Erik Mandaville

Wow! It's getting to the point where one can simply hop onto this forum for a peep-show of the hottest-looking DIY audio gear. Looks are but of secondary importance, however. I'd much rather see something like "Hey you all, have a look at this neat schematic of a shunt-regulated, push-pull preamp." Or for those not so shematic-familiar, perhaps a URL link to a website more appropriately set up for promotional purposes. Jeez, even this is too long of a post! It's the weekend, and there's lots of music waiting to be heard! Erik ...and to think of the nonsense someone as helpful as Al Klappenberg has had to put up with?!

You're making a good choices for your short list of speaker contenders! I have both Lowther Medallion horn speakers, and La Scalas. They both have merits, and are both quite different from one another. One common trait is very high sensitivity, which makes them perfect for few watts of high quality amplification. I just finished a complete restoration of a pair of Radio Craftsman 6V6 amplifiers, which sound stunning with the La Scalas. I just want to mention that your interest in a subwoofer may be lessened somewhat if you really give a good listen to the La Scalas. Paired with the right amps, you would be surprised, I think (I was) by the low frequency extension of the La Scalas. That said, I don't think the midrange quality of the LSs is the same as that of the Lowther. I have been experimenting with the combination of the Lowthers and La Scalas together, playing simultaneously. The Radio Craftsman amps have separate volume and tone controls (I like them, regardless of what others say they may do to the performance of the amps!), and have been able to achieve a fairly seemless combination of Lowthers and La Scalas. Carefully balanced in terms of gain and tone, the two systems create an absolutely huge and very convincing illusion of 3-dimensional sound and space. The Horne Shop speakers could be combined, perhaps in the same way, although I don't know their specs. Lowthers and La Scalas are very similar in terms of sensitivity and efficiency. Good luck and have fun! Erik

Yeah! They are working really well. I put on some rather heavily bass-laden material (music, in other words!) last night, and they (grippers) proved very effective. The bass was very much there, minus all the over hang. We've got a nearly 100 lb. yellow lab who sometimes sleeps in the listening room, and this dog snores like an elephant! Shakes the whole floor! I've been meaning to get this done, but have been involved with the repair and purchase of edster's AES preamp, as well as the complete overhaul and restoration of a vintage pair of Radio Craftsman 6V6 push-pull amps -- with ten watts to power the La Scalas woofer in a bi-amped system. Thanks again for your help with this! Erik

Finally I've had (made!) the time to get around to installing the neoprene discs on the bottom of my '89 La Scalas. Per HDBR's prescription, a total of 5 were used: one in each corner, with another in the middle. I had been looking for a good, unobtrusive way of reducing some excessive bass overhang and boom we were getting with the La Scalas in our upstairs listening room -- a suspended wooden floor covered with thin pad and carpet. The way I was reminded of this (elegantly simple and very effective) tweak is interesting: I got my wife a really nice, hand-made music box for Christmas this year. With the lid open and music playing (Pachabel's famous Canon), I set the box down on to a wooden nightstand. I was suddenly amazed by the exponential increase in low-frequency response that resulted from this. It was an obvious and important design element -- almost as if a low, line level signal was suddenly plugged into an amplifier. Ha! The La Scalas are so heavy that the stock metal 'sliders' in each bottom corner were pushing firmly down onto the suspended wooden floor; and this coupled the speaker to a large, vibrating surface -- thus creating the boominess in the bass response. Thanks to HDBRbuilder for such a great remedy! The La Scalas are sounding very good with Moondogs (by the way, Kelly....I bit the bullet and 'upped' the 2A3 plate voltage to 275VDC taken between plate and cathode Wow! a brave new increase of 25 volts!). If any of you are experiencing bloated bass response, and have your speakers located in a similar setting, DO try the Walmart 'Rug Grippers' They WILL WORK! Thanks again, Erik

