In my last post I threw in a comment at the end pointing out that lowering plate load resistance will play a part in how the cathode bypass capacitor behaves. Someone asked, so I thought an example of how this affects things might be in order.
Continue readingThere seems to be a little confusion concerning the true effects of cathode bypass on low frequency amplifier performance. The truth is, gain benefits from cathode bypass are limited. And not by capacitor size, but by the basic design of the amplifier stage.
Continue readingRemember when I said that you can’t always get what you want? Well, it turns out you can. At least in this case. Especially if you are willing to shift some priorities.
Continue readingRemember back in the beginning of January when I traced the failure of the Lacewood amplifier to a failed JJ power tube? Well, here we go again.
Continue readingLately I’ve been looking at a revised amplifier design based on the Marblewood project. The intent of the redesign effort is threefold. First, a different and more widely available rectifier tube. Second, an improved, if slightly more complicated, power supply design. And third, some potential improvement in the low frequency response. As it turns out, you can’t always get what you want. But also, two out of three ain’t bad.
Continue readingThere are lots of practices in the DIY world that are more than a little out dated. I’m obviously not talking about using vacuum tubes but rather the methods used in building and testing the circuits we build with them. Many of these test methods came about for very good reasons; perfectly applicable at the time. But as technology has advanced the reasons for many of these practices are no longer valid. And there is really no better example of this than the practice of testing audio amplifiers with square wave (or various sawtooth or triangle wave) signals.
Continue readingAfter a busy Christmas season, including a brief trip out of state between Christmas and new year, I have finally managed to get the Lacewood amplifier back up and running. As part of this effort I also identified the root cause of the initial failure. And frankly I’m a little angry about it.
Continue readingRemember a few weeks ago in the post When it Rains, It Pours! I said that the Lacewood V2 reservoir capacitor had likely failed? Well, I was wrong.
Continue readingHave you ever made a mistake? Not a typical everyday little mistake like forgetting to run an errand, but a blunder of such proportions that you’re shocked by your foolishness? One that leaves you thinking you couldn’t have been that naive, that foolish? Well I did. And it left me with significant embarrassment, as well as some smoke coming out of an amplifier.
Continue readingWould you believe it? Today while listening to the 6V6 Lacewood V2 I heard a funny little popping sound and a short duration whine. It only lasted a few seconds, then it was gone. But when I walked over to the amp there was a distinct smell of “magic smoke“. Once again, the game’s afoot!
Continue readingI have witnessed a lot of electrolytic capacitor failures. Most of these failures have occurred from improper wiring polarity or a significant over voltage condition. They generally involve an explosive emptying of the capacitor shell. These failures usually leave a smoking husk of a component and a spray of foil bits, dielectric insulation, and liquid electrolyte spewed across the circuit, chassis, and sometimes, the test technician. But recently I came across a much different failure. One which seemed to be specially concocted to sneak by without notice.
Continue readingWhen testing an amplifier, the first thing I generally do is to check voltages. This is what I advise others to do as well. However, the real trick is in determining if the measured voltages are acceptable or not. And herein lies the difficulty.
Continue readingThis topic comes up a lot! Someone will email me with, “I want to build {insert project here} from your web site. But…”. Sometimes it’s just that part availability varies. Sometimes people want to use parts on hand which are slightly different. Sometimes people want to substitute tubes, transformers, or whole assemblies. And sometimes people want to actually change the topology! So at what point is the amp being built no longer the design on my website?
Continue readingPlease read the post “That Didn’t Go Well!” before following the power supply change detailed in the later half of this post.
Sometimes a design which seems fine at first can later exhibit some marginal behavior. This exact issue recently reared its head with the design of the 6L6 “Spalted Alder” amplifier.
Continue readingI know it’s been a while since my last post. Things have been a little hectic for my family this summer. Hopefully I’ll be able to get back to more regular posting in a few of weeks.
But that’s not what I want to talk about. I want to talk about the major changes currently taking place in the US economy and our supply chains, and some things we as hobbyists can do to help protect ourselves from problems.
Continue reading