5879 Bassman/AC 15 mashup

[Ledzepp007]

Comments on the attached schematic? Will it work? THANKS!

[tubenit]

If you leave out his switching ideas very similar to Geezer's HoSo56 yet worth comparing and noting differences. 

I would recommend moving your 1.5k resistors (following the coupling caps after the LTPI) and put them on the grids of the EL84's.

I think the .047 cap after the 5879 may be too large?   

I would increase the .01 cap at the "bottom" of the LTPI near the NFB resistor to something more like .047 or .1

With respect, Tubenit

There is a layout for the HoSo56 both as the original layout and in a Hoffman layout board style here (you could just use whatever values you want in your schematic with this layout) :

 http://el34world.com/Forum/index.php?topic=6176.0

[tubenit]

Here is what I would consider to change.   The 220p "enhance cap" helps smooth out the high end harshness without losing the high end, IME.

I've found 125v to 140v on the plates of the 5879 to sound pretty good, IMO.  So, I'd shoot for that and change the dropping resistors as needed.

With respect, Tubenit

NOT sure about the NFB values either?  I might be inclined to change those also. 

[Ledzepp007]

That is EXTREMELY helpful. Thanks.

I’ll probably just build the Hoso as it’s close and it’s verified.

I ordered up some transformers from Mag Components and it looks like the AC15 style output transformer I ordered has a 6K primary impedance. I expected  8k. I wonder if this is an error. How bad would it screw things up if it is, in fact 6k?

[Ledzepp007]

Anybody try one of these with negative feedback? I imagine it can be a rather gainy amp

[tubenit]

I don't remember if anyone has built one with NFB?  I'd look up NFB on amps that use two EL84's and see what values they use.  Maybe try those and tweak values to your taste .......... OR put the NFB on a switch which is very easy to do.

I think I would try the NFB with 1.5k/33k-47k range  (instead of 100k).

With respect, Tubenit