NOSValves Posted March 6, 2003 Share Posted March 6, 2003 Oh and I can tell you right now that amp could easily be changed to manual bias for about $20 !! Quote Link to comment Share on other sites More sharing options...
Deang Posted March 6, 2003 Share Posted March 6, 2003 I've searched the web endlessly. I called Mike Sanders and though he was very nice about it -- said no way. I am most definitely interested in manual adjustable bias. That would be the bomb. It's the ONLY thing I don't like about them! Kewl. Quote Link to comment Share on other sites More sharing options...
Deang Posted March 6, 2003 Share Posted March 6, 2003 12AX7 & 12BH7. Can you guys tell by looking if that's a silicon diode for the rectification? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 6, 2003 Share Posted March 6, 2003 That is the same driver tubes as the Dales Mark III's !! All triode front end. The adjustable bias would be pretty simple but I still find it hard to believe that you can run KT-88s in that amp seems like the voltages would be to low but I'm just guessing. Why won't the guy give you a schematic that is redicules unless he just doesn't have one. I have no idea how you can be nice and deny a customer information on the amp they own !! Craig Quote Link to comment Share on other sites More sharing options...
Deang Posted March 6, 2003 Share Posted March 6, 2003 I knew it was SS rectified when I bought it, and of course there is no rectifying tube. I wasn't much concerned about this, since my last three amps used it, and I was happy with all of them. I certainly think there is more to how an amp ultimately sounds than whether it is tube rectified or not. Yes, it is a very simple design. A little over a two dozen parts overall, and only 5 parts in the signal path. Kelly voiced some criticism over the parallel arrangement of the EL-34's. Most of what I read seemed to indicate it was more of a good thing. What sayest thou? Quote Link to comment Share on other sites More sharing options...
Deang Posted March 6, 2003 Share Posted March 6, 2003 Well, they use a cathode biasing scheme, and I can run KT-88's, KT-90's, etc. I just have to make sure the tubes are matched using real voltages (under load) -- I think I have that right. The truth is -- they will always sound best with the EL-34's. Based on my understanding of cathode biasing -- it works good if you stay with the same tube type, not so good if you go to something else. Believe me, I have no problem with the EL-34. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 6, 2003 Share Posted March 6, 2003 Dean, what are the values and what pin are the 4 Identical and which look to be Vishay Dale black resistors running to ground off the each output tube. I have a feeling this amp is not cathode biased but fixed biased and could be changed to adjustable. I may be wrong but why would the amp have a bridge rectifier if it was cathode biased Mark ?? Craig Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted March 6, 2003 Share Posted March 6, 2003 Those are nice looking amps, and straightforward layout. Paralleling output tubes has been done for years, and is a simple way of increasing output. One can't simply just add another tube, however. Paralleling will reduce by half the plate resistance/s of the output stage, which requires an appropriately matched OPT. This is actually something I'm very interested in doing to my Moondogs, but would need to get an output transformer with an approximate 1,700 Ohm primary. Such an arrangement can also improve distortion potential, as well. That said, every time I turn my amps on I love them with the very few refined watts they offer. It's plenty loud, and I know my interest in the parallel issue comes from simply wondering 'what if?' If your amplifiers sound good, great -- they sure look nice! Erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted March 6, 2003 Share Posted March 6, 2003 I make out a full-wave bridge rectifier (solid state) connected to the red secondary winding of the PT. There are cathode resistors bypassed by what looks to be an oil capacitor -- this of course can be seen referenced to ground. I can also see a very smart addition, which should have been added to my amp kit! Looks very much to me like an MOV across the PT primaries. Great protection again voltage spikes. First input capacitor looks to be a high voltage 47mfd. electrolyic (consider getting a nice Solen poly cap for that, instead -- this exact value is available, I believe.) But, I might be wrong, but I could swear the filaments are heated with AC -- I'm searching for a hum cancelling circuit?! Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted March 6, 2003 Share Posted March 6, 2003 Nope! Capacitor input is one of the biggies on topside! