I have a question about the B+ on an EL84 in single ended configuration. From most research I've done and the datasheet I determined that the max B+ should be about 275-300V, but then I saw tubemaster's schematic in this thread that uses a B+ of 350V. So I was hoping someone could give me some insight on what a proper B+ plus can safely be and how to determine it since datasheet values aren't always followed?
Thanks much
Thanks much
Hi,
The anode can take more than 300Vdc from most EL84s' manufacturers, the limitation is the screen voltage, most EL84's screen should not exceed 300Vdc with the exception of some Russian tubes such as 6P14 with military specs. To be on the safe side leave the anode at or below 300Vdc, if you operate the amp in UL or triode mode.
In my Chinese version of EL84 amp, it comes with 220Vac transformer when plugs into the 240Vac main, the anode voltage easily exceeds 300Vdc including the screen voltage. If your amp operates in an UL or triode mode, that would not be safe for the tube. As for my amp I use it in pentode mode and regulates the screen voltage to below 300Vdc(BTW my anode voltage is about 325Vdc). It works quite well and sounds good too.
The anode can take more than 300Vdc from most EL84s' manufacturers, the limitation is the screen voltage, most EL84's screen should not exceed 300Vdc with the exception of some Russian tubes such as 6P14 with military specs. To be on the safe side leave the anode at or below 300Vdc, if you operate the amp in UL or triode mode.
In my Chinese version of EL84 amp, it comes with 220Vac transformer when plugs into the 240Vac main, the anode voltage easily exceeds 300Vdc including the screen voltage. If your amp operates in an UL or triode mode, that would not be safe for the tube. As for my amp I use it in pentode mode and regulates the screen voltage to below 300Vdc(BTW my anode voltage is about 325Vdc). It works quite well and sounds good too.
I not sure what you guys are pointing at with this, I did note the cathode voltage, but I don't see how that, or that cathode resistor, changes the fact that the voltage on the anode is higher than the rated maximum, for the anode. Could you explain what you mean a little more?
ttan98, thanks for that, I assume that info just came from experimentation and experience, or is there a way to know this for sure without blowing up a tube? Also, I am curious about this with all tubes, because I have seen several tubes used above their rated maximum, it just so happens that I'm building an amp with EL84s right now so thats what I asked about
Thanks
It's the voltage differences between the tube elements (plate, screen,cathode, heaters, etc) that cause things to start arcing and melting, etc.
So, if in a particular design the cathode is at +100v and the plate is at +400, the P-K voltage difference is 300v-which may be OK. Of course the 100 v cathode may exceed the heater-cathode voltage difference limit.....
The cathode resistor (in a cathode biased tube) sets the grid-cathode voltage difference (bias). This, in turn, controls the current flowing through the tube. By adjusting the value of the cathode resistor, you can control the power dissipated in the tube ('plate dissipation') and keep things from glowing and melting.
All the above is a very simplified version of 'the real stuff'- hopefully I've avoided serious errors!
ELl84 tube data:
TDSL Tube data [EL84]
Tube DataSheets
The Big Tube Data Page
Free Schematics Philips EL84 Tube Data Sheet
Hope that helps!
TDSL Tube data [EL84]
Tube DataSheets
The Big Tube Data Page
Free Schematics Philips EL84 Tube Data Sheet
Hope that helps!
Also worth bearing in mind that if your B+ comes up to full voltage before your heaters do, then no current flows in the cathode resistor and so, with no voltage drop across the resistor, the cathode is effectively grounded...
Fast rising B+ means that at switch on, you can have a significant short term overload of the specified limits, even if the cct works fine within limits under operational conditions.
Fast rising B+ means that at switch on, you can have a significant short term overload of the specified limits, even if the cct works fine within limits under operational conditions.
To be more precise what I am referring is the difference in voltage i.e. voltage between the cathode and and anode, and cathode and screen should not exceed 300Vdc.
I have NOT tested all the EL84 or 6P14 equivalents in the market. The Russian 6P14-EV and Er series should be able to take more than 300V, I would not exceed this more than 10-20Vdc. Other brand of tubes I am not too sure.
I have NOT tested all the EL84 or 6P14 equivalents in the market. The Russian 6P14-EV and Er series should be able to take more than 300V, I would not exceed this more than 10-20Vdc. Other brand of tubes I am not too sure.
A lot of older amps ran EL84 at voltages as high as 400V or even higher, the key is not to allow the screen voltage to substantially exceed 300V, and this depends very heavily on the operating point chosen. The EL84 has been much abused in commercial service.
The 6P14P-EV or ER is extremely rugged and quite close in performance to the 7189, and it even sounds good in most applications. (IMLE, both SE and PP)
The 6P14P-EV or ER is extremely rugged and quite close in performance to the 7189, and it even sounds good in most applications. (IMLE, both SE and PP)
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