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You may want to add Mouser PN 293-47-RC or similar to the BOM.

The posted BOM has a 22 ohm resistor (NFB ) which is recommended for 2 way or full range speakers. The 47 ohm is recommended for three way speakers and or speakers that are difficult to drive.

Gregg,

Received my board yesterday. Nice board! Parts are on the way. I'm going to put it in this amp:



Happy New Year to all!!

http://s378.photobucket.com/albums/oo22 ... %20Boards/

Pictures of completed board

Looks great! Did you cut the heat sink in half and mount on each side? I will make a note in the BOM of the 47R.

Actually I used a Aavid Thermalloy PN 577202B00000G that carries a Digikey PN HS107-ND

It can be found from Mouser using PN 532-577202B00

It is actually a TO-220 heat sink that I used 2 of for each Fet

I found the BOM heat sink to be larger than what I wanted to see on the board. Either will work and I guess its a matter of personal taste. I felt that doubling up on the heatsinks would provide adequate cooling for the semiconductor. I had about 50 on hand. I used 4-40 hardware and didn't use a nonconductive insulator.

For those wishing to know the measurements they are as follows.

Height .750
width outside to outside .530
inside width .425
Front to back .500

As I built it
front to back 2 units 1.010

What lovely pics!

I'll add that tidbit to the docs when I update them, thanks!

Cheers!

Guess what's in?

For the NOVAL fans here

Pic, Docs

w00t!

For the standard ST70 feedback loop connected to the 16 ohm tap, Geek specified 1500 pf paralleled with 1k.

I am using an Edcor 6600 primary with only 8 ohm secondaries. In this case, the cap would be 1500 x 1.414 or 2200 pf? And the resistor would be 1k x .707 or 680 ohms?

Hi Tom,

That FB network depends totally on the output transformer and needs a scope and a 5KHz squarewave to choose.

My opinion is to leave that FB cap out for now.

Cheers!

Geek, stay with the feedback resistor you specified then?

So it will not change value, stays at 1k? Only change the value of the feedback cap as required? What is a good value to start with, the one you specified? Later I will ask how to "adjust" the feedback cap.

tomlang wrote:Geek, stay with the feedback resistor you specified then?

Yes.

So it will not change value, stays at 1k?

Correct.

Only change the value of the feedback cap as required?

Yes.

What is a good value to start with, the one you specified?

Yes.

Later I will ask how to "adjust" the feedback cap.

Not a problem :-)

It's actually pretty easy to do with the aforementioned equipment.

Some pics of a prelim layout using the Octal Board.

Lookin' great so far! :-)

I mounted the big transistor on the bottom and recessed the board.

Just be sure the GDS are in the right holes and no problem.

If you want to keep the sockets on the front you may not be able to clear the heatsinks. I am either going to plug the holes or, if the big transistors tend to getting too hot under the chassis, putting some kind of screen over the old socket holes.

Hey, a screen would be great as it'll create convection underneatth.

Also realize I am using 6bg6ga tubes and I am playing around with where to put bias pots and pin jacks for the meter probes (black) as well as pin jacks for the anode wires (red).

Cool!

I'm going to build another here and try TV tubes as well. I was given a pair of MK-III output iron for Christmas and look forward to making a monster version

Cheers!

Iron for Christmas! To some that would be like a lump of coal, lol.

So I started thinking about your noval version and why not use a 12bh7 instead of a 6cg7; it appears you thought of something like that by bringing the heater pins out separate!

Would, in fact, a 12bh7 be a reasonable try? How about a 12at7 in the 5751 position?

12AT7 can be tried, but it may need rebiasing on the 1.2K resistor to keep the anode voltage in spec.

I did try a 12BH7 and it need different current and require significant component changes. Also the gain will be a lot less.

Cheers!

Has anyone had the time yet to give this a good peer listening review?

Cheers!

Change of gears, now going with "regular" tubes in this and using original Dynaco output transformers (in hand) so stayed tuned very soon.