Untapped Potential: Heath's W-5M
- Thread starter dcgillespie
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Thank- you so much for finding that error, Tim! I’ll get it corrected in just a little bit. Of course the 4 Ohm tap should be shown as grounded.
Dave
Dave
Poor Gilded Lily! ;-)
There's so much to absorb here, and, as usual, written in a way that even a non-technical person can understand. For just one example, I always wondered why S & S altered the decoupling arrangement in the power supply chain from the original Wliiamson. I assumed it was an error on their part, but now I see that the change was beneficial. I've always preferred the S & S version to the original, sonically speaking, and now I see perhaps why.
It's also interesting that, on the 16309 sample I sent you, someone wrote in marker, "8.6K". I thought maybe that was an error, but now I see that whoever sold it to me measured it correctly.
I'll be poring over this for weeks to come. ;-) And I'm very tempted to build an improved W-5 from scratch with the 16458's I have on hand.
There's so much to absorb here, and, as usual, written in a way that even a non-technical person can understand. For just one example, I always wondered why S & S altered the decoupling arrangement in the power supply chain from the original Wliiamson. I assumed it was an error on their part, but now I see that the change was beneficial. I've always preferred the S & S version to the original, sonically speaking, and now I see perhaps why.
It's also interesting that, on the 16309 sample I sent you, someone wrote in marker, "8.6K". I thought maybe that was an error, but now I see that whoever sold it to me measured it correctly.
I'll be poring over this for weeks to come. ;-) And I'm very tempted to build an improved W-5 from scratch with the 16458's I have on hand.
Thanks Zack -- Your lending me the transformers was instrumental in sussing out the 16309 transformer's capabilities, so again I thank you.
I thought the same think about the 16309's impedance marking, and was surprised when I found it to be (basically) the same thing.
This was one of those projects that's like pulling on a thread in a sweater. Every time I thought I was through, something else would come into question -- invariably from the last thing that came up when I thought I was through. So, you just keep pulling until there's nothing left to pull. I hope the thread lends some solid information to everything anybody wanted to know about the W-5. If you build the modified version, I think you will be well pleased with the return on your effort.
Dave
I thought the same think about the 16309's impedance marking, and was surprised when I found it to be (basically) the same thing.
This was one of those projects that's like pulling on a thread in a sweater. Every time I thought I was through, something else would come into question -- invariably from the last thing that came up when I thought I was through. So, you just keep pulling until there's nothing left to pull. I hope the thread lends some solid information to everything anybody wanted to know about the W-5. If you build the modified version, I think you will be well pleased with the return on your effort.
Dave
Maybe I missed any reference to it in the above discussion, as to whether this is a deliberate reference...
But, I think the title of this thread- "Untapped Potential"... is especially relevant- given that the output transformer primary is NO LONGER tapped.
Indeed, untapped, for even greater sonic potential...
And, I had to say- as I saw the posts describing the problem with the transformer taps- I said to myself "hey, are we about to see a conversion to cathode feedback?", even before I got to that point in the discussion. It's great to see that the transformer secondary winding characteristics were balanced and uniform enough, for this to work.
Regards,
Gordon.
But, I think the title of this thread- "Untapped Potential"... is especially relevant- given that the output transformer primary is NO LONGER tapped.
Indeed, untapped, for even greater sonic potential...
And, I had to say- as I saw the posts describing the problem with the transformer taps- I said to myself "hey, are we about to see a conversion to cathode feedback?", even before I got to that point in the discussion. It's great to see that the transformer secondary winding characteristics were balanced and uniform enough, for this to work.
Regards,
Gordon.
Glad you caught the reference to the solution in the title Gordon. It was deliberately made indeed!
Dave
Dave
Question on the schematic: It's not clear to me where the 315 volt screen supply comes from.
There ya go causing problems by finding errors! 
I'll get that corrected later on today -- Thank-you!
Dave
I'll get that corrected later on today -- Thank-you!Dave
There ya go causing problems by finding errors!
