2007 and 2008 brought a lot of challenges with the death of my father and Sherri's stepfather, a bout with recurring aggressive skin cancer and a job change. The board sat on the bench unused a lot.
In 2008 I had begun to tinker with tubes again and a question was asked on diyAudio which got the board out of the box where unused boards go to be relieved of useful parts. That happened in post #94 in this thread which evolved into a Push Pull 6L6GC amp in Australia, and the UDB here over nearly 4 years.
By 2010 I could see that Motorola was on a long slow downsizing / offshoring of the plant where I worked, and tech in general was dying off in South Florida so plans were put in motion for my eventual retirement which did come far earlier than I expected. There were several road and air trips between South Florida and West Virginia with lots of down time due to health issues with relatives. I used that time to lay out PC boards on my laptop. I still have at least 20 completed or partially completed designs of several tube and solid state PC boards related to audio reproduction or music synthesizers on my hard drive. In 2013 I accepted a buyout offer from Motorola, which got delayed twice. I left Florida in July of 2014. We were in temporary housing for about a year while this house was being built so little electronics work occurred. I did take the best ideas from several versions of push pull driver boards, roll it all into one good board and sent it out to a board shop. The boards sat in the box for several months until I had a minimal workbench set up in the new house. Just as the push pull amp experiments got going full steam, I had to revisit the original TSE since Sharp had discontinued the filament regulator chip and a weasel bought up all of the remaining US stock. This upheaval caused some delay, but resulted in the TSE-II design which is larger and far less crowded than the original TSE which was really designed for 45 tubes. It uses a different filament regulator, but the same proven audio path on a larger board with improved thermal management.
Post # 630 in the 6L6-AB2 thread shows one of the current UD boards after I made a minimal change to replace some LED's with real voltage reference chips. The board has remained unchanged ever since, it just works. Unfortunately, during all of the often unscheduled movement lots of stuff got lost including a whole moving box full of documentation.
The test setup seen here in pictures #487 and 490 still exists but is being refitted with UNSET output boards for some high power amp experimentation. I have used this same pair of UDB's for several experiments with small (6V6GT, 6K6, 6W6) tubes and big sweeps like the 26HU5 and 6LW6. I'll create a parts list from these boards once I finish the PC build mess that has taken over the workbench.
The first iteration of the UDB was made on a turret board in 2007. I slapped it together so I could test some big sweep tubes in conventional G1 drive as well as screen (G2) drive applications where huge AC drive voltages are needed. Despite the obvious physical differences, both tubes were always 6SN7's. This thing went through several changes as the needs dictated and got used a lot. There was obviously at least one attempt at a PC board back in 2007 and KT88's were involved. 2007 and 2008 brought a lot of challenges with the death of my father and Sherri's stepfather, a bout with recurring aggressive skin cancer and a job change. The board sat on the bench unused a lot.
In 2008 I had begun to tinker with tubes again and a question was asked on diyAudio which got the board out of the box where unused boards go to be relieved of useful parts. That happened in post #94 in this thread which evolved into a Push Pull 6L6GC amp in Australia, and the UDB here over nearly 4 years.
By 2010 I could see that Motorola was on a long slow downsizing / offshoring of the plant where I worked, and tech in general was dying off in South Florida so plans were put in motion for my eventual retirement which did come far earlier than I expected. There were several road and air trips between South Florida and West Virginia with lots of down time due to health issues with relatives. I used that time to lay out PC boards on my laptop. I still have at least 20 completed or partially completed designs of several tube and solid state PC boards related to audio reproduction or music synthesizers on my hard drive. In 2013 I accepted a buyout offer from Motorola, which got delayed twice. I left Florida in July of 2014. We were in temporary housing for about a year while this house was being built so little electronics work occurred. I did take the best ideas from several versions of push pull driver boards, roll it all into one good board and sent it out to a board shop. The boards sat in the box for several months until I had a minimal workbench set up in the new house. Just as the push pull amp experiments got going full steam, I had to revisit the original TSE since Sharp had discontinued the filament regulator chip and a weasel bought up all of the remaining US stock. This upheaval caused some delay, but resulted in the TSE-II design which is larger and far less crowded than the original TSE which was really designed for 45 tubes. It uses a different filament regulator, but the same proven audio path on a larger board with improved thermal management.