Do check out the Uttrapath line stage at Welborne Labs. The schematic for the original one is also available from back issues of Vacuum Tube Valley. I have the schemtic for the (non-battery) version, and, just like the Direct Reactance amplifier (also now sold by Ron W.) is extremely simple. Some friends I know who have built the linestage from scratch have commented on some hum-related issues, which Jack E. and others at Vacuum Tube Valley mention as well. In the end, this translates into rather battle-ship like filter capacitance in order to bring it down to acceptable levels. Certainly Ron and Jack, in terms of what is now being offered by Welborne Labs, have de-bugged potential problem areas for prospective kit builders. Another source for a great preamp in a similar price-range would be the Grounded Grid offered by Transcendent-Sound (aka Bruce Rozenblit). He is a very talented designer, with a real wealth of knowledge in audio electronics -- really electronics in general. This preamp is available in both kit and already-built form. Grounded grid circuits are often used in RF applications, and are evidently extremely fast and open-sounding. I'd check that out for sure! It uses 12AU7s (3, I think). I scratch built Rozenblit's first puplished line stage preamp, which was in an issue of Glass Audio. That was also a great preamp, with selectable output impedance (high and low) for good amp interface. You might also have a look at the Bottlehead Foreplay. This can be purchased as a kit for a little over $100. Although it uses an AC filament supply (which can cause hum), it is still a very good, direct-coupled-low impedance cathode-follower circuit. For the money it's hard to beat. I built both the original kit (a few years ago), as well as more recently, my own tube-rectified version, which also uses a dedicated DC filament supply. It is really easy to build! Folks at Bottlehead have also just released what I've read to be a very good phono stage -- if you're interested vinyl. In addition, you might also check out ebay for Dynaco stuff, such as the very well-known and respected PAS-3 preamp. My brother uses this, and absolutely loves it! I also have a PAS-4 (solid state)that is very, very good sounding. Fortunately, I haven't gotten so locked into tubes that I can't find good possiblities beyond the hollow-state landscape. I got this preamp for $37 on ebay, and it looks and performs as new; and coupled with tube amps sounds much better than it should for such a modest price. Good luck in your search! Hey, if you haven't done so already, you might also consider, at least temporarily, a passive linestage (really just a volume control in a box). If you have your source equipment within very short distance of your amplifiers and speakers, you might try one of these. There are no active components of any kind, just simply a volume control and switching capability. One issue with this is the problem of comparatively higher output impedence (say, around 10K ohms...)trying to drive an interconnect -- which if too long causes roll-off of high frequencies. These a an absolute snap to make, using cheap but effective parts from Radio Shack. In my own experience, though, they just don't have the drive and impact of a good active gain stage. Have fun a good luck with your search! Erik Also check out the Bottlehead Foreplay

Kelly: Hope you are having a good holiday! I wish I was in the position to send you a picture of the new-improved (well, I think it is, anyway...)version of the AE-1. At least it no longer has the gaping hole in the front panel. It's back to a completely functional, dual mono (including power supply)configuration, and 95% of it has been rewired. I encountered one problem after the other with it. Both PS and preamp sections were grounded at different points all over the chassis, which doesn't help in terms of influx of spurious noise and ground loops. Both preamp and PS now have a separate, single earth ground which for some reason always works better for me than a single ground common to both sections. Finally, a small-value grid stopper resistor was used on each volume control to get rid of some RF noise I was getting from some nearby transmission antennas. I also always use high voltage ceramic caps on either side of the AC line input to ground to snub line transient, as well as similar .01mfd ceramic capacitors across the power switch -- a trick I learned from a Dynaco PAS-2 schematic. Totally cures the little pop one can get if one forgets to turn equipment off in proper sequence (which I do all the time). It't like new; I love it!; and I totally support your suggestion of a 6SN7 based preamp to the original author of this thread. Erik

