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Any recommendations for EL84 tubes with good reliability and durability? I have a DC30 clone with tubes pulled from an old organ, and have had some recent issues with EL84s that started to hum. The amp has 350 volts on the plates, and I have it biased with a pair of 75 watt resistors - one 75 watt resistor per pair of output tubes. So, what are the good choices in EL84s? Shugaung, JJ, Russian or? I see a lot of Russian 6P14 type tubes on fleabay - EV, EB, ER - what's the difference?
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EL84s will take a real caning as far as plate voltages go. 350v is about average, but Traynor amps (for example) run them at much higher voltages and it's not uncommon to find them running them to 400v or above. I recently worked on a Marshall where they were running at 420v. They're more susceptible to failing through high screen voltage and it's important to know what your voltage is and to ensure that the screens are protected against excess dissipation through appropriate sized screen resistors.
I don't know what you mean by "biased with a pair of 75 watt resistors" - do you mean Ohms? The value is less important than the actual total tube dissipation.
For a DC30 my personal recommendation would be the Sovtek EL84M. Not an expensive tube but it is very robust and will take a lot of punishment. I like the sound of them in this particular amp too. -
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Pairs of EL84's running at 350 Vp are usually biased with 120 ohm or 130 ohm 10-15W resistor + a bypass cap...I suspect you are running them really hot. I've had great luck with JJ & EH EL84s as long as they've had a 24 hr burn in.Comment
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The DC30 has a half power switch that drops out two of the power tubes. In mine, it uses 150 ohms for the cathode bias for two tubes, and 75 ohms for four tubes, and the bypass cap. I tend to set up an amp with cold bias to save the tubes.Originally posted by Alexander View PostComment
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