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Tonal Characteristics of Half Power Mods
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 4/20/2003 1:43 PM |
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Deltablues |
Tonal Characteristics of Half Power Mods I understand what cathode bias sounds like (from owning a tweed amp). It gives you a more compressed tone with a slight roll off of the highs. But how does the "Pentode/Triode" method of reducing output affect the amps overall tone? |
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| 4/20/2003 1:28 PM |
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| KB |
It's not that much DB at all. The real change of course is dynamics and at the least in Triode it gets a little smoother. The biggest difference is changing to Triode an panning from PP to SE. I think Pentode has a little more grain to it. I like the smooth sound of TRIODE mode SE and FIXED bias. The way the amp topology is set up is how the tone is going to be. Switching from Pentode to Triode isn't going to change that tone in the very least., KB |
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| 4/20/2003 6:22 PM |
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| bob predaina | i agree, there's not a lot of difference dB-wise between triode and pentode modes -- certainly not enough to consider it a half-power mod. the idea of the extra grids on a pentode is to provide more efficient clean power output than a triode. qualitatively, my description would be quite different. a pentode tube operated in triode mode will begin to clip sooner that it would in pentode mode. i wouldn't describe earlier breakup as "smoothness" -- in fact, i think of the distorted triode sounds as "harsher" with less headroom than the pentode equivalent, but that's why some of these audio terms are so nebulous. maybe the differences in our descriptions is attributable to the kinds of volumes that each of us like to play at. some of this is definitely related to whether you're operating PP or SE, and whether or not you're operating within the effective functional parameters of a NFB loop. as far as SE and fixed bias operation is concerned, i can definitely tell the difference between the tone of a pentode operated as a pentode or as a triode in that setting. |
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| 4/21/2003 5:43 AM |
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| steveR | Hey KB, My experience with the triode thing was bit different. I agreee that the output change was negligible, but I couldn't stand the tone of triode mode. Maybe I did something wrong or my configuration was particularly inapropriate for triode mode (4 6v6s in PP) but triode mode just made the amp sound like someone threw a heavy blanket over the top. Many people have described triode as "darker" but my experience was that it was kind of a muted tone, almost muffled. (Yes, the amp was cathode biased) I have the switch also in a SE el84 amp and the difference is roughly the same. I wound up replacing the triode/pentode switch in the 4x6v6 amp with a cathode/fixed bias switch which I find more useful particulary when in a band situation. However, being that I am a lover of learning and experimentation I would suggest to Deltablues that you try the switch. As with so many things, your mileage may vary. Also, if you are looking for things to try for alternative tone from the same amp, try mucking around with the NFB - a switch to change values, or disconnect altogether. cheers, steveR |
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| 4/21/2003 12:46 PM |
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| KB |
Yeah I'll agree with that and you'll notice a bigger difference of all the above at higher volume settings., KB | |
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| 4/25/2003 11:08 AM |
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| Deltablues |
This might be a dumb question, but is there any reason why you couldn't use both the cathode/fixed bias switch and a pentode/triode switch in the same amp? (e.g. are there any combinations of the two that wouldn't work together)? |
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| 4/25/2003 1:47 PM |
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| KB |
No, that's what my London Power has along with a pot that goes from SE to PP. Tone-wise the pot has more effect then both the switches put together but once again it's much more noticable at higher volumes., KB | |
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