Hey, great job on your purchase! Al's networks are built to very high standards, and many are very, very happy with their performance. I am probably going to build myself a pair from the schematic Al has (unusually and most generously)made available for other DIYers. I'm going to have to do this 'on-the-cheap' for the time being, and use a variable L-pad on the midrange horn, rather than the the autoformer used in both Al's network and the stock Klipsch crossover. Doubtless a few might jump on my case about this, but one can actually build a very good crossoever with such a built-in voltage divider as this -- I speak from having made several networks that use variable rather than fixed L-pads on both the tweeter and midrange branches. Once set, the variable L-pad can be replaced with fixed resistors. But to your tweak question! You might indeed experiment with bi-wiring (or perhaps later, even bi-amping), since Al has insightfully made provision for this modification. I know several exceedingly knowledgeable listeners who really prefer to bi-wire their speakers. Since speakers present a fairly reactive load to the amplifiers, they are usually more sensitive to the kind of wire used to make the amp-speaker interface; thus differences between wire used for speakers can often be sometimes easier to discern than than that for upstream components. Replacing the short lengths between the driver terminals and the crossover might have a small effect, however you may notice a greater difference when working with the longer lengths between your amplifiers and speakers. I have built many, many different cables based on a variety of geometries, including a simple cross-connect between a twisted pair of low-capacitance (measured to be approx 14pfd./foot) coax. Even Romex cable sounded really quite good (I could care less what others might say...). Of late -- and this is something you might care to try -- is a braided cable of 4 twisted pair of CAT 5 cable. This is available at Radio Shack for about $.30/foot. It is insulated with blue PVC rather than the more common gray. The blue insulation is important in that it contains twisted pair conductors insulated with thin Teflon, rather than PVC. There are those who have braided gigantic versions of this, consisting of many, many twisted pair -- ultimately creating a cable with seriously high capacitance issue...so much though that they caused oscillation in some amplfiers. You can also find spade terminals at Radio Shack that will fit the terminal strips on your new crossoevers -- this connection is important and shouldn't be an after thought. Do try bi-wiring, though! It's easy to do, and you may really like what you find. It enables the use of wire more appropriate for the frequency ranges of the drivers they're being used for. I'm in the process of doing some dismantling of the stock x-overs on my La-Scalas for the same purpose, however my plan is to go a step further and eventually use different amps for the tweeter and midrange and the woofer. Al clearly marks the inputs and driver outputs on the crossovers, and they should be a snap to install. Ed's idea of a vibration absorbing buffer between the crossover and speaker cabinet is a great idea. Some manufacturers even encase the entire crossover in epoxy or silicone for the same reason. I've also done that on some of the loudspeaker systems I've built. Anyway, have lots of fun and enjoy your new networks. They look very nice, and I wish I could afford them, too! I've got to get a now truly fine sounding AE-1 preamp paid off first, though! Keep us up to date, and please let us know how you like the performance -- I'm really interested! Friendly Regards, Erik

Right. Point is, though, that very little credit had ever publicly been given to the originator of the idea. Tweaking a circuit is quite a bit easier than concieving it, I would say -- I've tweaked lots of circuits, including the Fourplay. I built my own Foreplay from scratch, but used tube rectification and a dedicated DC heater supply. The most frequent complaint about it from new builders are buzz and hum problems, often fixed by either filament snubbers (bandaids, but they work), or a filtered DC filament supply. Anyway...I like giving credit where it's due.

Kelly: Honestly, I'm really not letting any previous sour grapes get in the way of enjoying my Moondogs. I like them very much, and they are still the best amps I've owned. I tell you though, that little ASUSA shocked the hell out of me (not with electricity!) by how good it sounded with the La Scalas. I've done work on the Moondogs to get them to where they sound and function best for my needs -- and I haven't done anything to them in a long while except listen -- and even then not to the AMPS, but to music. For me that's the best compliement I can attribute to an audio component. Know what? I still have some of the parts I bought for the Direct Reactance Drive amp. I guess you know it's not an original Welborne circuit, but one by Jack Eliano of Electra-Print. I just ran out of funds...good transformers are very expensive, especially since I was going to build mono-blocks. The fact that it's SS rectified (very smart circuit in that sense, too, since it uses appropriate resistors and capacitors to protect diodes wired in series). I spoke with Jack E. on the phone about this -- about art, as well...he is a very helpful guy, and said to stay in touch when I started building them...if I needed any help, feedback, etc. Of the Wright 2A3s, I have a very good friend who is in turn quite good friends with George Wright. This friend of mine alos owns Moondogs, a couple of 45 amps, and others. He is nearly 80 years old, and has very, very extensive experience in this. He said he like the new Wright, tube rectified 2A3s (post 2000 model, I think) much better than the earlier rendition. I was just trying to give the original author of the post an alternative to the Moondogs, and hadn't thought of the Direct Reactance amps. By the way, I once mentioned on the Bottlehead site that the Foreplay is really a George Wright design, given to Doc B. and company to use. So many owners had been crediting him for such a fantastic preamp, that I just couldn't keep my big mouth shut. Jack Eliano also has what I've heard to be an amazingly articulate and fast line stage, which I also have the schematic for. I'm so happy with how the AE-1 sounds now (finally!), that I don't have more plans for a preamp now, other than to maybe build a good phono stage for it. Sheesh! this is too long...time for some rest! Take it easy, spend lots of time listening to music, Kelly. Erik