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 6, 2003 Share Posted March 6, 2003 Mark my eyes must be about as bad as yours ! Now Erik must have the eyes of a eagle because he sure can make out a heck of allot more then I can ! Craig Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted March 6, 2003 Share Posted March 6, 2003 Craig: Check out the twisted red PT winding, see where the are connected to the ac input on that SS rectifier (the two ac connections are bent over toward the rear of the rectifier). But see the green twisted filament winding? They are going straight to the filaments with nothing in between as far as I can tell. I can't find a hum reducing circuit anwhere. I can't remember now (sheesh my memory is getting lousy) if this was a PP or Parallel output. If PP, the AC filament issue is such a big deal, since most of it is reduced by the nature of the circuit. Still, If the PT can handle the extra load, I would consider an additional rectifier and filter section (full-wave-bridge)with something like a 10,000 mfd. electrolytic across it. Neat looking amp, though! Erik Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 6, 2003 Share Posted March 6, 2003 Oh I agree its a neat looking circuit and I bet it can be built pretty inexpensively that is why I love to get my hands on a schematic !! Craig Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted March 6, 2003 Share Posted March 6, 2003 I'm thinking along the same lines, and wonder if that may be the reason why a schematic won't be given away -- which is absurd, I think. What is the problem??? It's only fair to supply a buyer/owner/user with a schematic diagram of the circuit. I have schematics for every radio (even my really old wooden Crosley and Atwater Kent receivers...and the Hammarlund, too!), preamp. or amplifier I own. The Moondogs came with a schematic, and even AES sold a schematic when I needed to finish up repairs and check voltages on my (ulp, swallow....)AE-1 preamp. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 6, 2003 Share Posted March 6, 2003 Yea there has to be a schematic somewhere I can't believe that there was not one provided with the amp when it was originally bought. I would of thrown a sh!t fit if I bought it new and they wouldn't give me a schematic. It would of been returned instantly !! Craig Quote Link to comment Share on other sites More sharing options...
Deang Posted March 6, 2003 Share Posted March 6, 2003 Craig, I love you man -- you're a trip. You're also full of sh!t. You'd have this thing on your test bench with a piece a paper, and have the whole circuit diagrammed out in 45 minutes. A schematic probably wouldn't tell you everything you need to know about the transformers anyway -- they're specciaal. Custom wound to his specs (whatever that means), and the associated info is not likely to be on the schematic. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted March 6, 2003 Share Posted March 6, 2003 Oh but there are ways to figure that stuff out !! There is always my good buddy Mark to help me there. I just think its crazy that he won't give you a schematic ! Did he tell you why ?? Oh and I love you to buddy !! Craig Quote Link to comment Share on other sites More sharing options...
mike stehr Posted March 7, 2003 Share Posted March 7, 2003 I was just going to post that if Craig had those OPT's on a bench with a scope, AC voltmeter and a frequency generator, he could figure out the primary and secondary impedances, bandwidth, etc... It isn't that difficult. Well, for me it is. I watched the guy I know do it with a pair of Tandberg SE 6BQ5 OPT's that I bought that had unknown specs. (Geez,I really should take notes when I visit this guy.) I'm sure Mark can explain. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted March 7, 2003 Share Posted March 7, 2003 I need to get a scope! I know someone (my father!) who has more than one...maybe he'll sell me of 'em. I don't even know how to use one, though...all I've worked with in every way possible is my trusty old Fluke (also a hand-me-down)meter. I have a signal generator for tuner alignments, but not a scope. It would be great in chasing down problems, too! The custom-wound transformers notwithstanding (probably just the OPTs), Mark (is that the designer's name) should still provide you with a schematic as a courtesy. That said, I guess there are probably more companies that DON'T offer schematics of products as there are that do. Good Luck! Erik Quote Link to comment Share on other sites More sharing options...
Deang Posted March 7, 2003 Share Posted March 7, 2003 I want Craig to figure out how to turn a Scott 299B into a pure Class A amp --that's where the magic really is. Quote Link to comment Share on other sites More sharing options...
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