Will work on a MK-4!

[TerrySmith]

I have a pair of nice MK-4's. Both were rebuilt with Curcio boards and cap-boards from tubes4pro. I was really disappointed in the Curcio upgrade, seemed to suck the life out of them.

This new Diy board will work with a few mods. It will need to be cut to fit, make a line thru C2. Drill 4 mtg holes. Stuff the right side, from the center of the 12AX7. Add a 47K resistor between J19 and J20. Make sure none of the traces contact the chassis. Lastly, wire in as normal.

Here's a couple of pictures.

http://www.diytube.com/forumpix/ST70_MKIV_1.jpg

http://www.diytube.com/forumpix/ST70_MKIV_2.jpg

[EWBrown]

I was wondering if one of these boards could be "chopped" for mono use,
I have tried a circuit similar to the Curcio driver, using SRPP 6N1P as the driver and a second 6N1P as a cathodyne (as in ST70) phase splitter, both as a single tube section, and as paralleled triodes with the P and K resistor values halved) and wasn't real excited with the results, not any better than the original 6AN8 or 7199 circuit design. I think the Modified Mullard is the way to go... I believe the MK3 and MK4 boards from Triode Electronics are closer to the Mullard design, in that they use an LTP splitter rather than "cathodyne"..

The cheeziest phase splitter I ever saw (or heard) was used on a Voice of Music (VM) console amplifier, the output from the preamp chassis (standard volume / balance / treble / bass design) fed straight into the grid of one of the 6V6s per channel. A sample of this signal is sent to a half a 12AX7 which acts as a unity gain inverting stage (plate resistor 47K, grid and cathode resistors 470K). the output from the 12AX7 plate is capacitor coupled to the other 6V6, and thusly something closely, but not quite fully, resembling a push-pull signal goes to the cheapo OPTs.

I just resuscitated one of these from the "crypt". It sounded, er, not too bad, but when I ran it against a DIY35, the difference was incredible, then the VM really sounded like what it was, a cheap-as-possible design. Yellow_Light_Colorz_PDT_07
The best part of it is the power trannie, 300-0-300 VAC, 150 mA, three independent 6.3 VAC filament windings, one 5VAC winding to light up the rectifier tube, and an isolated 120VAC, 850 mA winding, that originally fed power to the tuner chassis, or record changer (aka groove grinder mechanism).

But not all is lost... The power supply has everything just what I need for my 6EM7 PP amp, so it is going to get gutted except for the power supply section, and given a new life. THis also saves all the onerous chassis punching and drilling, as most everything that I need is already present.
I'll even use the 12AX7 socket for a simple "linestage" pre-driver stage if needed.

Yes, it will be a bit on the ugly side, as this chassis was meant to be mounted out of sight inside a pretty fancy console. But, I am sure that it will sound a LOT better Yellow_Light_Colorz_PDT_16

Followup:

The 6EM7 PP amp sounds great, using Triode "silver" Fender outputs which I bought last year, before the UL version was released. These have about 4X the iron and copper content of the original VM OPTs.

/ed B in NH

[Shannon Parks]

Hi Terry,

How does the width of the ST70 driver fit in your MKIV chassis? I'm looking at some under shots of a MKIV chassis and it looks like it will just fit (ie clearing the front of the chassis and the two EL34 sockets). Did you have to sand the boards down at all or use a shoe horn? Is there a little extra wiggle room?

I'm asking as I'm working on a universal MKIII/MKIV replacement driver and need it to fit in both units.

Reference Dimensions
The MKIII board is 3 3/8 inches wide.
The MKIV board is 2 7/8 inches.
The ST70 board is 3 1/4 inches.

Thanks!

Shannon

[TerrySmith]

All I did was cut to lenth and drill holes as necessary, and they fit nicely! I'm still amazed at the difference in sound, compared to the stock 7199 board and the "other" brand board.

Also, the MK-3 boards you cut & drilled fit perfect also. Hopefully I will have them up and running after the holidays. As far as the MK-3's, I was thinking of using a 6CG7 or 6GU7 as the PI, and building it with the Eiclone parts/circuit. Or should I use the ST-70 parts/circuit?

[Shannon Parks]

As far as the MK-3's, I was thinking of using a 6CG7 or 6GU7 as the PI, and building it with the Eiclone parts/circuit. Or should I use the ST-70 parts/circuit?

Hi Terry,

Yes, two cuts and a jumper will allow 6CG7/6GU7 usage. I am going to make this cut-n-jumper mod a hair easier on this universal driver layout (like silkscreen X's to mark the spot).

Here's the Mark III parts list I have thus far, with changes to:

- Increased the 100k 12AX7 plate resistor to 150k as we have a higher supply voltage with the result of better PSRR, linearity and gain.
- Changed the two coupling caps to 600V rated ones.
- Changed the grid resistors to 100k. I left the coupling cap value at .22uF which is exactly what the Pyramids in my test MKIII's measure. I fear increasing this cap could cause some occasional instability in the low frequencies.
- Raised the LTP plate resistors to 51k and lowered the LM334Z current set resistor to 12.1 ohms, once again since we have a much higher B+ supply. These values may get tweaked down the road. Basically, I don't want to see a voltage less than 10V at the PI's cathodes during idle.
Note: Don't make these mods to a ST70 board, folks!