Those are nice shots, Kelly. That 'nifty' circuit is the absolute heart, spine, brain, and any other critical human counterpart one might include among those. I have found myself that less expensive capacitors (wright's look very much like the ones I use...)can sound very, very good. And if some like something else, than they should use them. I prefer my tea with very little sugar, others like more. I also like the form/function relationship of the Wright 2A3s. They are a simple strong box that contains an evidently very effective circuit topology. To me that matters more than anything else. Man, these posts take lots of time. I envy those who have the energy to put so much into them. I'm tired from teaching all day, and would rather go and listen to some music. Take care, Erik

Have a look at George Wright's equipment. He's got amps that are easily on par with Welborne's. Great designer, incredibly durable build quality, very good reviews from competent and knowledgeable people. You'd have a number of choices as well: 2A3, 300B, 45 monoblock amplifiers and a few others. I have a couple of friends (with many, many years of SET experience -- like 50 years!) who say the new Wright 2A3 amps are quite a bit better than the Moondogs (which they happen to own, as well...) If you wanna build your own, there are still a few options for that. Bottlehead, DIY, and a few others. Good luck, Erik

Correction!!! The amp should NOT NOT NOT buzz like that. I had a typo in the opening sentence concerning this. I found the schematic online, and see the rectifier are EZ-81s (2) wired in parallel. Tom the color coding I gave you for the wiring is correct. Check those very carefully for damage and possible shorts. I don't have those rectifiers, unfortunately. But I would urge you to try to get a couple of extras if you don't have them already. By the way---I'm assuming this piece you're working on IS in fact an Eico HF-81, correct? Good luck, Erik

Tom: That amplifier should buzz and vibrate like that. The symptoms you're describing most likely have nothing to do with how tight the transformer is bolted down. Some of the things that can cause buzz and vibration like this are: 1. Shorting secondary transformer windings (are there any leads that aren't being used that might be making contact somehow). Also make sure the hole in the chassis where the trans. wires come through is chaffing the insulation, exponsing the conductors. Check the high voltage secondary (usually red), the filament windings (usually twisted green pair) and if a tube rectifer is used, the usually yellow leads. 2. Malfuncting diodes and rectifiers can cause this as well. Is the unit in question tube rectifier? Try changing it for another. There is sometimes a condition referred to as 'motor boating' Did you ever rewire the power transformer primaries to where they connect to the switch and fuse. Try putting in a new fuse. If you have tube replacements, check with new ones to make sure you're not getting an internal short in one of them -- really try a new rectifier. What's that thing use anyway? Maybe I have one I can send you. I've got 6X4s, 5Y3s, and a couple of others. If it's solid state, go to Radio Shack and get some silicon diodes with a good high voltage and amp rating. Does this use a full-wave bridge rectifer (string of 4 diodes, one end grounded) or just a simple full-wave, which uses a grounded center-tapped (look for a red transformer wire with yellow stripes going to ground). Make sure that connection is good and strong. This vibration and buzz should not be there, and I would really cuation use of the amp until you find the problem -- could cause over-heating and serious damage to expensive parts. It sounds like it would be easy to fix, though! Erik