Post # 630 in the 6L6-AB2 thread shows one of the current UD boards after I made a minimal change to replace some LED's with real voltage reference chips. The board has remained unchanged ever since, it just works. Unfortunately, during all of the often unscheduled movement lots of stuff got lost including a whole moving box full of documentation.
The test setup seen here in pictures #487 and 490 still exists but is being refitted with UNSET output boards for some high power amp experimentation. I have used this same pair of UDB's for several experiments with small (6V6GT, 6K6, 6W6) tubes and big sweeps like the 26HU5 and 6LW6. I'll create a parts list from these boards once I finish the PC build mess that has taken over the workbench.
Attachments
A few years ago I built up a UDB with one of George’s PCBs and used it for testing 6HJ5s in crazy-drive configuration. The UDB performed perfectly, but the crazy-drive distortion test results were very disappointing.
Sometime later I decided to replace the amplification, phase splitter and driver stages of the first 2 amps I built, 6550 Williamson’ish mono-blocks, with UDBs. I did some testing and the results were excellent so I made up my own PCBs in order to use the existing tube holes in the chassis, loaded and tested one. Then other projects (a 300B TSEII and a higher power Engineer’s Amp) put that on the back-burner.
Having now completed those 2 projects I’ve resurrected the Williamson amp UDB upgrade project.
Sometime later I decided to replace the amplification, phase splitter and driver stages of the first 2 amps I built, 6550 Williamson’ish mono-blocks, with UDBs. I did some testing and the results were excellent so I made up my own PCBs in order to use the existing tube holes in the chassis, loaded and tested one. Then other projects (a 300B TSEII and a higher power Engineer’s Amp) put that on the back-burner.
Having now completed those 2 projects I’ve resurrected the Williamson amp UDB upgrade project.
I am trying to populate my boards bought last year.
I used this thread as reference:
I suppose I could create a spice model and compare the values, but was wondering if anyone has the definitive BOM?
Also, has anyone used anything that is not a 6CG7? They are not the most common option in Europe. ECC804 (6/30L2) looks similar on paper (mu 18 instead of 20) and I have those, but interested if anything else has been tried.
I used this thread as reference:
Tubelab Universal Driver Board, 2015 version
There are a lot of significant differences between the BOM on that thread and the one on this. E.g. R6/R7, 43K here, 150K on the other thread, R17/R18, 20K here, 68K on the other thread.I suppose I could create a spice model and compare the values, but was wondering if anyone has the definitive BOM?
Also, has anyone used anything that is not a 6CG7? They are not the most common option in Europe. ECC804 (6/30L2) looks similar on paper (mu 18 instead of 20) and I have those, but interested if anything else has been tried.
As noted in the BOM, selection of R6/R7 and R17/R18 will depend on HT and tube choice. Whether you're using anode to anode feedback (2nd stage to first stage or outputs to first or second stage) will have an impact too.
I did a lot of simulation and testing a few years ago. I ended up going with the original 150k and 24k with 500V HT and no anode to anode feedback. I have no problem using 12dB or so of GNFB.
I did some simulations with 6GU7s but the 6CG7s are easy to order online from the US so went with those.
I did a lot of simulation and testing a few years ago. I ended up going with the original 150k and 24k with 500V HT and no anode to anode feedback. I have no problem using 12dB or so of GNFB.
I did some simulations with 6GU7s but the 6CG7s are easy to order online from the US so went with those.
I should have read the disclaimer in the other thread ...
I need to look more closely at my project. I will be driving two UNSET Power Heads in PP, with 25CD6GB outputs.
Been there, built that.
Driving an UNSET Power Head in PP works great, but you will need to leave some parts off the driver board build. The UDB has a mosfet follower for driving the grid of the output tubes and providing adjustable bias. The UNSET Power Head (UPH) board also has a mosfet follower to drive the cathode of the output tubes with its own bias adjustment. You don't need both, and the cathode must be driven in UNSET, so the mosfet follower and associated parts can be omitted on the UDB build.
I have the setup seen in the picture still on the bench. Some parts like the OPT's and one driver board have been removed for some serious high power testing (over 500 watts from 4 X 26HU5's). I should be able to put one channel back together pretty quickly. I have lots of 25DN6 tubes here which are similar and have the same pinout. I probably have some 6CD6's in storage too.
If you tell me how much B+ you plan to run, and your OPT impedance, I can mock this up pretty quickly.
