Erik Mandaville Posted January 5, 2005 Share Posted January 5, 2005 Mark said what I was going to offer -- that regulation and rectification are not the same thing. Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 5, 2005 Share Posted January 5, 2005 Sorry guys, I'm new at this. What's LOL? My electronics experience is in SS, automotive, and scientific instrumentation. This leaves precious little knowlege of tube tech. Are you really going to make me go to a library? Six months in the lab can easily save you a couple of hours in the library! Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 5, 2005 Share Posted January 5, 2005 I remember when I asked that same question years ago! LOL! Did you hear the one about the little fish that swam into a wall, hit his head, and said "Damn!" LOL! Do you understand? It's a funny joke! LOL! It's a way of letting others know you thought something they said was funny! ...like a tree falling in the forest when there isn't anyone around to hear it fall! in that particular case it might be something like, "Help! I'm FDWAC!" (Falling Down With A Crash!) Quote Link to comment Share on other sites More sharing options...
Deang Posted January 5, 2005 Share Posted January 5, 2005 The one that used to get me is FWIW. WTF? I should have known better than to attempt saying something intelligent about amplifiers. Quote Link to comment Share on other sites More sharing options...
garymd Posted January 5, 2005 Share Posted January 5, 2005 I could never figure out YMMV. WTF? Quote Link to comment Share on other sites More sharing options...
Deang Posted January 5, 2005 Share Posted January 5, 2005 rotflolpimp Quote Link to comment Share on other sites More sharing options...
garymd Posted January 5, 2005 Share Posted January 5, 2005 ---------------- On 1/5/2005 7:43:03 PM DeanG wrote: rotflolpimp ---------------- I needed my daughter to tell me what the pimp meant. Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted January 5, 2005 Share Posted January 5, 2005 Damn, did this thread just jump the shark or what? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 5, 2005 Share Posted January 5, 2005 I'm soiled. Soil me... Now say if someone wants to convert a rectifier tube power supply to a SS rectifier bridge or whatever, using the original tube rectifier PS transformer. Can most PS xformers designed for tube rectification, be able to handle a SS bridge and the filtering necessary to get the ripple to a minimum? Or would one be better off to use a PS xformer that would be designed and conform to SS rectifier circuits? Or wouldn't a PS xformer designed for tube rectification put out less current required for a HV SS bridge, and the filtering involved? In Fini's case he has PS xformer's designed for tube rectification, so it would be easier to him (and on the transformers) to convert his Dynaco amps back stock tube rectification. Unless he wants to take a crack course on DC SS power supplies.(Might as well go for SS regulation as well, then.) The bass should still float his boat with the Khorn's, unless he's into hip-hop or something, then he'll need a subwoofer. If I was Gregg, that's what I would do. If you mess with the break points for the coupling caps in a amplifier where stages couple, you can throw phasing off and make a oscillator. I found that out. Simple math goes a long way..... Quote Link to comment Share on other sites More sharing options...
64 Thunderbird 390 Posted January 6, 2005 Share Posted January 6, 2005 There are subtle differences between the two (tube and solid-state rectification), but no differences that would result in audible detection IF properly executed. The subtle differences involved include foward resistance values, foward voltage drops, conduction time, and artifacts caused by the rectification device itself. A tube rectifier is a fairly inefficient device, typically dropping 20V or greater per plate, which results in the need for a higher voltage transformer. It also has a somewhat limited lifespan and has definite limitations on current handling and input capacitance. A silicon diode is a very efficient device, dropping a mere 0.7V, just enough for the diode to conduct. The foward resistance is far less than with the tube, thus the low foward voltage. If used properly, and within limits, both do the exact same job. The silicon diode does produce one artifact in it's output that does not exsist in tube rectifiers, and that is a high frequency noise (hash). The hash is produced from the PN switching action of the diode. It is easily filtered using small value capacitors. It is a type of RF noise that if not filtered, can be detected in the PS or amplification stages by means of an oscilloscope. The noise is beyond the range of the audio band, and is not detectable by the human ear. It can however, have an effect in RF devices such as FM tuners if not filtered out. Any artifacts produced by a rectification device will be removed by the filtering stages for all practical purposes. Either is suitable for audio use. Filtered DC is filtered DC, and no difference could result from the use of a tube or silicon diode in a power supply with similar voltage, current, inductive, and capacitive values. It is also a myth that power tubes are "cathode stripped" by the fast rise time of solid-state circuitry as compared to the slower warm-up of tube circuitry. Applying a plate potential to an *audio* tube before it is warmed up has no adverse effect on that tubes lifespan or operation. The only real concern of using a silicon diode in place of a tube rectifier is voltage compensation and instant voltage output on filter capacitors. These two factors must be carefully reviewed before making any conversions to power supply topology. -Ryan Quote Link to comment Share on other sites More sharing options...
