Deang Posted January 7, 2004 Author Share Posted January 7, 2004 I've been comparing the Quad II schematic to the one for the II-forty I got in the mail today. The layout is identical. You could lay one on top of the other, hold it up to the light, and they would look exactly the same with the exception of the values. Sure sounds damn good for staight pentode. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 8, 2004 Share Posted January 8, 2004 Craig, in the attached schematic to run this Dynaco in quasi triode mode: 1)Disconnect the ultralinear tap from the grids of the 4 output tubes. 2)install a 100ohm resistor between the plate and grid to supply propper voltage to the grid for the power beam. Presto triode sound albiet with half the power but smooth as silk. Rick Did I say that this Scott sounds good? Quote Link to comment Share on other sites More sharing options...
Deang Posted January 8, 2004 Author Share Posted January 8, 2004 Just found this: "The Quad lI's circuit is quite interesting. The amplifier has only two stages, hence it requires 1.4volts of input signal to produce its 12watt output, and so must be used with some kind of pre-amplifier. A quick mod for a little more gain is to use a 470hm resistor instead of the 100ohm one located on the cathodes of both the EF86s. This results in a dramatic increase in sensitivity, with no real compromise in sound quality. You will still need to find 600millivolts (0.6volt), so a pre- amp is called for. The output transformer is unusual in that it incorporates a cathode winding as well as the usual anode windings. This applies an 'out of phase' signal to the transformer and helps it produce triode-style impedance from two tetrodes, with the advantage of only needing the same drive voltage. The disadvantage is that the output valves are running quite a bit harder than the 12watt power rating would suggest. If you were being cruel to a Quad II, you could point out that a Leak Stereo 20 has a larger output transformer, and to be honest, the basic 'guts' of the Leak are way better. But thanks to some clever trick with resistors within the transformer case, the Quad II gets away with it. Sound-wise, the Quad is one of the finest amps from its period. It is clean, sweet and very load tolerant (the ideal partner for the Quad Electrostatic Loudspeaker)... It is very hard to describe the Quad sound - it is what the amp doesn't do that is more noticeable. When all original, it has a magic, open sound that very few amplifiers can compete with. On the flip side, the bass is a bit warm, and when driven into overload, it can bounce about all over the place. But then this is classic valve-amp behaviour. Because of this soft, bouncy limit, stick with efficient loudspeakers - Klipsch and Lowthers are ideal matches (Quad lls with Klipsch La Scalas are awesome!), and don't forget a good pre-amp." -------------------------------------------------------------------------------------------------------------------------------------------------- Of couse, the II-forty is a bit of a different animal, but still, some good info. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 8, 2004 Share Posted January 8, 2004 Looks the same as this. Rick Quote Link to comment Share on other sites More sharing options...
Deang Posted January 8, 2004 Author Share Posted January 8, 2004 I think what you're calling Quasi-Triode we call "strapped in triode". Craig has done this several times, and is actually running his MK III's this way now. What you are saying about the Quads makes sense. Mike Sanders gets 80wpc out of two KT-88s -- and the Quads are putting out forty with the same two tubes. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 8, 2004 Share Posted January 8, 2004 "I think what you're calling Quasi-Triode we call "strapped in triode". Craig has done this several times, and is actually running his MK III's this way now." Yea, that's what I'm talking about! But no more tonight. Time for my beauty sleep. Did I say that this Scott 299c with NOS parts is sounding sweet tonight? I hate to turn it off. Rick Quote Link to comment Share on other sites More sharing options...
neo33 Posted January 8, 2004 Share Posted January 8, 2004 Those are nice and fancy "heaters", Deano. I can make good use of them during this cold winter . PS. I am not a Freak! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 8, 2004 Share Posted January 8, 2004 Rick, You don't understand Triode operation of a Pentode or tetrode!! Triode is tapped off the Plate feed after the B+ goes throught the output transformer. The voltage is derived from the plate and in all reality your directly connecting the plate to the screen. In Deans amp the Screen is directly fed from the B+ this is normal everyday Pentode just like your Scott ! Nothing Triode about it. The only difference is your Scott doesn't have a Choke power supply and uses a Resistor to drop the voltage to the screen. Trust me this is Pentode. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 8, 2004 Share Posted January 8, 2004 Looks the same as this. Rick What looks the same ?? That is straight out Ultra Linear ! Rick trust me I have strapped amp in triode a billion times. Your like the student trying to teach the teacher here LOL !! You know I do thios stuff for a living I'm not saying I can't learn but geezzzz Quote Link to comment Share on other sites More sharing options...
