FAQs for the N5X
barry (Administrator) 02-24-2015 at 12:59 AM.
Post: #1
The following points address some of the most commonly asked questions on the N5X.
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barry (Administrator) 02-24-2015 at 01:16 AM.
Post: #2
Can I add a switch to switch between the EL84 and octal valve?
Hmmm. Yes, it's possible, but it is not trivial. If it was, I'd have added the feature to the standard amp. It was easy to add the extra socket to allow guitarists to swap out an EL84 for an octal valve, but less easy (and more costly) to make it switchable.

Let's look at the issues:

1) Power transformer - heater current: with both power valves installed at the same time, more current flows in the heater circuit. For some valve pairings (EL84 and 6V6) this may not be a problem, but for others (EL84 and EL34) you will exceed the maximum heater current of the power transformer.

2) Power transformer - high voltage current: The same principle applies. Normally we have current flowing in just one power valve circuit, and we may exceed the power transformer's current spec if we run both at the same time.

3) Output transformer - maximum DC bias: The output transformer also has a maximum current flow as part of its spec. It's designed for 5W output and 50mA. With both valves installed, the parallel impedance is much lower and more current flows. It will depend on the valves fitted, but somewhere in the order of 70-100mA.

So, to properly switch between two power valves in the N5X, you have to cover all three points. Doing this reliably and free of hum/noise is not a trivial exercise:
* switch one leg of the heater, but be aware this wire carries AC current and as you run wires to/from the switch you may inject hum into other wires)
* switch a connection for the plate supply (or the cathode+ground?), which is in my opinion inelegant and likely to create pops and introduce potential failure points in long-term use
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