You Ask: What replacement tubes are suitable for longer amp usage?
Not cranking an amp consistently? It may be time for new tubes that’ll go the distance.
In this new Q&A series, we address some of the questions sent in by our readers. To kick things off, we have a query from Eric Nelson, who wants to know what replacement tubes are recommended for the long haul.
Eric asks: “I have A Fender Super Champ X2. Could you please recommend some good choices for replacement tubes for it? Since I live in an apartment, this amp will never be cranked. I think I would rather go with something that will last a good while. Also, I have the Vox ToneLab. Could you please recommend a replacement tube for it?
Are you happy with the sound? If the answer is no, it might be worth having a tech check the bias setting of the power valves before you install new ones.
Fender is known to run the X2 power tubes fairly cold, and setting the bias is an easy procedure because a 1-Ohm cathode resistor is wired into the circuit, along with a bias trim pot. Bias it warmer and you’ll get earlier power amp overdrive and softer dynamics. You may even decide that the factory power valves sound fine after all.
You’ll have to check the bias anyway if you install a new pair of power valves. Simply replacing power valves in an amp that isn’t cathode biased, without checking the bias is not a smart option. If you do decide to go ahead, a pair of JJs will run to £24 and a pair of new old stock Phillips will be £50. You need to request a matched pair and you may have to pay a ‘matching fee’.
On the other hand, preamp valves, such as the 12AX7 in your X2, can be swapped like for like and you can just go with the one that sounds best. Buy from a reputable dealer like Watford Valves and they will test for low microphony. Prices may be cheaper on eBay, but you’ll be taking a risk. If the valve fails or sounds ringy and rattly within a short space of time, a dealer should replace it. Which brand depends on your budget. You could spend £35 or more on a new old stock RCA or Phillips. I’ve had good results with Harma valves, and prices range from £12 to about £18.
As I recall, the Vox ToneLab uses a 12AX7 as a pseudo power valve to drive a ‘virtual transformer’, and is configured in class A or AB, depending on the model selected. In this case, both sides of the dual-triode 12AX7 must be matched, and you should specify this when ordering from a dealer.
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