Hi Folks,
Anybody try BH EL34 output transformer with Cathode FB connection? And not sure which parts need to modify when using CFB coonection?
TTG-CFB5000PP - Tube output CFB transformer [5kOhm] Cathode Feedback Push-pull - Shop Toroidy.pl
Anybody try BH EL34 output transformer with Cathode FB connection? And not sure which parts need to modify when using CFB coonection?
TTG-CFB5000PP - Tube output CFB transformer [5kOhm] Cathode Feedback Push-pull - Shop Toroidy.pl
Just consider that when using CFB OT you need to add 10% of the anode swing to g1's swing. On a BHEL34 is around 80 to 90 Vpp on top of the usual swing (around 70Vpp) to drive them. That's more than twice what would be normally needed.
For this project I'd stick with UL+"Shade", but I'm working on an "upgrade" of the BH for the cases when more swing is needed. It will take some time, but I hope to come with some good results.
For this project I'd stick with UL+"Shade", but I'm working on an "upgrade" of the BH for the cases when more swing is needed. It will take some time, but I hope to come with some good results.
Hey Zintolo, all of my build is in this thread. Just search for posts with my username. Both of my builds are the MK2 Rev 1.5 schema, both for the PSU and the boards. My 2nd build has a few tweaks we all discussed in spring of 2020.
Search for posts from gingertube, especially his posts from March/April/May/June of 2020. That's where all my minor mods came from. It's probably worthwhile to go back to around March 2020 in the thread and just read it through.
There is a tremendous amount of info in this thread, I know it's difficult to go back through and read it all. But it's what we've all done. I've probably read this entire thread all the way through at least 3-4 times. And if you want a historical understanding of how all this got to where it is now, you also need to go read the EL84 thread.
gabo
Thanks Gabo,
thanks for your reply. Gingertube has never built a KT88 version AFAIK, but a KT77 that IMHE is way more linear in UL and easy to drive compared to the KT88. I've seen very linear curves of the KT88 with just 10% a-g1 feedback (SpreadSpectrum posted them), that is around 10k instead of 39k shown on the original schematic (this would simplify the phase splitter job as well, because it will see an higher impedance. Here we have UL as well to lower the DF and linearize the curves of the tube, that's why I was asking you how you set the amp for KT88, as many of us personalized the project: EG Bfpca uses a 6k6 Raa at 400V B+, but tested it at 450 and 500V as well.
I will run three parallel tests with the simple BH schematic (different UL tap, a-g1 feedback ratio and phase inverter's plate load), an hybrid cascoded schematic, and an hybrid cascoded plus UNSET-CORONA kind of a-g1 feedback, in order to see how I do prefer it. I'll report the results.
Roberto
thanks for your reply. Gingertube has never built a KT88 version AFAIK, but a KT77 that IMHE is way more linear in UL and easy to drive compared to the KT88. I've seen very linear curves of the KT88 with just 10% a-g1 feedback (SpreadSpectrum posted them), that is around 10k instead of 39k shown on the original schematic (this would simplify the phase splitter job as well, because it will see an higher impedance. Here we have UL as well to lower the DF and linearize the curves of the tube, that's why I was asking you how you set the amp for KT88, as many of us personalized the project: EG Bfpca uses a 6k6 Raa at 400V B+, but tested it at 450 and 500V as well.
I will run three parallel tests with the simple BH schematic (different UL tap, a-g1 feedback ratio and phase inverter's plate load), an hybrid cascoded schematic, and an hybrid cascoded plus UNSET-CORONA kind of a-g1 feedback, in order to see how I do prefer it. I'll report the results.
Roberto
Yes, improvements and customization is what it's all about in DIY.
I think you have a good approach going and it will be interesting to hear the results of your tests. If it all works out for the better, I might tweak a few parts in one of my amps.
There have been quite a few tweaks over the years, I think most of them improved things, so it's great that you're now carrying the torch to a better design. Keep up the good work.
Thanks, gabo
I think you have a good approach going and it will be interesting to hear the results of your tests. If it all works out for the better, I might tweak a few parts in one of my amps.
There have been quite a few tweaks over the years, I think most of them improved things, so it's great that you're now carrying the torch to a better design. Keep up the good work.
Thanks, gabo
They will work fine, but most probably you won't have space to top mount it, so you need to bottom mount it. Pay attention to the pinout!
Almost all octal based pentodes have been covered here and things have been repeated many times, but still most information are vague.
I've 10 pcbs (5 pairs) and I will populate 2 pairs (for 6V6 and EL34), whilst for KT88 I will use two options based on UNSET and RCA50W amp.
I've working on an updated BOM with most of the known upgrades, some useful new ones and values adapted for different tubes (EL34, KT77, 6CA7, 6L6GC, 6V6GT, 6550, KT88, etc...).
Of course a second look at them by someone else, when I'll post them, would be useful.
I have a pair of EL34 BH GB PCBs I can send you for what I paid for them plus shipping. Also 2 power supply boards and 4 of the STU9HN65M2 MOSFETs.
It's going to be a long time before I complete the EL84 amps (PCBs are waiting to be tested and I have the transformers but then there's the metalwork to be designed and laser cut) and with lots of projects for other people I can't see my getting around to building the EL34 amps for years. Then again there's the question of how many amps one person needs.
Please send me a message if you are interested.
I have a few questions I was hoping someone could answer for me.
Are the documents in the first few posts still the go-to ones for this design?
At this point in time is it up to the person wanting to build this to use the schematic in the first post to have their own PCB's made up?
If the first post is not the one containing the most up to date files for schematics, parts etc; could someone be so kind as to point me to the latest and greatest?
Thanks, James
Are the documents in the first few posts still the go-to ones for this design?
At this point in time is it up to the person wanting to build this to use the schematic in the first post to have their own PCB's made up?
If the first post is not the one containing the most up to date files for schematics, parts etc; could someone be so kind as to point me to the latest and greatest?
Thanks, James
If it were me, I would still build the MK2 Rev 1.5 version and maybe tweak a few components based on the discussions after that time. I think the first post of this version is here:
EL34 Baby Huey Amplifier
This also requires the MK2 rev 1.5 power supply.
The version in the first post still had the power supply components on the channel boards. However, there were many people who got great results from that version, so it would be ok to build.
Maybe someone here can come up with some boards for the MK2 1.5 version. Or there might even be enough new interest for a group buy. Contact Prasi and see if he has anything available or there might be someone here who has some spare boards.
If not, I think all the files to make boards are in this thread or Prasi might be able to supply you with the files.
I have built two of the MK2, 1.5 versions and am very happy with the performance. I'm using KT88s for both of my amps. I realize there has been some recent discussions of optimizing the design for KT88s, but I'm very happy with mine and switching to EL34, KT77, or a variety of other tubes is easy. Just rebias for the specs of whatever you install.
gabo
EL34 Baby Huey Amplifier
This also requires the MK2 rev 1.5 power supply.
The version in the first post still had the power supply components on the channel boards. However, there were many people who got great results from that version, so it would be ok to build.
Maybe someone here can come up with some boards for the MK2 1.5 version. Or there might even be enough new interest for a group buy. Contact Prasi and see if he has anything available or there might be someone here who has some spare boards.
If not, I think all the files to make boards are in this thread or Prasi might be able to supply you with the files.
I have built two of the MK2, 1.5 versions and am very happy with the performance. I'm using KT88s for both of my amps. I realize there has been some recent discussions of optimizing the design for KT88s, but I'm very happy with mine and switching to EL34, KT77, or a variety of other tubes is easy. Just rebias for the specs of whatever you install.
gabo