4 ms·

I have come across lots of jerks selling bad old tubes ("but my tester featuring unknown principles of operation pointed the needle at the GOOD sector, not the

by kw71 12y ago

I have come across lots of jerks selling bad old tubes ("but my tester featuring unknown principles of operation pointed the needle at the GOOD sector, not the BAD or "?" sectors!" (What kind of instrument has a "?" on the meter face?)) I wonder how the counterfeits would be done today, since the phenolic bases on the old octal tubes probably can't be matched by any material around now.

kazinator 12y ago
>What kind of instrument has a "?" on the meter face? Why, a dashboard designed by Dennis Ritchie. You will have to google that one.
- dietrichepp 12y ago
  > You will have to google that one. It's from The Unix Hater's Handbook, which is worth reading if you like Unix.
dietrichepp 12y ago
> What kind of instrument has a "?" on the meter face? I've seen a few equipment testers with a "?" between "Bad" and "Good". I have a battery tester with this, and tube testers like this are not uncommon. They are typically emission testers, which wire up the tube like a diode, with the grid wired to the cathode. As the tube ages, the cathode coating will wear out and emission will drop. The cathode coating wears out through normal use the same way an incandescent lamp wears out: at normal temperatures, it will evaporate and get deposited somewhere else in the tube. Emission testing is far from perfect, but it's a good first test to figure out e.g. which tube is a dud. I have a hard time caring because I never buy NOS tubes (same reason I don't buy CA3280s).
- kw71 12y ago
  A friend of mine has an emission tester (maybe it can put some signal on the grid - I haven't seen it in a while.) I've got a hickok machine that you look up the grid bias in the chart and can receive a reading in ... micromhos? Ok that implies conductance but that's a strange unit. I'm not sure these are "instruments." My treasure is a machine from soviet russia, it actually uses a signal generator to feed the grid, and measures transconductance in mA/V. It's got a bunch of power supplies, VTVM and microampere meter whose smallest scale resolves some nanoamperes, so I trust its methodology. It's nice to find the actual current passed by a rectifier tube instead of setting a meter bias knob to read out the 'strength' on a unitless 0-100 scale. But I never figured out how to intereperet the "?" on the emission testers. My tube fap shrine won't be complete until I get a Tek 575 though.
  - dietrichepp 12y ago
    I'm not sure why the mho is a strange unit. It is just another name for the siemens (a.k.a. ampere per volt).

by kw71 12y ago

kazinator 12y ago

>What kind of instrument has a "?" on the meter face? Why, a dashboard designed by Dennis Ritchie. You will have to google that one.

dietrichepp 12y ago
> You will have to google that one. It's from The Unix Hater's Handbook, which is worth reading if you like Unix.

dietrichepp 12y ago

> What kind of instrument has a "?" on the meter face? I've seen a few equipment testers with a "?" between "Bad" and "Good". I have a battery tester with this, and tube testers like this are not uncommon. They are typically emission testers, which wire up the tube like a diode, with the grid wired to the cathode. As the tube ages, the cathode coating will wear out and emission will drop. The cathode coating wears out through normal use the same way an incandescent lamp wears out: at normal temperatures, it will evaporate and get deposited somewhere else in the tube. Emission testing is far from perfect, but it's a good first test to figure out e.g. which tube is a dud. I have a hard time caring because I never buy NOS tubes (same reason I don't buy CA3280s).

kw71 12y ago
A friend of mine has an emission tester (maybe it can put some signal on the grid - I haven't seen it in a while.) I've got a hickok machine that you look up the grid bias in the chart and can receive a reading in ... micromhos? Ok that implies conductance but that's a strange unit. I'm not sure these are "instruments." My treasure is a machine from soviet russia, it actually uses a signal generator to feed the grid, and measures transconductance in mA/V. It's got a bunch of power supplies, VTVM and microampere meter whose smallest scale resolves some nanoamperes, so I trust its methodology. It's nice to find the actual current passed by a rectifier tube instead of setting a meter bias knob to read out the 'strength' on a unitless 0-100 scale. But I never figured out how to intereperet the "?" on the emission testers. My tube fap shrine won't be complete until I get a Tek 575 though.
- dietrichepp 12y ago
  I'm not sure why the mho is a strange unit. It is just another name for the siemens (a.k.a. ampere per volt).