2x8w SET choice.

[Brett]

Originally posted by serengetiplains
Here's a quote from an email from John Broskie of TubeCAD re many-// EL84:

I have long maintained that a tube amp (SE or PP) that used 20 EL84s would probably be the best sounding amp on earth. The big qualification is that the amp would not be stupidly compromised in design: insufficient idle current or driver current (remember, it takes current to charge capacitance).

I have boxes and boxes of EL84's and this sounds just extreme enough to be fun.

[tube-lover]

Hi Geirw,

iS the tube 6C33 SE 15 watts output which use one 6SN7 per channel & running in 200V DC will be one of your choice!!
I recently build one of this amp. Sound very good & may be the reason was I use old tango XE-20-600s winding method.


thx

thomas

[GeirW]

Gday.

6C33 SE 15 watts output which use one 6SN7 per channel & running in 200V

15/200. sounds very interesting, do you have a schematic,
or link.

[tube-lover]

yes,

I use circuit maker to prepare the schematic.
Give me a little bit of time.

thx

thomas

[serengetiplains]

Originally posted by GeirW
15/200. sounds very interesting, do you have a schematic,
or link.

Here's one for you: 1 and 2. Note the coupling method, which biases the output tube by means of the voltage difference appearing across the anode resistor of the driver stage. The benefits of this topology are: 1) no cathode resistor (or resistor+capacitor) in the output tube (= better energy transfer to the speaker + better damping + less distortion etc), 2) no coupling capacitor or transformer between driver and output (= reduced grunge + phase shift etc), and 3) driver supply grunge typically amplified by the output tube of a single-ended circuit (ie, as fed to the output tube grid only) is partly cancelled by being coupled in-phase to the output grid *and* cathode.

Here's my take on benefit 3. Of the few advantages push-pull circuits hold over single ended, one of more significant is the inherent cancellation of power supply noise when a push pull stage is fed by one power supply. Assume, on such stage, the power supply voltage goes down slightly (ie, the supply responds to a momentary high current draw and supply voltage drops on supply impedance). That momentary PSU voltage dip appears on the plates of both tubes in the stage in question (not so bad on the relative scale of dip voltage as a percent of overall supply voltage) and is coupled to the grid of the next stage (bad on the relative scale of dip voltage as a percent signal voltage). But because the voltage dip appears in the same phase on both tubes, which are amplifying the signal 180 degrees out of phase, the dip effectively cancels as a source of noise.

Noise cancels as such, and completely, only when both tubes of a push-pull circuit are precisely balanced. No two tubes achieve perfect balance, statically or dynamically, leading to imperfect noise cancellation the degree of which bounces around like a bucking horse: don't no one know where it will go next. I consider this important because I suspect the ear is acutely sensitive to changes in distortion relative to frequency, phase and voltage level. Also, note the cost of attaining even the imperfect degree of noise cancellation a push-pull circuit attains: a significant increase in circuit complexity.

Compare noise cancellation on a push-pull circuit with noise cancellation on the single-ended circuit I posted above. In this latter, PSU noise cancels only partly---PSU noise voltage is reduced by passing through the anode/bias resistor and thus appears at differing voltages on the cathode and grid of the next stage---but the degree of cancellation does not bounce around, and is inherently more linear in phase, frequency and voltage level. Now, compare the complexity of a typical push-pull circuit with that of the circuit I posted. I can't imagine a simpler working circuit than the latter.

[argo]

Originally posted by Kuei Yang Wang
Konnichiwa,
...........

Or you could use an all EL84 Amplifier, 4pcs trioded EL84 in the output stage, loaded by 2K5 (or even 1K2) and another EL84 as driver. ........

Sayonara

Wang san and others

Do those paralleled tubes need to matched ? I have many EL84s but all from different year and production.

Cheers,

Argo

[tube-lover]

Hi,

pls see the circuit.

thx

thomas

[GeirW]

Gday.

,
having diffeculties locating 6C33 datasheet,
do you happen to know where.?

[serengetiplains]

Try this for a starter.

[moamps]

Originally posted by GeirW
....having diffeculties locating 6C33 datasheet,
do you happen to know where?

http://www.jogis-roehrenbude.de/Verstaerker/6C33C.htm