3dzapper Posted October 4, 2004 Share Posted October 4, 2004 Well!! There goes that theory right out the window!!!! Rick Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 4, 2004 Share Posted October 4, 2004 ---------------- On 10/4/2004 6:54:00 PM 3dzapper wrote: Craig, The max according to the Amperex chart at 500V is 60uF with a 150ohm snubber resistor on each cathode. http://www.triodeel.com/5ar4_p1.gif Without the current limiting resistor Hafler used 30uF@525VDC in the Mark III design. It has been widely reported that the Mark III can spike to approximately 550VDC on start-up so the 525 volt rated capacitor is inadequate. In my experiments, I have toasted a 5AR4 with 107uF. Pretty blue sparkes inside the envolope. Too bad I had the lights on. The termination of the red transformer wire is at the PS capacitor in the above schematic. The 6800 ohm resistor would have to be mounted on the output of the switch. Rick ---------------- Oh now your adding the 6.8K reisistor. Rick all I'm saying here is you need to not give advise if your not going to be complete before you know it you will feel pretty bad when someone screws there amp up or damages some nice tubes. Your still not taking the increased voltage that the first filter section is going to be presented with absolutely no current draw in the amp. The 5AR4 is a slow start tube having a stand by switch is not worth the effort. Once again I will repeat 100uF will not toast a 5AR4 in GOOD working order. Craig Quote Link to comment Share on other sites More sharing options...
R. Inman Posted October 4, 2004 Share Posted October 4, 2004 ---------------- On 10/4/2004 6:39:05 PM 3dzapper wrote: Craig, If you put a 100uF cap accross the rectifier in a MarkIII you will essentially have a dead short accross that tube for just under .1sec. There is no snubber resistor between the cathode of the 5AR4 and the first cap to make a current ramp. http://forums.klipsch.com/idealbb/files/mark3sch.jpg" border="0"> Tom said that he modded his Mark IIIs himself. I am assuming that he took all the advice on the web and upgraded the PS cap. If not, he should take 2 47uF@450VDC caps connected in series (23.5uF@850VDC) and place them in front of the choke. Then he can place additional capacitance after the choke like 2 sets of 2 330uF@450VDC(2 X 165uF) in series to the red OPT wire. Have you never heard of a stand-by switch on an amplifier? That is what I recommended above. Look at the schematic. The switch would be placed in such a locattion that no (zero!) voltage would be applied to the plates of the 6AN8. Rick ---------------- Very correct, Rick. For all practical purposes, you would have a short circuit on the 5AR4 cathode immediately after turn-on. 100 uF without a series choke or resistor is asking for trouble. The absolute maximum is 60 uF, and most conservative designers would never push the 5AR4 even this much, 40 uF was typical. 100 uF with no series resistance presents a reactance of 13 Ohms, far too low of a safety margin. What is the value of that choke? Knowing this value can tell you how much capacitance can be added *safely* after the choke. The best place for the stand-by switch would be in series with the power transformer secondary center-tap. No CT = No voltage, very simple to implement. I do not care for series electrolytic capacitors, as most are not perfectly matched for tolerance, and can lead to an imbalance *if* a series compensation resistor is not used. Your concern about the 5AR4 maximum input capacitance is a wise one. Best regards, Ryan Quote Link to comment Share on other sites More sharing options...
Piranha Posted October 4, 2004 Share Posted October 4, 2004 No wonder my 5AR4's took a sh!t. Quote Link to comment Share on other sites More sharing options...
ShapeShifter Posted October 5, 2004 Share Posted October 5, 2004 A view on tube logos, labels and manufacturer. http://www.tube-classics.de/TC/Tubes/Valvo/Philipstubes.htm Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 5, 2004 Share Posted October 5, 2004 Not all designers safety margins are the same ! Hence the words "Design Center line" All that is required to insure your not absolutely frying the rectifier are some DC current measurements and AC ripple calculations. Design Center lines are not a "absolute" the final judge is real world operation. Craig Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 5, 2004 Share Posted October 5, 2004 ---------------- On 10/5/2004 10:56:11 AM ShapeShifter wrote: A view on tube logos, labels and manufacturer. http://www.tube-classics.de/TC/Tubes/Valvo/Philipstubes.htm ---------------- Very cool link ! Quote Link to comment Share on other sites More sharing options...
ben. Posted October 5, 2004 Share Posted October 5, 2004 Craig, Check your mail , please & let me know what you think when you get a minute. Thx, Ben Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 5, 2004 Share Posted October 5, 2004 Just replied ! Quote Link to comment Share on other sites More sharing options...
Rickieheinz Posted October 5, 2004 Share Posted October 5, 2004 you may want to check out the tube website, tube asylum. I've hard that electroharmonix (in el34's) has a sound that is like the mullards at a fraction of the price. Quote Link to comment Share on other sites More sharing options...
R. Inman Posted October 5, 2004 Share Posted October 5, 2004 Amperex 5AR4 data sheet: http://www.triodeel.com/5ar4_p1.gif There is a bit of confusion over the terms "design center value" and "maximum values". Both mean "worst case operating conditions", as is the new term given to semiconductor devices. They all have the same meaning, they are values given as an absolute maximum, used under the absolute worst design conditions. If these values are exceeded, does that mean the tube will fail? Not necessarily, but it surely will not last as long. There are electrical components made for every application, and to use one well in excess of it's rated maxmium values is not wise. 5AR4 is a good tube, but like anything electrical, has its limits. 60 uF with a limiting resistor is the tubes limit into a first stage RC filter. There is no reason to exceed 60 uF on the Dyna design, the only outcome would be added stress to the 5AR4 and an increased E-Avg on the first filter capacitor stage. Notice that the designer has chosen to use 30 uF, 1/2 of the 5AR4's limit. There is no performance "boost" from raising this value. The choke and capacitors located after the choke will do the "work" of providing filtering and power supply "stiffening". Since the choke provides immense opposition to current, the capacitors following the choke can be much larger, as the choke effectively "isolates" the rectifier cathode from the capacitive load. Best regards, Ryan Quote Link to comment Share on other sites More sharing options...
R. Inman Posted October 5, 2004 Share Posted October 5, 2004 Nice post, Mark One question if you don't mind: Since this amplifier uses a choke, what would be the benefit of increasing C1 from 30 uF to 100 uF? In my opinion, any sonic gain would be minimal, if not insignificant. If a designer wanted to increase some capacitance, why not do it after the choke, away from the 5AR4 cathode? The 30 uF value seems "sufficient" to me, why increase it and strain the tube? -Ryan Quote Link to comment Share on other sites More sharing options...
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