VTL Tetrode/Triode

I had this same swith on a pair of Manley's 120Deluxe Mono amps, and after trying to just stick to one position (including the variable feedback option), I ended up using that unique future depending of the kind of music.

Fernando

Eldartford: I was prompted to do further research by this question of tetrode vs. pentode catagorization. What I noticed is that beam-tetrodes, lacking the suppressor screen of a true pentode, but with the beam-forming plates (which are not electrically-connected elements of the tube, otherwise known as electrodes) between the cathode, grid, and screen on the emission side and the anode (plate) on the collection side, are nevertheless often described as pentodes or 'beam-pentodes' - even in their original manufacturer's technical description papers. This finding, though I don't know the explanation for it, does help me understand why I've seen certain popular audio output tubes variously refered to as both tetrodes and pentodes in magazine reviews and the like. (Here is a page showing helpful diagrams of the differences.)

I also had forgotten that the British "KT" designation in fact stands for Kinkless Tetrode (duh!) - in other words, beam design. So obviously my KT-88EH's do not have an unused electrode element when run in tetrode in my VTLs, and the same would go for 6550's. Further confusing matters (for me) was the fact that my previous tubed audio amplifier used EL-34's (a true pentode) but ran them in ultralinear connection. The RCA 6L6 was apparently the first production beam-tetrode - see this link for the backstory. Though both suppressor screens and beam-formation plates are intended to deal with secondary emission from the anode, it does seem likely to me, as possibly alluded to in the article I linked in my post of 12/7, that the two constructions might behave somewhat differently when triode-connected.

Update: Tetrode/triode mode appears to be speaker dependent, too. I recently switched to B&W N802s from N803s, and with the Nautilus 802s, I'm back to tetrode for most of the time. Those babies like power, and triode is fine only if the dynamic swings in the musical fabric aren't too pronounced. Tetrode gives a much deeper and wider soundstage, and preserves all of the waveform; which makes for an unflappable presentation.

Well, anyway, I thought I'd post this, I'm just glad VTL provides both modes. With other speakers, it will be different, no doubt.

Larger woofers to control at the least, and maybe a more difficult impedance, I don't know. The 802 was always my favorite B&W, over the 801, although I haven't really auditioned the N-series. But I never heard one with tubes. Your experience is another bit of evidence suggesting that where tetrode is superior, the extra power may be the main or even the only reason.

Agreed with Hgabert post entirely, in a way the Triode/pentode switch could be a Hi-End Equalizer for audio setups.

Fernando