Dave
LOL! Okay, thanks. I was feeling kinda dumb... ;-)
OK. I think all the ghosts are eliminated from the schematics now. Thanks to Tim and Zack for spotting them!
Dave
Dave
Ah, some little solid-state bits! I'm not very good with those but I'm willing to give it a try. ;-) I can't see it in your photo. Does the mosfet need a heat-sink?
Nicely done Dave. Issues well thought through, with a clear write up of how this story played out, as usual!
Interesting read about why no EFB-controlled grid bias was necessary in this build.
Well, one solid state bit--a mosfet. That mosfet provides a low impedance voltage dropping capability to power the screens. It's the "high voltage half" of Dave's EFB regulator. It does need to be heat sunk. (Note the four diagonal parallel lines off the top right of the mosfet symbol in the schematic.) I suspect Dave will say you can attach that mosfet to a cool place on the chassis itself as long as you ensure the back plane of the mosfet is insulated. I suspect the part Dave noted for the mosfet is a plastic encased part number so self-insulating.
I have sometimes used over sized aluminum heat sinks for TO-220 style transistors in my implementations of EFB and it has worked quite well also, but that requires you to use a piece of perforation board on which to build the EFB circuit and to mount the heatsink itself, and then you mount the perf board to the chassis.
Interesting read about why no EFB-controlled grid bias was necessary in this build.
Well, one solid state bit--a mosfet. That mosfet provides a low impedance voltage dropping capability to power the screens. It's the "high voltage half" of Dave's EFB regulator. It does need to be heat sunk. (Note the four diagonal parallel lines off the top right of the mosfet symbol in the schematic.) I suspect Dave will say you can attach that mosfet to a cool place on the chassis itself as long as you ensure the back plane of the mosfet is insulated. I suspect the part Dave noted for the mosfet is a plastic encased part number so self-insulating.
I have sometimes used over sized aluminum heat sinks for TO-220 style transistors in my implementations of EFB and it has worked quite well also, but that requires you to use a piece of perforation board on which to build the EFB circuit and to mount the heatsink itself, and then you mount the perf board to the chassis.
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In the underside pic, it is mounted by a nut and bolt through the center mount hole of the choke at the top right of the pic. The 1K gate resistor is soldered directly to the gate terminal, and then a green wire to the other side of the resistor. A red wire is soldered to the drain terminal, and a black wire to the source terminal. Then the terminals are covered with heat shrink and the MOSFET is mounted with a dab of silicone grease. At the other end of the leads, the red drain lead connects to the 4.7K resistor, the green gate lead to the voltage divider, and the black source lead to the screens. There ya go!
Thanks for the kind words kward and yep, it’s a plastic device, so easy-peasy!
trobbins
Super Member
I'm a fan of 'belts and braces' power FET gate protection so had a second look at the EFB™ Screen Grid Regulator schematic. A quick check showed your SA-100 inclusion of that circuit included a 12V zener, which appeased my fault scenario mitigation demons. Did you intentionally eliminate the 12V zener with this project?
http://www.audiokarma.org/forums/in...-clone-in-progress.466229/page-4#post-6175273)
Ciao, Tim
http://www.audiokarma.org/forums/in...-clone-in-progress.466229/page-4#post-6175273)
Ciao, Tim
I see it now, thanks. That part appears to be obsolete. Can you recommend a substitute?
Hi Tim -- I eliminated the Zener because the recommended device has internal protection built into it making the external Zener unnecessary. As for it being obsolete now, I'll look around Zack -- I'm sure there's a suitable replacement out there.
Dave
Dave
Zack -- I see that the original device is still available at various part houses, but if you'd rather go with an in production piece, the STF12NK60Z is an even more robust piece in the same package, and also includes the back-to-back internal Zeners that the previous piece includes, so external protection is unnecessary with it as well, making it is a direct replacement for the original piece.
I hope this helps!
Dave
I hope this helps!
Dave