I feel sort of compelled to offer a little bit of defense for Mobile's (and his colleague!) interest in rejuvinating, updating, (subjectively) improving, etc. a successful tube design from the past. My opinion is that science and art are strongly derivative, in that modern or contemporary approaches to design and design implementation rely very strongly on previously established groundwork, ideas, concepts; and in this case, an already highly regarded musics playback system (the HF-81). The Wright Brother's little plane also flew, so why go any further? Certainly this is a simplified analogy, however there are some similarities, I think. Regardless of what others might perceive as a waste of time and energy trying to improve somethng that already works just fine, I can't help but respect the dreaming, thinking, planning, and so forth that goes into the creative act -- whether a sculpture or painting or music making machinery. It's what helps people grow as individuals and, even in failure, teaches lessons and provides knowledge that greatly surpasses sitting, doing nothing, and accepting things as they are. I don't even know how many times I've heard people say something like, "My grandpa always used to say, if it 'ain't broke why fix it?!" Sure, that has some sense behind it, but it's also an easy way out. My belief is that things don't necessarily have to be broken in order to be improved upon. In working with and listening to vacuum tube (hollow state) audio equipment, we are essentially resurrecting an antiquated and obsolete technology. But many are doing this because of having the very unique opportunity of being in the position to compare and contrast currently available music playback systems with those of half a century or more ago. So newer in fact, in some cases might not be better. Nevertheless, an ACTIVE interest (one that is willing to question, experiment, and work-through by trial and error), is what can absolutely lead to really neat discoveries! Moreover, Kelly cares enough about this interesting concept to build it around a very special chassis design. I think the circuit planning and design should really be the first problem to solve, but the fact that its 'house' is already being given attention illustrates a healthy confidence in and a respect for a great tube amp. from the past. Things like this need to be encouraged! Erik

Hey! I just grabbed a handful of rice crispies, and then thought of this! I haven't actually measured the available space on top of the AE-1 chassis, but there may in fact be room for dual, 5Y3 rectifiers. The AE-1 already uses two separate full-wave rectifiers coming off the single high voltage secondary, and as such also uses two separate capacitor input filter sections. All that might be needed is a power resistor adjustment in order to obtain correct voltages for the preamp. I might bread=board this off the chassis, and just run wires to the load. This might be interesting! hmmmmmmmmmmmmmmmmmmmmm Erik It's not even mine yet, though! Guess I'll have to wait before I pull out my chassis punches.

Hi Kelly: First off, your Eico project sounds really interesting, as does the wood you have found to use for the chassis. Things like that can make for a very personalized touch, and turn out to look awesome. I agree with you on the simplification of the circuit, as well. But each to his own in terms of needs, desires, etc. I hope you'll keep us posted as this project begins to unfold. Yes, that's the preamp I've been working on, though the front panel no longer has a hole in it. I much prefer a dual-mono volume control set up, and put in two 100k pots I had on hand. High quality resistive elements are good for stereo controls, where more accurate tracking is needed. With two mono controls, one can even help offset differences in tube gain, making close matching between tubes less imporant. The coupling capacitors (large ones, too!) were flopping around loose inside, since the tie point they were attached became unglued -- sort of like the terminal strips on my Moondogs. The wire nut seen in the picture on the yellow 5 volt filament leads (for a tube rectifier not used on this) is just a plain bad idea. If the wire nut happens to cut into the insulation, the leads can short out. Better to cut them to slightly different lengths, bend over the tops, and then simply tape them off with electrical tape (which is what was done). There were also many leads that were far longer than they should be. All that said, I very much respect the first builder for making a great effort. I still have the first amp I put together, and have not changed the wiring becuase it makes me laugh to look at it. What a rat's nest! Ed has not sold it yet, but the author of the post is interested! Just don't know if I'll be able to afford it! You all have a good day today. Hey, Kelly? do you happen to know how your SET friends are taking the B+ reading on the plates of their 2A3s? Plate to ground will give a reading that is about 50 volts higher than what it actually is. Erik