Deang Posted January 8, 2004 Author Share Posted January 8, 2004 It can't be a pentode -- it's using tetrodes. Quote Link to comment Share on other sites More sharing options...
maxg Posted January 8, 2004 Share Posted January 8, 2004 "It is clean, sweet and very load tolerant (the ideal partner for the Quad Electrostatic Loudspeaker)... It is very hard to describe the Quad sound - it is what the amp doesn't do that is more noticeable. " Ideal partner for the Quad Electrostatic speaker? Hmmm. Well that wasnt my experience with the thing. It was sweet enough but didnt have the balls to drive them. You are definitely better off with the Khorns. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 8, 2004 Share Posted January 8, 2004 "It can't be a pentode -- it's using tetrodes" Rick Craig, We both have a lot to learn. I meant the second schematic above of a mark III is the same circuit type as the SCA 35 just easier to see. The plate of Dean's amp is connected through the OPT. B+ is at the top the plate is connected to the bottom. Rick Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 8, 2004 Share Posted January 8, 2004 Rick you have completely lost me ! This is Pentode wired strangely but still Pentode Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 8, 2004 Share Posted January 8, 2004 If I were to wire my Stereo 35 (Dynaco clone) ultralinear amp in triode mode, I would strap the plate to the screen grid with a 100 ohm resistor to apply voltage. In Deans amp the grid is tied to the plate through an L/C circuit to drop and apply the voltage. In a Scott the screen grids are connected directly to the power supply.(425V on a 299D late) The Scott is in classic pentode mode, Deans is something different. Rick Edit: That's why I asked Mark to jump in here. He's probably laughing his a$$ off at us right now. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 8, 2004 Share Posted January 8, 2004 No it isn't !! Just because there is a choke in place of the resistor doesn't change what it is! A choke acts as a resistor but also smooths out the B+. I installed a choke in place of the first dropping resistor in my Scott 208 power amp so now is it something other then a pentode ?? I think not Geezzzz Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 8, 2004 Share Posted January 8, 2004 "I installed a choke in place of the first dropping resistor in my Scott 208 power amp so now is it something other then a pentode ?? I think not Geezzzz" No, You have created an LCR power supply. However if you disconnected the voltage to the screen grid from the power supply and connected a proper value resister from there to the plate, you would be running in what Dean called "strapped triode" and I called "Quasi-triode. Like you are running your Mark IIIs. Rick Quote Link to comment Share on other sites More sharing options...
Deang Posted January 8, 2004 Author Share Posted January 8, 2004 Hey Craig, take a valium. Rick's just trying to be helpful. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 8, 2004 Share Posted January 8, 2004 Dean, Get off the moderator kick dude !! What did I say to deserve that ?? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 8, 2004 Share Posted January 8, 2004 He is wrong that is all. I'm trying to help here too ! But forget it geeezzzzz Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted January 8, 2004 Share Posted January 8, 2004 ---------------- On 1/8/2004 11:54:27 AM 3dzapper wrote: "I installed a choke in place of the first dropping resistor in my Scott 208 power amp so now is it something other then a pentode ?? I think not Geezzzz" No, You have created an LCR power supply. However if you disconnected the voltage to the screen grid from the power supply and connected a proper value resister from there to the plate, you would be running in what Dean called "strapped triode" and I called "Quasi-triode. Like you are running your Mark IIIs. Rick ---------------- Rick, The filtering cap (C4) "decouple" the screen grid from the PSU. It is not strapped triode or quasi-triode as you call it. Quote Link to comment Share on other sites More sharing options...
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