833 Push Pull Design

[Miles Prower]

Hi Guys

Been reading this site for a while now on and off great site btw!

I need a design from top to bottom of a push pull amplifier using 2 833 tubes for each channel im trying to achieve 200wpc preferably mono blocks i know these involve a lot of high voltages and many people will try and talk me out of this please dont lol! the 833 tube is my tube of choice i will be using these mono blocks to power a pair of Kef Reference 4`s these cabs are rated at 400watts supposedly!? (and i understand valve power is different to solid state).

if anybody could point me in the right direction as to a complete DIY i will be very please .

A PP pair of 833s would be barely loping along at 200WPC. These can do more like 1500W, and at 200W, might not even get hot enough. The specs call for running them at red plate temps.

You could get 200W from an 833 SE amp.

If it's 200W you need, you'd be better off with the 814, as a PP pair of these can easily do 200W, and some more, and they don't cost the $BIGBUX either, not are the DC rail voltages outrageous. The only potential pitfall with this type is that it'll be running pretty deep into Class AB with a possible x-over distortion problem. Since its design was patterned after that of the 807, it also might require some extra help via lNFB to sound really good. The lNFB could be set up as cathode NFB. Easily done if you need a custom OPT since you can always specify a balanced secondary(ies) or feedback tertiaries.

Screen driven 6LW6s could also do 200W, but screen drive, especially to extreme power levels, presents its own set of problems, especially premature failure due to screen overheating during extreme clipping that can send the actual plate voltage negative, sending all the current to the screen. I'd prefer to run 'em a good deal more conservatively than that to get some 115W from a PP pair.

 

[Magz]

"I also found that adding an autoformer between the amps and the speakers (to raise the speakers' nominal impedance from ~3-4ohm to ~12-16ohm)made everything sound a whole lot better."

That sounds suspiciously like what I've heard before for OTL amplifiers. A huge initial effort to avoid an OT, then they find it sounds better when they put it through an autoformer. I assume that's because the bass got better with a lower output Z.

Everything got better, not just the bass. Better detail, better imaging, better soundstage depth. The system sounded good before, but now it sounds better than anything else I've ever heard. I can't think of one area where anything got worse, in fact!

 

[Magz]

There was an auto-former called the Zero several years ago that was marketed as an improvement for OTL's.

That's what I'm using, a Speltz Zero. I bought the "naked" versions and put them into nice little 7" x 7" x 3.25" black anodized Landfall chassis, with Cardas copper binding posts. Matches the amps very nicely, and the effect on the sound is just amazing. Highly recommended if you have a challenging speaker load!

 

[CV6045]

833A PP Amp

Not to depress you but what you are undertaking is a mammoth task. about 10 years ago I embarked on building a PP 833 Amp....long story short the project just kept getting bigger and bigger to the point where it finished up the size of a 3 bedroom house...joking a side it took over everything as all we think we know goes out of the window and when you are dealing in voltages above 1200 things change and it all takes on a life and demand of its own. Anyway good luck and dont be deterred....I am only voicing my opinion. If you want to see my circuit diagram that I designed then let me know and I will be happy to posit it here