Hi Kelly and Deang: Kelly, I must admit to wanting to learn as much as I could about tube audio design, which began with tubes other than the 6SN7. The 12AU7 variants are also very good tubes, as is a surprising sub-mini triode, the 6021. The latter tube is not much more than an inch long, and has been the tube (just a single one) in the preamp I built after an Eric Barbour schematic. That same preamp was used by the staff at Vacuum Tube Valley for some time. Eric Barbour also contributed a recent article, with information on a 6SN7 based preamp, which uses a 5Y3 rectifier. This one is on hold right now for a future project. If you like that tube, you should try building the design. You've never mentioned your experience in building, although you have talked about swapping coupling caps. I think you might enjoy the process of building something of your own. Anyway, I've got that AE-1 preamp up and running very well, and rewired the volume controls in the conventional fashion. So I guess it's 'bout time' as you say, however, that is really sort of a relative issue, and I've been busy doing restorations of 1920s radios and other similar things. I'm actually fairly familiar with AE-3, and considered that as an option for quite some time. As I said, though, I prefer the challenge of building completely from scratch, and in so doing, learning more about the process of circuit design and implementation. 'Liquid' is a subjective term, which I qualified as (my opinion) ...and Kelly: Great about the 2A3 voltages, by the way...higher voltage can sometimes improve linearity as well. Current production 2A3s can certainly handle voltages in the 300 range or even higher -- I've known that since the time I decided to lower the plate voltages on my NOS 2A3s. So go for it and crank it up! I'm leaving mine exactly where it is. I would suggest the same for anyone using old 2A3s, and be wise enough to follow RCA specs for 250 volts. My tubes were not cheap, and I would like them to last as long as possible -- I'll swap (subjectively) less dynamics for that any day. Thanks for your replies and thoughs, Erik

A friend recently sent me his ailing AES AE-1 preamplifier (Audio Electronics Supply - DIY division of CARY Audio)to check out and possibly repair. One channel was evidently not working properly. This piece having been built by another individual, I believe it came to me second or third hand; and as such, I was just a little reluctant to use it to feed a signal to my amplifiers. Normally diagnosing an electrical problem would involve listening to the offending component, but I took off the bottom plate and to check out the circuit and wiring without ever having played it. I also didn't have a schematic, which would have been helpful. I believe AES does in fact sell these -- someone on another forum mentioned he thought they cost around $25. Anyway, there were things I could check out without the circuit diagram. The builder replaced the dual mono volume pots with a good quality stereo NOBLE, and this subsequently left an unsightly hole in the front panel. I initially thought the volume pot wiring was done incorrectly, but closer examination revealed simply the use of a 'shunt type' attenuator circuit. So that was alright. I have always preferred two mono attenuators to a single stereo control, and returned the preamp to its original dual-mono arrangement. High voltage rectifiers (dual full-wave fed by a single power transformers)had a damaged diode in each channel. Those were replaced. Regulated DC current is used for the 12 volt filament supply (6SN7 heaters wired in series), the diode ring that forms the full-wave bridge looked very sketchy, and was in serious danger of shorting against the chassis. I installed a new rectifier and filter section. Several joints were also found to be either cold or altogether unsoldered. Not having any specs to go on, I checked to make sure all high voltage filter capacitors were working, and B+ voltages were within range for the 6SN7, of which this preamp uses a total of four. 6.3 volts is what would normally be imposed on the filaments, but the 12 volt regulators reduced this only minimally -- if nothing else, the tubes will just last for a long while. I share all of this, because I simply did not approach this repair with the expectation of enjoying the sound of this preamp as much as I did. I have built several designs from scratch over the years, but none based on this outstanding tube (which are also used in the input/driver sections of the Moondogs. I knew that AES offered very high quality kits at comparatively reasonable prices, but was just always interested in building my own. Having put the piece back together and installing 4 JAN tubes (all registerd very strong on my tester) I put it into the system night before last. It took a very short while to discover that this circuit was very, very good, and easily preferred to the other preamps I've constructed. Music, although not euphonic in the least, had 'cleanliness' and liveness to it that wasn't there before. Small details that previously had trouble making themselves heard, suddenly spoke out with outstanding clarity. I don't care for 'liquid warmth' which to me is another way of saying 'dull' (that's just my opinion....), and this preamplifier exhibited nothing of that. It was just really great sounding! The only other thing I might do, and this with the permission of the owner, is increase volume sensitivity a bit by installing a 250K control instead of the 100k now being used (simple, $1.50 carbon pot that sounds just as good as those I've purchased for $35-$50). 250K is more sensitive in that less signal is sent to ground, meaning that the controls don't have to be turned up as high. This is the first time I've heard a 'CARY product,' and I was enormously impressed by the quality of parts used and overall build of the component. Very good quality center-tapped and potted transformers are also used, which one doesn't find too often in a kit product. I'm also used to the sort of battleship like aesthetics of my own home-built pieces. I have always preferred the form/function relationship, but the AES products have a little of both. They look really nice in an understated fashion. What a great addition to the system -- the thought of probably having to return it to its owner is one I regret! Happy Thanksgiving! Erik

