• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Ef86, 6n1p & 845pp

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Ef86, 6n1p & 845pp

Is there any "simple" 845PP schematics?
I built a KT88PP and I love his sound! :

Is it possible to build in a similar way an 845PP?
(BTW I have some spare SV83... so I could use them instead of the EF86)

Of course I'll be going to use higher B+...
Is it possible to use a "simple" power supply schematic?
I made several web search but they are all really complex (and heavy)
Thanks for your help!

Francesco Pennelli


Joined 2003
Paid Member
> I built a KT88PP and I love his sound!

So why would you want to fool around with an ancient tube, that needs about three times as much heater, plate, and drive power, to get similar output power?

> they are all really complex (and heavy)

That is WHY mainstream audio switched to tubes like 6L6 and 6550 and abandoned the big triodes: triodes are very wasteful and VERY expensive amplifiers.

Naked pentode amplifiers are nasty speaker drivers. That 6550PP UL design you point to runs the 6550s halfway between Triode and Pentode, which is a big improvement in musicality. You could also try disconnecting the screen grids from the transformer taps, and connecting them to the plates with 470 ohms 2 Watt resistors, for pure triode operation.
for an 845 pp you are way over 800V anode (most likely 1000-1100) to get a mere 80 W... you ll need 300Vpp (grid to grid) drive and a huge, fully insulated o/t.. not worth the fuss, unless you are deep into it.. otherwise i propose you tried fiddling around you kt88 pp .. try to tune the feedback for your own speaker to get a proper df.. what phase splitter are you using?...
what about psu?
the only simple enough 845 pp designs ive seen are with an interstage and another 845 driving the output pair.. plus the drive for the dricver 845.....
I wish to use a "classic" tube in a "not classic" way
You're right about the PP.
I'm going to try SET.
I was thinkng to use this drive:

It shouldn't have a problem to drive the 845 since it has 347Vp-p.
I was also thinking to get rid of the coupling cap using separate transformer (like in the Simplex by A. Polisois)


The company that made my KT88PP Power Supply can provide me with whatever kind of PS I want at the right price.
I can also have good 1500V MKP caps so that I could make a "simple" PS (with SS or VT diode).
Thanks for all the help you could provide.

Francesco Pennelli

PS. I'm not using feedback on my KT88PP...
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.