ben. Posted January 6, 2005 Share Posted January 6, 2005 ---------------- On 1/6/2005 12:09:10 AM 64 Thunderbird 390 wrote: There are subtle differences between the two (tube and solid-state rectification), but no differences that would result in audible detection IF properly executed. The subtle differences involved include foward resistance values, foward voltage drops, conduction time, and artifacts caused by the rectification device itself. A tube rectifier is a fairly inefficient device, typically dropping 20V or greater per plate, which results in the need for a higher voltage transformer. It also has a somewhat limited lifespan and has definite limitations on current handling and input capacitance. A silicon diode is a very efficient device, dropping a mere 0.7V, just enough for the diode to conduct. The foward resistance is far less than with the tube, thus the low foward voltage. If used properly, and within limits, both do the exact same job. The silicon diode does produce one artifact in it's output that does not exsist in tube rectifiers, and that is a high frequency noise (hash). The hash is produced from the PN switching action of the diode. It is easily filtered using small value capacitors. It is a type of RF noise that if not filtered, can be detected in the PS or amplification stages by means of an oscilloscope. The noise is beyond the range of the audio band, and is not detectable by the human ear. It can however, have an effect in RF devices such as FM tuners if not filtered out. Any artifacts produced by a rectification device will be removed by the filtering stages for all practical purposes. Either is suitable for audio use. Filtered DC is filtered DC, and no difference could result from the use of a tube or silicon diode in a power supply with similar voltage, current, inductive, and capacitive values. It is also a myth that power tubes are "cathode stripped" by the fast rise time of solid-state circuitry as compared to the slower warm-up of tube circuitry. Applying a plate potential to an *audio* tube before it is warmed up has no adverse effect on that tubes lifespan or operation. The only real concern of using a silicon diode in place of a tube rectifier is voltage compensation and instant voltage output on filter capacitors. These two factors must be carefully reviewed before making any conversions to power supply topology. -Ryan ---------------- Yup. Who needs ears when you've got theory? Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 6, 2005 Share Posted January 6, 2005 "The only real concern of using a silicon diode in place of a tube rectifier is voltage compensation and instant voltage output on filter capacitors. These two factors must be carefully reviewed before making any conversions to power supply topology." And this is why Fini may as well convert his Dynaco's back to tube rectification. I know you can strip a cathode by exceeding heater voltage, it can add a little more emission life with a poisoned cathode if you don't gamble too much with the idea. I did it with a 2.5 volt TJ 300B, for some reason it measured low on emission, the cathode/filament was poisoned or something. Put it on a emission tester and cranked the filament voltage to around 4.5 volts for a half hour, hour. It was at 60%, cooking the filament brought it back to 100% with the other tube. I tested them a month ago, they both were at 100%, though monitoring bias voltage in circuit the tube still bounces around compared to the other. The trick did help, with 200 dollar tubes ya gotta do something... Quote Link to comment Share on other sites More sharing options...
fini Posted January 6, 2005 Author Share Posted January 6, 2005 Could something involved in the conversion to solid state rectification been the cause of one of the power transformers pooping-out in these Mark IVs? I mean something other than a short due to mis-wiring or something stupid like that. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 6, 2005 Share Posted January 6, 2005 If the converter didn't allow for the increased voltage putput from the SS rectifier, it could short the filter cap, burning out the PS tranny. The answer is, yes. Rick Quote Link to comment Share on other sites More sharing options...
Marvel Posted January 6, 2005 Share Posted January 6, 2005 Yo Mike, That little Knight Kit I have does use those little PECs. Not made by Centralab though. They have seven leads and are totally in the tone control circuit. I might just bypass them to get them out of the equation. Marvel Quote Link to comment Share on other sites More sharing options...
NOSValves Posted January 6, 2005 Share Posted January 6, 2005 Marvel, Bypassing the tone control PEC may seem like a easy task but you end up opening a huge can of worms in most cases with a integrated amplifier. Be careful messing around with those PEC's. Craig Quote Link to comment Share on other sites More sharing options...