For those of you who have Moondogs, have another look at the great picture jazman shared of the wiring in the Moondogs -- a wiring tour de' force at that! Most of us are using the Moondogs either factory wired, or built according to the directions that came with the kit. If you are familiar with the wiring layout, the filter capacitors used to smooth the DC in the 6SN7 heater supply are two, paralleled 10,000 mfd. caps. These are the bright blue capacitors near the large, dual-section electrolytic attached tot he side of the chassis. This is an interesting modification you all might want to consider. I call it a modification, because the schematic shows just a single 10k, 35 volt (or thereabouts) electrolytic. If you are experiencing any extra hum beyond what 'silence' may be obtained in the null-area provided by the hum balance potentiometer, what you may be hearing -- especially with very efficient speakers like Lowthers or Klipsch -- is a need for slightly great filtering in the 6SN7 rectifier circuit. This would be a rather unobtrusive hum heard only when the amps are idling, with no input signal, and within a close proximity to the speakers. I in fact tried a very similar thing with some $.25 2000 mfd. caps, with some result, all of which was not desireable. There was a definite quieting of the already very low-level but audible hum (not buzz, that's another problem), but at the expense of perhaps some life to the music. But the caps were dirt cheap, and may have been very poor quality, old, or both. The guy who wired jazman's amps knew what he was doing, as can be seen in the very nice wire dress and layout of parts. Adding more capacitance could be a wise move in this situation, and is one I'm going to try again this weekend. I'm going to have a look at a broken preamp for a friend, as well as begin a restoration of an old Sears Silvertone FM radio, and then take some time to work on the Moondogs. I am also going to try to by-pass the 6SN7 Bridge rectifier. No, not to use AC on the filament supply, but employ a hum-cancelling circuit that can be made from two power resistors, instead. I've been looking over the schematics of some other amp designs (all SETs like the Moondogs)that use a similar hum-reducing circuit. Anyway, I thought I would just point this out. If you are getting more hum than you want, or find yourself wondering if that low-level hum should or shouldn't be there, you might try adding another 10K capacitor in parallel with the first to see what happens. BUT!!! Be sure the power supply caps have discharged before you mess around with anything. They can pack one hell of a jolt if still energized. The builder of jaman's amps also included a neat witch to bypass the power resistor across the B+ filter capacitor. Welborne runs the 2A3 plates pretty high already, so much so, that I reduced the B+ by using a different rectifer, and a larger resistor. If you do this, it's good to balance out the voltages in the input and driver stages, as well, since all of those come off the main B+ rail. Oh, one other thing here. I was looking at on an old Dynaco PAS preamp schematic a while back, and noticed the use of a low-value (.01mfd, I think) high voltage capacitor (use a ceramic 1k-volt from Radio Shack)across the power switch. This works great, and I use them on all the preamps I've built, as well. If you get any 'pop'or snap when flipping the switch off, the capacitor will 'snub' that resulting arc, and preventing from traveling down-stream to your speakers. I did the same thing on the Moondogs. A volume control has also been a nice addition! Anyway, I just wanted to share some of this with fellow Welborne Moondog owners. Erik

Max: I'm a teacher, and have worked with students of every age level and experience -- I should add that I teach art. If you knew how many times I have heard 'I can't do it!' from my students, you would understand why I know you would be abel to construct a kit preamplifier. It's easier than setting VTA, JFK, LBJ, or any 3-letter combination we can think of! The main thing is that you want to try -- which maybe you're not into right now. So it doesn't matter! Enjoy what you like doing, and forget about it for now. Take care and regards, Erik

