bb50e2e7   
   From: none@ntlworld.com   
      
   On 08/09/2010 05:34, arthrnyork@webtv.net wrote:   
   > On Sep 7, 7:31 am, Patrick Turner  wrote:   
   >> On Sep 6, 12:55 am, Richard  wrote:   
   >>   
   >>> On 05/09/2010 12:33, Patrick Turner wrote:   
   >>   
   >>>> Most people have utterly no clue about what the tube tester tests   
   >>>> mean.   
   >>   
   >>>> Patrick Turner.   
   >>   
   >>> Let's just say that I wanted to make a dedicated tube tester for my   
   >>> KT88's. Not just test the tubes, but to enjoy the experience.   
   >>   
   >> Well, feel free to enjoy the experience.   
   >>   
   >> Tube testers used to be a common peice of quite expensive test gear   
   >> owned by service dudes.   
   >>   
   >> If a television arrived on their bench they could test all 27 vacuum   
   >> tubes to see if they were serviceable within an hour.   
   >> The alternative was difficult because it involved lots of probings of   
   >> the working circuit and use of much other gear and the analysis took   
   >> much longer.   
   >>   
   >> But audio circuits are dead simple compared to much other TV circuitry   
   >> operating at RF and with weird signals within.   
   >>   
   >> Now that nearly all service ppl have retired, expired, died, their   
   >> piles of old test gear are for sale as old cheap junk ( if their   
   >> surviving wives have not chucked it all in the dumpster bin ). Not   
   >> many folk value the old junk, except for some audio amateurs or   
   >> audiophiles who can afford such junky old gear which sells for a price   
   >> that is a tiny fraction of the real cost of the unit in 1960.   
   >>   
   >>> Okay, let's take this step by step and let's just concentrate on each   
   >>> step. Let's just deal with steps 1 and 2 for now.   
   >>   
   >>> Of course, if the tube is faulty it may turn up in the early stages of   
   >>> testing and testing would stop early on.   
   >>   
   >>> STEP 1: Measure heater continuity.   
   >>   
   >>> If an open condition - stop testing.   
   >>   
   >> A DMM can test the heater continuity faster than you can say "vacuum".   
   >>   
   >>   
   >>   
   >>> STEP 2: Electrode leakage (Cold). If failure stop test.   
   >>   
   >> This is unusual. Usually leakage mostly happens when a tube is   
   >> heated.   
   >>   
   >>> What electrodes are tested? And what voltages? AC or DC?   
   >>   
   >> When testing any audio tube in a circuit prepared for the purpose or   
   >> in an existing amplifier all electrode voltages applied are recorded,   
   >> both Vac and Vdc, and all current flows anywhere are analysed and   
   >> recorded. This is done in a manner where the person testing is on   
   >> guard for any wayward tube conducting too much current anywhere. So   
   >> one has to learn to be alert and measure the rise of cathode currents   
   >> right after turn on and all test circuits should feature suitable   
   >> sensitive fuse values to protect the testing circuits and PSU from   
   >> undue stress, and most certainly against the antics of a bamboozled   
   >> audiophile wondering just why the power tranny of his tester PSU or   
   >> precious amplifier is getting do damn hot.   
   >> After some practice, with some possible clouds of smoke and fused test   
   >> gear parts, the audio amateur might get to understand what he is   
   >> testing and what he is doing so that when he probes or measures   
   >> anything, he KNOWS what he SHOULD SEE on his meters and on his CRO,   
   >> ( oscilloscope ).   
   >>   
   >> Electronics testing is a great teacher of mental discipline and   
   >> applied logic, and one should learn to ask many questions of the gear   
   >> and of yourself and to never assume anything. Departure from   
   >> discipline leads to smoke.   
   >>   
   >>   
   >>   
   >>   
   >>   
   >>> a) Heater to Cathode (What Voltage?)   
   >>   
   >>> b) Cathode to G1 (What voltage?)   
   >>   
   >>> c) Cathode to G2 (What voltage?)   
   >>   
   >>> d) Cathode to G3 (What voltage?)   
   >>   
   >>> e) Cathode to Anode (What voltage?)   
   >>   
   >>> etc.   
   >>   
   >>> I'm not actually sure which electrodes should be tested in relation to   
   >>> other electrodes. I believe some electrodes would be connected together   
   >>> in the leakage tests. Anyone know all about the leakage part of testing?   
   >>   
   >>> Can anyone give me an idea of a suitable circuit (components) just to   
   >>> test KT88's for leakage? A circuit that protects a meter.   
   >>   
   >>> After leakage is sorted, then I can go to another specific step in testing.   
   >>   
   >> Leakage is only one thing might worry about before, during and after   
   >> one tests a given OP tube.   
   >>   
   >> All the other basics must be learnt.   
   >>   
   >> I started by building a preamp from scratch but froma circuit a good   
   >> bloke I knew gave me. Then I found myself asking 1,001 questions and I   
   >> could not rest easily unless the full answers came as a result of   
   >> reading good books on tube audio and carrying out experiments in my   
   >> shed behind my house for a couple of year fulls of frustration and   
   >> very late evenings.   
   >>   
   >> I acquired the shelf of good books, and I done my home work, and all   
   >> before ever getting a PC and talking about the learning process with   
   >> others. I just DID IT.  I moved onto repairing giutar amps for a   
   >> couple of years and this taught me about every possible way a vacuum   
   >> tube could misbehave.   
   >>   
   >> But musicians are always broke, and I had had a dream about my future.   
   >> I dreampt I would get to know all there was to know about tubed audio   
   >> gear and that I would build and sell new gear second to none   
   >> elsewhere. So I soldered onwards, and I am still learning, although   
   >> sometimes I think now I am trying not to forget what I have begun to   
   >> understand, before I become senile, or before my hard drives crash yet   
   >> again, and take with them a nice new website page which is better than   
   >> one I have aleardy established.   
   >>   
   >> Unless an audiophile has a visionary mission plan he may dither around   
   >> and never seem to get anywhere. I know guys who have made large   
   >> complex stereo systems with 4 amplifiers per channel and with active   
   >> crossovers and they are constantly changeing things and they   
   >> constantly complaining about noise and distortion and bad channel   
   >> balance and they don't want to spend money on a tradesman to fix   
   >> things and even after 5 years they cannot use a digital voltmeter and   
   >> nor do they seem to have the ability to think about things concisely   
   >> or logically. I recall the joke about Californians. "How is a light   
   >> bulb changed in Carlifornia?" Well, it takes 20 people gathered for a   
   >> happening and a pile of LSD tabs, and man, wow, what an experience -   
   >> especially when the house caught fire.   
   >>   
   >> Testing a KT88 is not rocket science and not terribly dangerous IF ONE   
   >> TAKES PRECAUTIONS.   
   >>   
   >> But one has to gradually work up to testing a KT88, IMHO.   
   >>   
   >>   I would suggest those interested should first spend time with basic   
   >> transistor circuits using supply rails less than +/- 40Vdc. Build a   
   >> preamp. Get it working. Analyse why it works. find out why the first   
   >> three transistors you connected failed and fused so easily. Write out   
      
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