Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: lkrasner on January 07, 2015, 02:31:45 pm
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I'm building a single ended amp in which I plan to parallel an EL34 and octal tube, with separate volume controls for each, so you can blend them how you want. My concern is with voltages. Normally I would run the octals with a plate voltage at around 375V, with a bit less to supply the screen. This is well beyond the safe point for the EL84, which should probably be around 250-300V. Is it a problem to run the octals at this range in terms of tone? Or is there any thing special I should to do handle it?
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I think you can run el84 tubes also at a little higher voltage
but it is also my opinion that you can run 6v6 tube at the "standard" el84 level without losing anything
if you want to limit the B+ voltage around 300v may be you can parallel a 6aq5 tube to the el84 and get anyway satisfaction
K
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What about screen voltage/ resistors. Is there any issue there?
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... EL84, which should probably be around 250-300V. Is it a problem to run the octals at this range in terms of tone?
Sure, why not just run the EL34 at 300v? Or even 250v?
You'll get less output power, but you'll also have a smaller bias voltage, meaning you'll drive to EL34 to distortion sooner (meaning less output power).
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I have a single ended amp originally designed for an EL84 (AX84.com High Octane). I modified it to add an octal socket. I only use one socket at a time but there's no issue at all running my octal power tubes at lower voltages. I didn't even change the cathode bias. Have done this for years. I never thought of blending the two sockets but it would be very easy. I'm not a big fan of EL84's so that's not an issue.