The Nemesis 813 PP Amplifier

[Paul Barker]

[Paul Barker]

I’m resisting, but anyway couldn’t afford the iron. I’ll be happy with a 60w Matrix.

[IslandPink]

What we need is an amp called the 'Iron Butterfly' !

[Cressy Snr]

What we need is an amp called the 'Iron Butterfly' !

My next amp is the calliopo-saxophio-trumparimba-claribasso-trombophone

[Paul Barker]

giggle

[JamesD]

Mark said...

What we need is an amp called the 'Iron Butterfly' !

so here we have https://inlowsound.weebly.com/iron-butt ... utput.html

[IslandPink]

D'Oh
Doesn't count, it's solid state ! ...

[Paul Barker]

I’ve forgotten exact figures but it’s about 600 plus watts. Try get an opt with the feedback to boot!

The distortion claims are amazingly low!

But it isn’t for me with no money. I’m making with what I have!

[ed]

D'Oh
Doesn't count, it's solid state ! ...

it really should count, it's prompted by Susan Parker, her of Zeus fame.

I think zeus was the very first mosfet amp I looked at, and maybe reponsible for my downhill plummet into all things fet.....

[izzy wizzy]

Not an iron butterfly but thought I'd post the final circuit before it went GM70

813psult.gif (9.66 KiB) Viewed 6287 times

Link to my Audio Website https://izzy-wizzy.com/?page_id=361

[JamesD]

I always admired the simplicity of your 813 ever since I saw it on Lynn's site - at the time I was building with the same topology using 6N6P and 2A3's - yours seemed brave and epic using 813s!

[izzy wizzy]

I always admired the simplicity of your 813 ever since I saw it on Lynn's site - at the time I was building with the same topology using 6N6P and 2A3's - yours seemed brave and epic using 813s!

Thanks but check this from Ian who built an amazing amplifier based on that design https://izzy-wizzy.com/?page_id=57#ian813

He got right what stumped me for years - DC fils.

[IslandPink]

James - can you think of any reason why I was able to get the Auroras dead quiet with AC fils on the 300B's, but Stephen couldn't get it anywhere good enough on the 813's ? There must be a few dB difference accounted for by the 10V vs. 5V , plus the Tannoy 15's vs. Ariels , but even so...
I think I used the Paremeko transformers which have 0 - 2.5 - 5 - 6.4v windings, hence a built-in centre tap.

[Paul Barker]

I’ve found same Mark, but I suppose there are exceptions.

[JamesD]

Ian's is a nice looking amp - not quite as heroic looking as your breadboard!

Mark: Its difficult to say as I've had amps that looked like they should have no hum be noisy and vice versa. Certainly higher voltage filaments are more susceptible to hum so the 10V of the 813 is going to be worse to get hum free than a 5V 300B. And if you run the filament from a centre tapped filament winding then for the 300B you are only 2.5V away from the earth ac wise and that also helps so I would predict that yours would be quieter but its not that simple.

What is happening with other winding's on the same core affects things and particularly if some of the winding's are ringing at mains frequency due to the rectifier switching exciting the coil... sometimes its mains radiation pick up by the heater wires - not as often as one would think though. The pick up of noise by the wires is often rf related and its rf carrying a mains related frequency envelop of noise that induces the mains related noise into the system and, again, as often as not due to rectifier circuit ringing at switching frequency. Its why I like to snub the secondaries of mains transformers and snub the chokes in the psu too...

You may remember the filament discussion Nick, you and I had some while back where we attempted to define a best practice way for connecting the filament of a dht to the heater supply and the signal circuit loop - I don't remember if we reached a definitive conclusion or not other than heating with an rf frequency supply looked promising providing the amp gain/bandwidth was stable at rf ...