kevin gilmore 1,313 Report post Posted November 12, 2017 (edited) So I've been looking at a bunch of tube/solid state hybrid dynamic amp schematics, and every one of them is some form of bad, or really bad. (one person/ex company in particular) Low voltage plate, capacitve coupling of a high impedance source into a low impedance, poor balance etc. There had to be a better way. true balanced input. dc coupling. low impedance output. no feedback. proper use of a tube (pure transconducance) etc so I came up with this, work in progress. 4 x 3 inches ubaltobaltubeschem.PDF Edited November 14, 2017 by kevin gilmore 13 Share this post Link to post Share on other sites
spritzer 2,333 Report post Posted November 12, 2017 Odd that a proper Dc coupled input is possible... I wonder if Cavalli would complain about the lack of mosfets... 1 Share this post Link to post Share on other sites
kevin gilmore 1,313 Report post Posted November 12, 2017 (edited) board files for you updated including 100v massive overkill power supply ubaltobaltube.zip grhv100v.zip Edited November 14, 2017 by kevin gilmore 1 Share this post Link to post Share on other sites
JimL 296 Report post Posted November 13, 2017 (edited) Looks a lot like the front end of an electrostatic headphone amp (T8000-ish), but with relatively low voltage transistors (except for the KSA1156). You could always substitute a MOSFET current source for the input tube tail CCS. Edited November 13, 2017 by JimL 1 Share this post Link to post Share on other sites
kevin gilmore 1,313 Report post Posted November 19, 2017 there are now 2 versions of this, one with the tube on the component side, and the other on the back side for mounting megatron style. ask first. Share this post Link to post Share on other sites
joehpj 126 Report post Posted January 9, 2018 (edited) If I am going to drive high independence headphones with this, what should I do? 1) add triple darlington stage like tubehybrid/CFA did 2) add paralleled darlington stage like dynahi Edited January 9, 2018 by joehpj Share this post Link to post Share on other sites
kevin gilmore 1,313 Report post Posted January 9, 2018 so you add a volume control, then 4 of whatever flavor amps you like. Share this post Link to post Share on other sites
mwl168 577 Report post Posted January 11, 2018 Why does the PSU have two sets of F+/F- output? Share this post Link to post Share on other sites
cspirou 97 Report post Posted January 11, 2018 2 hours ago, mwl168 said: Why does the PSU have two sets of F+/F- output? There's one tube per channel. So one set of heaters per tube Share this post Link to post Share on other sites
mwl168 577 Report post Posted January 11, 2018 But there is only one output for B+ on the PSU? Share this post Link to post Share on other sites
cspirou 97 Report post Posted January 12, 2018 The filaments don't come from a common source, each has their own regulator. This makes sense because filaments require a lot of current. B+ is pretty low current so just one for both channels should be fine. Share this post Link to post Share on other sites
mwl168 577 Report post Posted January 13, 2018 That makes sense. Thanks! Share this post Link to post Share on other sites
mwl168 577 Report post Posted January 16, 2018 Has anyone built this tube unbal/bal board yet? 1 Share this post Link to post Share on other sites
luvdunhill 2,644 Report post Posted January 16, 2018 I am curious as well - what sort of voltage can it swing into what sort of load at what sort of distortion? Share this post Link to post Share on other sites
masamoto 10 Report post Posted July 10, 2018 Since this is probably the first thing I will try from the group buy I wondered about the transformer and the VA. Looking at the input ac like this would couple 2 cheap transformers work? The +-15 is from a GRLV or something I guess or would a LM317+LM337 do the job? Share this post Link to post Share on other sites
penmarker 10 Report post Posted July 29, 2018 Gonna build this from the group buy soon, On the board the silkscreen says "tube mounts on the back side of the board" but tracing the boards shows it's the same version as the one in first post. So tubes should be mounted from the top? I also have never built tube amps so I might be wrong. some questions I have: 1. How hot is the mosfet on PSU will be? Will heatsinking with chassis floor (3mm aluminum) suffice or does it need heatsink? 2. LT1085 require heatsinks or not? 3. Will it make a good preamp? Do I need to watch/match it's output impedance to the amp's input? 4. How to bias it? Share this post Link to post Share on other sites
kevin gilmore 1,313 Report post Posted July 29, 2018 (edited) here are both of them, not sure which one was in the group buy 3) Its a current mirror. So output voltage depends on impedance, currently 1100 ohms. Needs an output buffer if you are going to use it for a preamp. Edited July 29, 2018 by kevin gilmore 1 Share this post Link to post Share on other sites
penmarker 10 Report post Posted July 29, 2018 The group buy is the first one, cool that means it's the correct version. I was counting the tube pinouts counter clockwise. I'll try looking for a suitable buffer stage. Share this post Link to post Share on other sites
penmarker 10 Report post Posted August 25, 2018 I've compiled a BOM from Digikey for the supplied GRHV based on my silkscreen from the recent group buy board. I hope others can help check if I missed anything. https://docs.google.com/spreadsheets/d/1XMu81oWk6E3mXPW6ahhEuvmhg4U497F5I5W6JPQgnNo/edit?usp=sharing You might notice there's RES 90.9K and RES 1.10K, these are because I can't find 92K resistors sold without MOQ. Share this post Link to post Share on other sites
sbelyo 266 Report post Posted September 25, 2018 On 7/29/2018 at 9:29 AM, kevin gilmore said: here are both of them, not sure which one was in the group buy 3) Its a current mirror. So output voltage depends on impedance, currently 1100 ohms. Needs an output buffer if you are going to use it for a preamp. Kevin, can I use the Diamond output buffer ver. 2.0 ? Share this post Link to post Share on other sites
kevin gilmore 1,313 Report post Posted September 25, 2018 sure Share this post Link to post Share on other sites
samsie 11 Report post Posted July 15, 2019 (edited) Dear Kevin, I find the heater power supply portion to be rather handy. Would you please cut the HV supply portion away so that I can use the heater power supply portion for mini T2 project? Thanks Sam On 11/13/2017 at 7:45 AM, kevin gilmore said: board files for you updated including 100v massive overkill power supply ubaltobaltube.zip grhv100v.zip Edited July 15, 2019 by samsie Share this post Link to post Share on other sites
masamoto 10 Report post Posted January 13 Did anyone finish one of these? Share this post Link to post Share on other sites