64 Thunderbird 390 Posted January 6, 2005 Share Posted January 6, 2005 ---------------- On 1/6/2005 9:21:42 AM fini wrote: Could something involved in the conversion to solid state rectification been the cause of one of the power transformers pooping-out in these Mark IVs? I mean something other than a short due to mis-wiring or something stupid like that. ---------------- I think it could be a distinct possibility. The excessive no-load voltage present at turn-on (before the output tubes conduct) would've been extremely high, perhaps 50V higher on the input filter capacitors. Electrolytic capacitors are delicate in design, each being rated at a certain WVDC (working voltage DC) rating. When the rating is exceeded, the aluminum oxide dielectric, as well as the insulating electrolyte, will be overstressed and begin to break down. Once this occurs, you have a leakage resistance that develops across the plate structures of the capacitor. If this leakage resistance drops too low, the power supply will "load down", as it cannot supply enough current across the leakage resistance. If not caught early, the HT secondary of the transformer will be destroyed (short or opening of that winding). The overvoltage itself is not the failure mechanism, but the damage it causes to associated devices is. Any item designed to run tube rectification should use tube rectification. The one major advantage of using a tube setup is the delayed warm-up time of the cathode, resulting in a gradual increase of B+ to the filter capacitors. Tube rectifiers come in two main types, directly heated and indirectly heated. The 5U4 is directly heated, and has a warm-up time of about 7 seconds. The 5AR4 is indirectly heated, and has a warm-up time of about 11 seconds. Both have a sufficient delay in voltage output at the cathode. A silicon diode turns on instantly. -Ryan Quote Link to comment Share on other sites More sharing options...
64 Thunderbird 390 Posted January 6, 2005 Share Posted January 6, 2005 ---------------- On 1/6/2005 12:59:17 AM mike stehr wrote: I know you can strip a cathode by exceeding heater voltage, it can add a little more emission life with a poisoned cathode if you don't gamble too much with the idea. I did it with a 2.5 volt TJ 300B, for some reason it measured low on emission, the cathode/filament was poisoned or something. Put it on a emission tester and cranked the filament voltage to around 4.5 volts for a half hour, hour. It was at 60%, cooking the filament brought it back to 100% with the other tube. I tested them a month ago, they both were at 100%, though monitoring bias voltage in circuit the tube still bounces around compared to the other. The trick did help, with 200 dollar tubes ya gotta do something... ---------------- It does work with certain tubes, Mike. I have sucessfully done this with 2A3's, 45's, 300-B's, 12AX7's, and a few other tubes. The important thing to remember is NOT to apply any test voltages to the tube other than filament voltage. This will not work with most pentodes, and usually results in damage between elements (leakage and shorts). The idea is to renew the spent cathode by bringing new electron emitting material to the surface of the cathode. Often times, it will work well, BUT, the lifespan of the tube is rather short. The process works best with large thoridated filament tubes, they have a more robust cathode. Typically, for the smaller tubes like 2A3, the bias voltage must be reduced significantly to receive the same power output as compared to a new tube. The renewed cathode is not as powerful and requires less opposition by negative grid voltage. -Ryan Quote Link to comment Share on other sites More sharing options...
64 Thunderbird 390 Posted January 6, 2005 Share Posted January 6, 2005 ---------------- On 1/6/2005 10:14:06 AM Marvel wrote: Yo Mike, That little Knight Kit I have does use those little PECs. Not made by Centralab though. They have seven leads and are totally in the tone control circuit. I might just bypass them to get them out of the equation. Marvel ---------------- Most PECS were made by Sprague and Centralab. They are nothing more than resistors and capacitors in monolythic form. Inside are all the components to the equalizer circuit. It is very easy to bypass the tone control PEC if you have the schematic. Be sure also to bypass the associated tone control pots. On a schematic, you will be able to clearly see where the preamp tube plate's output enters the tone control stage, and where the output is to the grid of the next preamp tube. Everything in between is bypassed. The plate output of V1 to the grid of V2 must be capacitor coupled. The PEC on a schematic is notated by the use of broken lines surrounding the PEC components. It is also possible to build a discrete stage and remove the PEC. -Ryan Quote Link to comment Share on other sites More sharing options...
yaffstone Posted January 6, 2005 Share Posted January 6, 2005 The tube filaments are tungsten with thorium added to lower work function. The work function is the amount of energy you have to empart to an electron to convince it to leave its atomic orbital and become part of the current flow of the circuit. If the surface of the filament gets poluted or if the filament gets too hot, the throium can be blocked or blown off respectively. Heating the filament hotter causes imbeded throium to travel to the surface where it can act as a lower energy emitter again, replacing that which was there first. Impurities could also be boiled off, condensing on the cooler glass. This is the physical chemist's explanation for why over heating within reason can revive a tube. Quote Link to comment Share on other sites More sharing options...
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