QB2/250 amplifier

[flatheadmurre]

Some big boxes has been waiting to become an ampm for a long time now.



My original idea was triod driving triod connected.



I have some descent 5k irons so something in the 7-800v range was in mind.

Then Schade was brought in the picture by a friend and here i am.

What´s the way to go is Schade better then triode ?

It gives better power with triode like behavior but is it as good?

[GloBug]

Good thing I have my boner pants on.
I vote for schade, not for lack of power though.

[Jebem]

Nice Pentode tubesYou have there!
With those 4 tubes, I would build a nice stereo retro Push-Pull amplifier.

Kinkless tubes or beam power tubers as they call it (KT series) have appeared in the market as improved tetrode tubes that fixed the "kink" on the conventional tetrode tube transfer curves, fixing the linearity and power problems of tetrodes. Pentodes don't have that "kink" problem.

So a KT series tube have its virtues, specially now that the KT120 is out in the market, showing lots of power and good linearity, but a good pentode like the EL34 can make very musical amplifiers as well as long as You don't need too much output power.

As for triode tubes, I like them above all kind of tubes, in particular the 211 and 845. They are excellent as single-ended class A amplifiers if You can live with just 15 Watt of power.
Of course a Push-Pull class A amp with 845 tubes driven by 300B triodes transformer coupled (like the Marantz T1) is really hard to beat in sonic terms and retro style.

It all depends on one needs and tastes after all.

[flatheadmurre]

Ok so Shade is to be investigated.

For driver i have C3g or D3a at hand if you´re not suggesting anything else.

Anyone tried this one in shade configuration and at which working point ?

[radiostar]

Great audio tube, I prefer them triode strapped ...

I have many 813 tubes, but I've never seen those ones made by Philips.

813 DH Pentodes (QB2-250, 5C-100A, 4T100, U3, CV26, CV143, CV177)

813 VT-144 | Facebook

Good luck with project!!!

[flatheadmurre]

Philips made in France stamped on them.

[radiostar]

Made in RTC France factory for Philips

[flatheadmurre]

What i used to call an oversized rectifier tube is a good sizematch this time



Finally an amp to use a couple of 3B28 in

[hemgjord]

I've done some experiments with this tube in triode mode A2 SE. Sounds very good but I run them at 900-1000V with 10k load. I would guess that 5k would be OK at the lower voltage you are planning. However output resistance will be quite high with 5k, Ri in triode is close to 2k.

/Olof

[flatheadmurre]

I´ll always prefered high voltage over current so that´s a thing to think about.

I played around with it as SE and ended up with 1400v for triod strapped 10k.

I have to read up on schade and descide if that or triode is the way to go.

Still need more opinions on what sounds best to you people.