Sorry that the reference designators are different for you, Terry. Yellow_Light_Colorz_PDT_19

Code: Select all

My Mouser Bill of Material Info

71-RN60D-F-1.0K 2
71-RN60D-F-475K 1
71-RN60D-F-100 1
71-RN60D-F-2.74K 1
71-RN65D-F-150K 1
71-RN60D-F-33.2K 1
71-RN55D-F-475K 1
71-RN55D-F-12.1 1
282-51K 2
71-RN60D-F-100K 2
71-RN55D-F-1M 1
72-T93YB-500K 1

75-715P600V0.1 1
80-CK05BX821K 1
80-CK05BX101K 1
75-715P600V0.22 2

511-LM334Z 1

[WA4SWJ]

Shannon,

OH NO! Another project to build!?!? Yellow_Light_Colorz_PDT_12

I have 3 Mark III new chassis (from eBay) that I'm waiting to build something on so I'm going to wait for your new board - if that's what you're telling us here. If so, sign me up for 3 !

Can't wait!

Regards,

[Shannon Parks]

Can you tell us a bit more about the upcoming Unidriver board?

Hi Wodgy & Ed,

The Unidriver will be a drop in replacement board for the Dynaco Mark III and Dynaco Mark IV monoblocks. It will also function as the new Ike driver with the power supply and bias duties done on a separate board, which is still in the early design phase. The Unidriver is basically 2/3s of the ST70 board design, with some small modifications. The Mark IV parts list will be identical to the ST70 one, with the changes in the Mark III being noted above.

The alpha boards will probably be ordered this week. I have a vintage set of Dyna Mark III's borrowed from my friend Francois which will be perfect for upgrading. I'm reforming the quad caps right now. Yellow_Light_Colorz_PDT_06

Shannon

[WA4SWJ]

Shannon,

Fantastic! Like I said, I'll take 3 when they are done. I've been using my eiclones for L-C-R home theater amps and my ST-35 for the surrounds. They work great and sound fabulous! However, I'd like something less "homebrew looking" for the main amps so that's why I bought those nice chrome clone chassis to build on.

Hopefully your new board will drive KT-88's to full power (probably will). I'm going to get some of those tubes for these Mark III clone amps I build. I have some new EH 6550's that I am thinking about putting into my eiclones since my SED EL-34's have a slight red glow in some areas of the plates with a 50mA bias setting. I haven't substituted the 6550's yet. I've got to get some more transformers on order too for the new amps!

Haven't decided yet if I'll use a tube or solid state rectifier. I could be persuaded either way I think. The Mark III chassis has the holes for tube rectification so that would be a bit nicer looking I guess. But I'd sure like to have more power supply "stiffness" for these forthcoming amps. I could design a solid state power supply board myself but I just don't have the time, so I'm leaning toward tube rectification as much for expediency and looks as anything else. It would be interesting to hear more of your ideas on power supplies and the impact of your approach versus tube rectification. I'm not real sure if I could tell the difference audibly.

BTW - my ST-70 with your board is also fantastic. It looks good too.

Keep 'em comin' and I'll keep building!!

Regards,

[TerrySmith]

Ed,
The SDS cap board that Uncle Ned sells will take diodes or tube rectifier.

[Shannon Parks]

Hopefully your new board will drive KT-88's to full power (probably will).

Hi Ed,

No problem at all! That is the beauty of the long tail pair phase splitter using the LM334Z as 450VDC of HT goes a long, long way. One more note I haven't mentioned, but should be semi-obvious: I want this board to be usable in any future Ikezilla amps.

Haven't decided yet if I'll use a tube or solid state rectifier. I could be persuaded either way I think. The Mark III chassis has the holes for tube rectification so that would be a bit nicer looking I guess. But I'd sure like to have more power supply "stiffness" for these forthcoming amps.

My opinion is to stay with the original power supply with the 5AR4. The Mark III (like the ST70) is just so well laid out underneath (ie clean) and easy to work on that it would be a shame to clutter it up with a cap board. That said, the SDS board is a good board in this application. You could wire it up to use either SS or 5AR4 and try both! Yellow_Light_Colorz_PDT_05

Shannon

[EWBrown]

I found with the "new made" MKIII chassis that are available on e-bay (the version w/o the multisection capacitor mounting hole punched) is that the Cyrus Chong cap board does fit insude, though rather tightly, but this does not allow one to use the supplied AC power switch, as the board is too close to the inside front of the chassis.

Either have to re-drill and relocate the power switch or just do without, and use an external power switch.

A less desirable "correction" would involve surgical modification of the cap board, and that isn't a really good approach...

/ed B in NH

[TomMcNally]

Here's an under chassis view of what an amp SHOULD look like. No wimpy electrolytics in this PS ! Yellow_Light_Colorz_PDT_19
Notice the big man-sized chokes ! No baby stuff here. haha 816 cubic inches of space !

[WA4SWJ]

Tom,

Show us the top too so we can see those man-sized tubes on top!

Regards,

[TomMcNally]

Just a lil pair of 300Bs ! Currently a nice 83 Mercury Vapor rectifier, with genuine Amperite Time Delay relay tube for warm up.