The only thing I'd add to your advice on re-capping is to check for DC leakage on the coupling caps between the phase inverter and output valves. I know these are nearly always film caps (polypropylene, polyester, etc) and therefore long-lived and not prone to early failure. However, failure of these caps can cause loss of bias and very expensive damage.
Very interesting, thanks Rob. I have a Laney LC30, and have just changed two of the preamp ECC83 valves, because they were microphonic, and a pencil tapped on the control plate (not the valve itself) would come through the speaker. That's much better now. Of the four EL84 power valves, one is microphonic (when tapped), but the amp sounds fine to me. I've been advised to replace all four valves, at great expense. Now, if I just swap out the microphonic one, what's the worst that could happen? Is there a knock-on effect that could damage other components in the amp?
Generally, a tube going microphonic is not a bellwether for a pending catastrophic failure. There are many advocates of replacing all output tubes simultaneously (and using matched pairs or quads), but there's nothing wrong with replacing a single output tube, especially if you're happy with the amp's sound. As I mentioned in the video, you might even prefer a slight mismatch. One caveat: if the amp is being used on tour, then I would recommend swapping out all output tubes at once with a set that has been pre-tested in order to weed out infant mortality. Otherwise, play, enjoy, and save your hard-earned dough.
@@q.b.amplification8056 Thanks very much! As long as it won't harm the amp, then I'll try swapping out the one valve and see if that has any effect, negative or positive.
Thanks very much for your comment. I avoided that can of worms because it's hard to stem the tide of widespread beliefs that are demonstrably untrue. The only meaningful way to compare signal caps is to A/B them in real time - blind. That means not knowing which cap is selected when evaluating its sound. And both caps should have the identical measured capacitance. This kind of comprehensive testing is virtually never performed, but if it was, there would be a lot of embarrassed people who were previously convinced of the nature of perceived differences between capacitors. It's hard for people to accept their own natural tendency to imagine hearing things that aren't there rather than appear ignorant or insensitive. It would be revealing to set up an A/B test with identical caps painted different colors. You can bet your bottom dollar that the orange ones would sound harsh to most listeners who knew they were in circuit compared to the cream-colored ones.
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The only thing I'd add to your advice on re-capping is to check for DC leakage on the coupling caps between the phase inverter and output valves. I know these are nearly always film caps (polypropylene, polyester, etc) and therefore long-lived and not prone to early failure. However, failure of these caps can cause loss of bias and very expensive damage.
Good point!
Oh yeah, and I agree completely about re-tubing. It's nearly always a rip off unless there's something demonstrably, objectively wrong.
Hey Rob.
Very interesting, thanks Rob. I have a Laney LC30, and have just changed two of the preamp ECC83 valves, because they were microphonic, and a pencil tapped on the control plate (not the valve itself) would come through the speaker. That's much better now. Of the four EL84 power valves, one is microphonic (when tapped), but the amp sounds fine to me. I've been advised to replace all four valves, at great expense. Now, if I just swap out the microphonic one, what's the worst that could happen? Is there a knock-on effect that could damage other components in the amp?
Generally, a tube going microphonic is not a bellwether for a pending catastrophic failure. There are many advocates of replacing all output tubes simultaneously (and using matched pairs or quads), but there's nothing wrong with replacing a single output tube, especially if you're happy with the amp's sound. As I mentioned in the video, you might even prefer a slight mismatch. One caveat: if the amp is being used on tour, then I would recommend swapping out all output tubes at once with a set that has been pre-tested in order to weed out infant mortality. Otherwise, play, enjoy, and save your hard-earned dough.
@@q.b.amplification8056 Thanks very much! As long as it won't harm the amp, then I'll try swapping out the one valve and see if that has any effect, negative or positive.
You never touched on the bad and good of signal caps, maybe in a furure post, thanks.
Thanks very much for your comment. I avoided that can of worms because it's hard to stem the tide of widespread beliefs that are demonstrably untrue. The only meaningful way to compare signal caps is to A/B them in real time - blind. That means not knowing which cap is selected when evaluating its sound. And both caps should have the identical measured capacitance. This kind of comprehensive testing is virtually never performed, but if it was, there would be a lot of embarrassed people who were previously convinced of the nature of perceived differences between capacitors. It's hard for people to accept their own natural tendency to imagine hearing things that aren't there rather than appear ignorant or insensitive. It would be revealing to set up an A/B test with identical caps painted different colors. You can bet your bottom dollar that the orange ones would sound harsh to most listeners who knew they were in circuit compared to the cream-colored ones.
@@auburnamplifiers1786 Guitar players are notorious for listening with our eyes.
@@auburnamplifiers1786Shhhh I sell vintage Bumblebee and Black Beauty caps for $40 each. They can sniff the cork while I drink the wine lol.