Hi again, Max: I very much agree with what you've heard about the fortes' of SET designs. They really do incredibly well with high and mid-range frequency information, and the midrange composes the greatest bulk of recorded material. I'm jealous of your REL sub! I've heard that they are very, very musical subwoofers, most of which to me sound like one-note thumping. If your main speakers go down to 50 cycles, I must say that in my opinion that is nothing, as is sometimes said, 'to sneeze at.' Actually, I've never found myself sneezing or prone to any other allergic reactions simply by not finding a particular issue of much importance! A good solid 50 Hz can sound impressive! Of course, I don't use my system (or any system, for that matter) for home theater, and actually wish my speakers and amps were not the either side of our TV. It just happens to be a design and space constraint. I never have the TV on when listening to music, or vis-versa, of course. Max: Don't short change yourself! You may be surprised at what you are able to do as far as DIY electronics. It is honestly great fun, and it can teach you a great deal about the way your system behaves. Have you thought of maybe building a simple kit? check out the Bottlehead forum (you can get there via a link on the AA asylum. Sorry, I can't remember the URL offhand. There is an extremely good preamp kit (which I built my own version of -- using a tube rectifier...gee this sounds familiar!)for just over $100. It is a direct-connected (first half of a dual triode to the second half --- without using a coupling capacitor), cathode follower, that has a very low output impedance. It is an outstanding performer for the money, and the instructions are very easy to follow. You could work on it a little be each evening or on the weekend. I would be happy to help with anything you might have problems with -- I know this preamp's schematic virtually by heart. An added bonus, is that the people on the Bottlehead forum (unlike another one I'll keep to myself) are always willing to help. Think about it! It's not only a great education, you will get a very capable, high performing line-stage (no phono section) when you're done. I look forward to hearing what you have to say about your new amplifier -- it must be exciting waiting for it to be completed. By the way, it's possible to also get really nice SET amp kits! Erik

Tom: This is exactly how I have started to get back into my record collection. But I found my old Technics table in the back of one of my parents storage closet while visitng them in Tucson this summer. I bought an inexpensive but amazingly-good-for-the-money Walco cartridge (hell if I know if it's aligned right -- I need to get a good guage!), am using a GREAT 9 volt battery powered (former Radio Shack product)MM phono stage. I've got a few schematic for tubed phono stages, and plan to build one of them this coming summer. This sounds like a great find for you! Have fun, and beware that it's addicting (but what's new about that in audio!?) Have Fun, Erik

It seems to me that the La Scalas could be really good candidates for a bi-amped arrangement: SET 2A3 for the high and mid frequencies, and something a bit heavier (maybe say 10 watts instead of 2 or 3!) for the low end of the spectrum. I'm very curious to learn if any other members have done this recently (or in the past) in their two-channel stereo systems. My home theater consists of a 27" Sony TV, and that's it! My wife and I hardly ever watch TV, so haven't invested in anything very elaborate. But back to the point: I own the AL networks, and would like to separate the woofer branch of the network from the other two. Both (actually 3)amps have volume controls, which could then be used to balance the overall frequency response of the speakers. With such a set-up, it could well prove worth-while to use a small, high quality transistor-based amp for the bass. I would very much appreciate any thoughts or feedback on this. I've never used a bi-amped system before (mainly because I've been using a single range driver for the past five years...), and can see how using a dedicated amplifier for each end of the audio spectrum might be a good idea. Thanks! Erik

Max: I think you are thinking in exactly the right direction! I do nothing but respect your honesty with this, and learning from listening must be the ultimate test concerning what is best for you. All though I have had great enjoyment building and restoring, there are times I really wish I would just leave things alone and listen to music. I've gotten sick to death (almost...) of switching out different kinds of cable, and had gotten to the point actually where I couldn't remember what was what anymore! In short, excellent decision on your amplifier choice. Diodes will likely provide a little tighter control and speed of the lower octaves, and I have heard (or read) some say they think tube rectifiers sound mushy and that they lack the precision of solid state AC to DC circuits. So all this blabbing about tube rectifiers (including my own!) should be put aside for awhile -- which it sounds like you're doing. I would certainly trust some of Odysius's thoughts on this, since it really sounds like he knows what he is doing -- far more than I do, I'm sure! Take Care, Erik

John: I'm curious about what modifications you made to your AA networks. Al has mentioned the disconnection of the two diodes (really just one to break the circuit), and a couple of other things. Did you also do the diode mod, and what was the result? Thanks, Erik