X-Admin: news@aol.com From: larrysb@aol.com (nuke) Newsgroups: alt.guitar.amps Date: 21 Jun 2002 19:49:44 GMT References: <3d131601.260890154@news.freeserve.net> Organization: AOL http://www.aol.com Subject: Re: Amps with 2x EL84 vs. 2x 6V6's - sound/tone difference Message-ID: <20020621154944.19102.00000279@mb-ch.aol.com> Xref: newsstand.cit.cornell.edu alt.guitar.amps:394897 EL84 Gm = 11300 uMhos, Pdiss = 12W, g1 C = 10.1 pf, Rp 40k EL84 is a pentode with a wire wound suppressor grid. As such, the harmonic distortion contains considerable content in the 3rd and 5th harmonic due to the kink in the plate curves from the weaker performance of the suppressor grid vs. a beam forming plate. 6V6 Gm = 4100 uMhos, Pdiss = 14W, g1 C = 9 pf, Rp 50k 6V6 is a beam power tetrode. Beam power tetrodes generally exhibit better plate curves than power pentodes and have distortion spectra similar to triodes with most content in the second and third harmonic. However the small geometry of the 6V6 negates this to some extent and somewhat stronger third harmonic and some content in the fifth harmonic is to be expected over other beam power tubes. In other comparisons, the EL84 has a high Gm, which means that the peak grid signal can be a lot smaller than with the 6v6 with it's lower transconductance. This will obviously influence the design of the preceding stages considerably. Attention to the driver stage is of particular importance to avoid blocking distortion in EL84 based amplifier stages. Also particular concern must be shown with the placement of grid-stopper resistors to suppress parasitic oscillation in the EL84. (this is why the older VibroKing had so much trouble with the EL84 in the reverb driver and it was replaced with a 6V6 in later production). The EL84 was designed to produce moderate power levels on low plate voltages under 300v and occupy smaller space. This was of particular interest in europe since designers of consumer electronic equipment could potentially forego the power transformer and simply rectify the mains voltage to provide suitable power. The high transconductance factor simplifies the design of driver stages and offers convenient self-biasing (cathode biased) operation. The drawbacks are the EL84's shorter life span and higher distortion. The low cost of the tube tends to offset the life issue to some degree. Because of the supressor grid, this tube must be operated in or nearer to "class a" as the plate curves tend to become more nonlinear as cutoff is approached. The 6V6 can produce somewhat more power and is generally a long-life tube. The lower gm makes cathode biasing less appealing and the driver stages need to produce a greater signal voltage for the same power. It also requires somewhat greater plate voltage (but less power wasted in the screens) to produce the same power and occupies more space. The 6V6 produces substantially less distortion in the higher order spectra. It need not be operated at very high current levels to achieve low-distortion output, as plate operation is relatively stable closer to cutoff. Both tubes operate well into similar loads, the 6V6 tending to have an edge into lower impedance loads in my experience. However, one cannot infer a particular "sound" on either tube. This is a matter of how the designer chose to use, ignore or abuse the particular tube characteristics in each circuit. Each tube has characteristics that can be exploited to good advantage if applied in the correct manner, hence the AC/15/30 and the Fender Deluxii. One should not atrribute the sound of the amplifier to the particular output tube employed. It's only one part of the whole > >I heard someone say that a 20w amp with two EL34's sounds better than >amps with two 6v6's. Does anyone agree or disagree? Those of you who >are familiar with the differences... what are the differences in tone >and sound? Are they significant? Can you describe them? > >I already own a a Laney AOR Pro-Tube 1x12 20w Combo with two 6V6s >I am thinking of also getting a Marshall JCM-2000 DSL 201(two EL84's) > >thanks... > >Alan -- Dr. Nuketopia Spam filtering is off. AO-Hell catches most of it now.