Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: NEjoe on April 08, 2011, 11:41:09 pm
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I've been trying to decide on the voltages for the plates and screens of a PP EL84 amp.
I've been searching about and the "sweet spot" as some people call it, is about 345 volts on the plate with the screens a few volts less (cathode at about 11.5 Volts).
The other thing I've run across is the high plate/low screen setup...like 400V plate and 320V screens, which might not be so great for tube longevity, but is supposed to sound good......
Is there a sweet spot for EL84s (in PP) under 300V? And where would you run the screens?
MMMMM....listening to Little Feat "All that you dream". I'm not after any particular tone, but that one wouldn't be bad :laugh: Yeah, probably not possible with EL84s, but I'm thinking more clean than crunch on this.
Thanks in advance for any insights.
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Just under 300V is considered to be one of the sweet spots for EL84s.
I really like how the AC30 / Rocket circuit runs them just under 300V with g2 at 3-5V less.
Looking back at my notes (Rocket PPP) I can see that I tried a range from 315V/303V downwards and settled on Plate 283V & g2 at 273, which is flying lower than most other folk do.
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I know that Bluesbear likes 300 or less on the plates. After much reading, I believe what's important is the wattage dissipation, regardless of plate voltage. I'm sure many with more knowledge than me will chime in as well. :smiley:
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That whole conversation confused the Hell out of me so I'll just go with what I know. The sweetest sounding EL-84 amp I've ever played is a Gibson GA-8t with 299V to the plate. There are obviously other ways to get "the tone" at higher voltages, but I don't know how so I see no need for me to switch. It's all subjective, anyway. I will blaspheme: I've never heard a Vox amp I like (only 3 or 4 in person). They've all sounded brassy and harsh to me. I much prefer warm and smooth. As I am in the minority with that, you should take everything I say on this subject with a large grain of salt. I just know what has worked for me in the past and what I want as the final result.
Dave
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And really in the end, that's what's most important (imo) ... what sounds best to you! My old amp sounds great to me with a cheapo Behringer reverb pedal in front of it. I would think maybe I just have poor ears ;) but other people think so too. Regardless, when I get the scratch I'm building Geezers HoSo amp... maybe when I can do side by side comparisons I'll think my old Harmony sounds like crap, who knows? :)
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I've never heard a Vox amp I like (only 3 or 4 in person). They've all sounded brassy and harsh to me. I much prefer warm and smooth.
Do you think that has to do with a Vox's tone stack? Isn't the treble pot and cap something like 47pF, 1M?
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"Do you think that has to do with a Vox's tone stack?"
Truthfully, I have no idea. I haven't really looked at them to know. The only EL84 amps I've found that really work for me are old Gibsons and the Tremolux 6G9. The Marshalls are okay but not my favorite. I don't hate the Vox's; they certainly worked for the Beatles. They're just not my style or choice for playing guitar.
Dave
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Why limit yourself to one (or two) parameter(s)? Besides plate and screen voltages, what about:
Pre-amp configuration - which harmonics are you aiming to amplify? And how much voltage swing and current are you using to drive the output tube grid(s).
Bias point
The reflected load
Amount of iron in the OT
Type of speaker
etc