Tube tester calibration/repair

sinisterick · Post by **sinisterick** » Wed Jan 18, 2006 5:44 pm

I have a Hickok 605 tube tester that I cannot get to line adjust. Just cannot get the meter to the proper position no matter how much I turn it up. My guess is one of the two rectifier tubes. Anyone have a more likelier candidate. Anyone have an idea which of the two tubes it is more likely to be? If I could just get it working properly, my amps will rest easier knowing they won't be smoked by some "new" tube.

rictified · Post by **rictified** » Wed Jan 18, 2006 8:37 pm

I am probably wrong but I always thought rectifier tubes either worked or they didn't. Most rectifier tubes are cheap anyway. Hickok are supposed to be nice tube testers.

soundmasterg · Post by **soundmasterg** » Thu Jan 19, 2006 12:53 am

It probably needs to be calibrated. There should be instructions for how to calibrate the tester somewhere on the web. Most of the hickok testers were very similar in how to calibrate them. Try posting this on the webervst and ampage forums and see if anyone more knowledgable can steer you in the right direction.

sinisterick · Post by **sinisterick** » Thu Jan 19, 2006 10:15 am

I was just hoping to not buy a pair of tubes only to find out it is something else. I've done alot of surfing on this and have a schematic and a calibration manual. Step 1 in calibrating is to turn the line adjust knob until the meter reads 120 volts. It does not say what to do if it won't get that high (figures). Tube testers are very critical of the voltage coming into them from the wall, that's why this is adjustable. If you don't have exactly 120 volts, all the voltages going to the tube you are testing will be off and so will your measurements. If I remember my basic electronics class correctly, a rectifier basicly allows current to flow in one direction but not in the opposite direction. Basically it acts as a short (zero resistance) in one direction, and an open circuit (infinite resistance) in the other. I believe that as a rectifier tube gets old the zero resistance direction gains some resistance which causes some voltage to be lost in the rectifier tube itself and doesn't get to all the circuits beyond it. This can be a problem in amplifiers that have tube rectifiers too. Your 100 watt toy may only be putting out 80 due to a shaky rectifier tube that isn't supplying the proper voltage to your your output tubes. As far as testers in general, testers that can measure mutual conductance are the way to go. You can match tubes with this type since they are actually measuring the amplification of the tube. Cheaper testers only test for shorts, leaks etc...they don't really give you an idea how well the tube will perform-you just get a "good" or "bad" rating. Sorry if this has been a long winded lecture-maybe this all interests you, maybe not. I just figured I'd put it out there. One more thing- I'm a newbie here-where on the forum should I show off my 1980 lefty 4001 mapleglow?

ken_j · Post by **ken_j** » Thu Jan 19, 2006 1:57 pm

Welcome Abbott. Yes you should show off your 4001 in the bass section.

Oh yeah, never too late for me to learn something.
Thanks.

rictified · Post by **rictified** » Sat Jan 21, 2006 10:52 am

http://www.vacuumtubes.net/

This is a great place for old obsolete tubes, rectifier tubes are usually pretty cheap. Try checking the input to the tubes and the output with a multimeter, see how much loss you have.

soundmasterg · Post by **soundmasterg** » Sat Jan 21, 2006 4:38 pm

You should be able to do some math to figure out if your rectifier tubes are working up to snuff or not. You take your AC voltage after the power transformer and multiply it with whatever the conversion ratio is for the rectifier tubes you are using. A GZ34 for example is 1.3 times the AC. If you don't have a power transformer in that tester, and the rectifiers are hooked directly to the AC, then you multiply whatever the conversion ratio is for those tubes times the AC line voltage, and that should equal the DC voltage you get out of your rectifiers if they are working correctly. There are many sites around that give the specs for most tube types.

I've got a B & K 747 mutual conductance tester myself. Its prety easy to calibrate, although the scale on the thing is arbitrary and doesn't really mean anything. In order to know if a tube is good or not, you have to have a known "good" one to compare readings with any time you test one. But it works well to weed out the bad tubes, and then I can test the tubes in circuit to see how they really work.

sinisterick · Post by **sinisterick** » Sun Jan 29, 2006 5:38 pm

Thanks Greg- I should be able to handle this and sorry for the delayed response.