B&K Dyna-Quik 500 shows good tubes as Shorted

[BmWr75]

I bought this tester today, she's not pretty, but supposedly works. It shows every 12AX7/12AU7/12AT7 as Shorted, even ones I know are good (e.g., tubes bought recently from Jim McShane).

Saw another one of these that sold on Headfi.org that had the same problem. Any one got any ideas why the false Short results are happening? Might it have something to do with the 3 aging polar electrolytic caps under the socket board? I ask because IIRC the Short light doesn't light up immediately.


Follow up question - The 6DJ8 tube is not listed on the tube sheet inside the top lid (or a 6BQ5 for that matter). Does anyone know how these two tube types can be checked with this model tester?

[TheGimp]

IF you don't have a manual, here is a link.

http://www.jogis-roehrenbude.de/Roeh...500_manual.pdf

First I'd replace any old electorlytics, then I would start with the circuitry around the Neon Short Bulb and measure each component to look for an out of tolerance/bad part.

There is not a whole lot to go wrong in a tube tester.

Good luck.

[HollowState]

Excessive internal leakage from humidity and moisture will cause an early short condition as will out of tolerance componets. Also be aware that dual triodes like the 12AX7 are tested with their sections in parallel. Apparently to save time and cost. Here is some info I found on this forum.

David Campbells instructions:
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Signal Voltage adjustment (Test Switch in Gm position)
Set to 1.0 volt AC at terminal 5 of the wiring block on the top section of sockets to terminal 1 (gnd), Terminal 1 is most near socket 7. The terminals are numbered 1 through 12 on the schematic. This AC voltage is adjusted by R-14 which has yellow, black and orange wires attached, and mounted left of another Potentiometer when the meter is facing you under the top section of sockets mounted to the bottom of the tester. Terminal 5 is the low bias -2.5VDC voltage terminal, i.e. at that terminal you have both a DC bias and an AC signal voltage. See the following pictures for Terminal and Pot locations.
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DC BIAS Adjustment (Test Switch in Gm position)
Proper DC bias at terminals 5, 6, 7 to terminal 1 (gnd) is accomplished by adjusting the R-9 potentiometer which is positioned just right of R-14. Set a voltmeter to DC volts; connect between terminals 5, to gnd (set this voltage to -2.5VDC, terminal 6 and 7 voltage adjustment is done when terminal 5 is set.

Terminal 5 is -2.5volts, Terminal 6 is -7.5 volts, Terminal 7 is -13.0 volts
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Balance Control Adjustment (Test Switch in Gm position)
Connect a 6k ohm 10 watt resistor between terminal 10 (plate) and terminal 1 (gnd) with Sensitivity Control set to 100. Adjust R-19 so that you get zero reading on the tube tester meter. R19 access hole is left of the 6AT6 tube under the top section of sockets.
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Short Sensitivity (Test Switch in Short position)
I don’t see any adjustment for this (No more Pots). You can check to see if it’s working by inserting a 1 Meg ohm resistor between pins 2 and 4 of socket 7A and looking at the shorts lamp. This lamp must be a NE-51 for the circuit to work properly.
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Gas Sensitivity (Test Switch in Gas position)
Again, I don’t see any adjustment for this (No more Pots again). You can check this by inserting a 20 Meg ohm resistor between pins 1 and 2 of socket 7A and seeing the meter move to about 2000 on the black Gm scale. On my tester, the reading was about 1800.
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Filament Voltage Check
I checked each of the voltages for the filaments with no tubes installed first. They were each slightly higher then the settings. I then checked the 6v setting with a 5881 tube which takes about .9 amps of heater current. I measured 6.1 volts, which indicates that the transformer is working well.

[BmWr75]

Thanks guys.....I'll start by replacing the 5 electrolytic capacitors.

[BmWr75]

Originally Posted by HollowState

------------------------
Short Sensitivity (Test Switch in Short position)
I don’t see any adjustment for this (No more Pots). You can check to see if it’s working by inserting a 1 Meg ohm resistor between pins 2 and 4 of socket 7A and looking at the shorts lamp. This lamp must be a NE-51 for the circuit to work properly.

Hollow State,

The operating manual for the 500 tester says this lamp must be a No. 44. Are you certain this calibration procedure is for a B&K Dyna-Quik 500? I searched the Tube forum and couldn't find the post that contained this info.

[HollowState]

B&K 500 Tube Tester Calibration
Short lamps are almost always neon.

Edit: I just looked in the downloaded PDF manual. Page 9 of the testing instructions says the short lamp is a neon. The schematic shows a neon lamp as does the parts list. This may be your whole problem. Use an NE51.

[HollowState]

These early B&K testers used three #44 incandescent lamps. One as the pilot and two more in the Gm balance circuit underneath. In normal operation the two in the balance circuit will both light up dimly when a tube is tested. Since both the base and bulb type are the same for a 44 and NE-51, it is easy to mix them up if you look quickly at them. Be assured that the short lamp is a neon.

[BmWr75]

Originally Posted by HollowState

These early B&K testers used three #44 incandescent lamps. One as the pilot and two more in the Gm balance circuit underneath. In normal operation the two in the balance circuit will both light up dimly when a tube is tested. Since both the base and bulb type are the same for a 44 and NE-51, it is easy to mix them up if you look quickly at them. Be assured that the short lamp is a neon.

You are correct. My tester has three #44s and one NE-51. I misread the parts list earlier. Sorry about that.

[Joe1944]

I recommend the following link. Go to the picture of the B&K 675 about 2/3 down the page and click the see my collection of B&K testers. At the bottom of that page is information on calibration of B&K 500/550 testers.

Tales From The Tone Lounge; The Idiot's Guide To TubeTesters!

Hope this helps

[BmWr75]

The B&K 500 tester now has all new caps and 44 lamps. This solved the false short problem I was getting on every tube.

Tried the calibration procedure shown in an earlier response, but the potentiometers R( and R14 were frozen. Sprayed them with Deoxit and got them moving. But now they don't make any difference to the voltage readings measured between terminal 1 and 5. The AC voltage is supposed to be 1 volt, but is reading ~10 volts. The DC reading is supposed to be -2.5 volts, but is reading about -1 volt.

Would appreciate it if someone would recommend a new potentiometer I could buy to replace the existing ones. Also, I broke one of the No.44 lamps sockets and have temporarily fixed it. Is there a new lamp socket that can be purchased?