in part two of our fea­ture on valves, Jamie Dick­son looks at main­te­nance and buy­ing old valves, with adrian em­s­ley

Guitarist - - Opinion - Jamie dick­son

Last month, we joined amp-de­sign wizard Adrian Em­s­ley of Orange to find out more about how the ma­jor types of power valve in­flu­ence the tone and per­for­mance of your amp.Tak­ing up the theme again, Adrian ex­plains that as valves near the end of their use­ful life they can let your amp down tonally – and, ul­ti­mately, it will fail al­to­gether. Sim­ple knocks and bumps are likely to take their toll first, he ex­plains: “The main thing you’ll see is me­chan­i­cal loos­en­ing up of the in­sides of the valve. This will man­i­fest it­self as rat­tles and mi­crophony and things that sound like they’re be­ing shaken. Or pops and crack­les, if you’ve got a loose con­nec­tion within the tube.And in a combo, that’s prob­a­bly the first thing that’s gonna hap­pen, be­fore the valve ac­tu­ally wears out.”

If no me­chan­i­cal is­sues af­fect the valve first, the process of grad­ual wear­ing out will make it­self known more sub­tly.“There’s a ma­te­rial on the sur­face of the cath­ode that gets de­pleted be­cause it ends up on the plate over time, due to the op­er­a­tion of the valve,” he ex­plains.“As it wears out, it’s go­ing to go down in power slightly. It’ll lose a bit of out­put and it’s prob­a­bly go­ing to sound a lit­tle life­less, a lit­tle muf­fled. It won’t quite have the chime or the sparkle that it had.”

The last cat­e­gory of is­sues with valves is more spec­tac­u­lar – and po­ten­tially da­m­ag­ing to your amp.“The other thing that can hap­pen is the valve can fail,”he says.“There are a few ways that can hap­pen. One of the com­mon ones is that it loses its grid bias and then it starts draw­ing as much cur­rent as it can and the plates glow cherry red. That will pull from the power sup­ply and you’ll get a 100-cy­cle hum, plus one of the valves will look like a lit­tle nu­clear bomb’s go­ing off in it. So, that’s a com­mon one.The other one is that it can short and blow the fuse, which is nor­mally bet­ter in some ways, be­cause it hap­pens quickly and is less likely to dam­age some­thing else in the cir­cuit.”

Adrian adds that power valves are far more prone to wear than the small, three-el­e­ment or ‘tri­ode’ valves typ­i­cally found in the amp’s preamp sec­tion, con­trol­ling preamp gain, EQ and so on.“As long as they don’t go mi­cro­phonic, preamp valves can last 20 years,”he says.“[This is] be­cause they’re not mak­ing any­where near as much power as the

· “A valve can lose its grid bias and fail… if that hap­pens one of the valves will look like a lit­tle nu­clear bomb’s go­ing off in it” ·

out­put tubes are.The out­put tubes are the real work­ers of an amp, so they’re go­ing to wear down quicker.”

Given all of the above, there’s a thriv­ing mar­ket for re­place­ment valves. There’s also the in­creas­ingly pop­u­lar op­tion of buy­ing so-called New Old Stock or‘NOS’valves. The mys­tique sur­round­ing old Mullards and RCA valves from the 50s and 60s, among oth­ers, has cer­tainly pushed up prices. But are they re­ally bet­ter than what is made to­day?

The an­swer is a qual­i­fied yes, says Adrian, pro­vided they are still in good work­ing con­di­tion.“They are bet­ter tubes than what’s made now, for sure. Like Mullard, Gen­eral Elec­tric preamp tubes, for ex­am­ple, they’re go­ing to be, for the most part, bet­ter sound­ing. They’ll prob­a­bly al­ways yield a bit more gain and sound bet­ter. Some­thing of note with New Old Stock tubes, es­pe­cially preamp tubes, though, is that you should clean the sil­ver-ox­i­di­s­a­tion off the pins. Be­cause there was more sil­ver in the pins back then, that’s why the pins turned black on old Mullard preamp tubes.And they’ll be in­ter­mit­tent in the socket as a re­sult, un­less you clean them with sil­ver dip or some­thing and get that ox­ide off.”

Are there any things you can de­tect vis­ually that might warn you off buy­ing a de­fec­tive old valve, we ask?“Yeah.Where the win­dows are on the plates [the large ver­ti­cal com­po­nent in­side the valve bot­tle, usu­ally dull gray with small ‘win­dow’ aper­tures in­set], if you see char­ring of the glass on the in­side where the win­dows are it means that has been heav­ily used. So I’d tend to avoid that. If you have any kind of valve-test­ing de­vice, then take it with you to see what the valve is yield­ing and test it for real.And, fi­nally,”Adrian ad­vises, “tap the valve next to your ear to make sure noth­ing’s re­ally rat­tly.”

So that’s the lowdown on old valves, but what about new re­place­ments? By pop­u­lar de­mand, we’re go­ing to ex­tend what was go­ing to be a two-part fea­ture into a third part on buy­ing new valves the savvy way, so stay tuned for even more of Adrian’s ad­vice next month.

Power valves are the work­horses of the am­pli­fier and thus more likely to fail than preamp valves

Adrian Em­s­ley says that New Old Stock valves of­ten sound bet­ter than mod­ern ones

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