11-10-2016, 04:48 PM
(This post was last modified: 11-10-2016, 04:59 PM by Mike Watterson.)
You can't even compare most valve tester readings with volts and currents on DMMs
Almost all use AC or halfwave unsmoothed DC.
Most are very simple indeed, using a tapped transformers to adjust Vg1, Vg2 and Anode voltage. The current meter is calibrated. AC, halfwave, fullwave or DC is irrelevant to a TESTING direct filament valves, even 0.7V, 1.2V and 1.4V types. The reason you use DC on direct filaments is that otherwise you'd have hum. The original reason for DC on direct filaments was there was no AC! They then developed indirect filaments to have a cathode with no AC on it, it's much less efficient. The Series types needed more insulation so are less efficient and the radios take longer to warm up (almost a minute for some valve families).
Hickock and Taylor testers are very similar to that AVO you have.
Rolls Royce of Testers:
See http://www.radiomuseum.org/forum/tube_te...ciple.html
The Mullard High Speed Tester is designed for go/fail production, not really lab work or servicing. It's handy though for TV sets as they might have 20+ valves.
The very basic testers with only red/green fail/pass are less use today as they often don't have calibrated parameters to let you plot curves and are hard to use with out the table. The AVO VCM163 and related models let you test valves you don't have data for and plot the curves. As long as you can figure out the connections. Get the g1, heater (easy) and cathode right and the rest can usually be figured by trial and error.
My nearby friend has a simple Hickcock and the AVO VCM 163, I have a custom panel with the Ronald Decker uTester cpu board and serial connection to PC to trace curves. Like 163, I put loads of ferrite beads on every socket and looped to the start. I avoided expensive troublesome switches by a circle of 10 sockets and two in the middle (to TC outlets) and 2mm stackable patch cords to the test terminals.
If the tester has calibrated meters and a good range of Vg, Vg2 and Va then you can test ANY valve, it doesn't need a table.
If the tester is very basic and has no Vg2, then tie g2 it to Anode or add and extra switch to 50, 90, 120, 200 etc taps.
g3 to cathode.
If Hexode, Heptode, Octode etc then test the part used for oscillator first as a triode (one of the grids will be Anode), then tie all grids to 0V, or HT as required and vary RF in grid 0 to -15 and Anode as Anode.
Test Triode/Pentodes-Hexodes etc, triode first and then test mixer part as above
A "fail" valve but still 20% emission may still be perfectly usable. The "radio not working" is usually some other reason.
Almost all use AC or halfwave unsmoothed DC.
Most are very simple indeed, using a tapped transformers to adjust Vg1, Vg2 and Anode voltage. The current meter is calibrated. AC, halfwave, fullwave or DC is irrelevant to a TESTING direct filament valves, even 0.7V, 1.2V and 1.4V types. The reason you use DC on direct filaments is that otherwise you'd have hum. The original reason for DC on direct filaments was there was no AC! They then developed indirect filaments to have a cathode with no AC on it, it's much less efficient. The Series types needed more insulation so are less efficient and the radios take longer to warm up (almost a minute for some valve families).
Hickock and Taylor testers are very similar to that AVO you have.
Rolls Royce of Testers:
See http://www.radiomuseum.org/forum/tube_te...ciple.html
The Mullard High Speed Tester is designed for go/fail production, not really lab work or servicing. It's handy though for TV sets as they might have 20+ valves.
The very basic testers with only red/green fail/pass are less use today as they often don't have calibrated parameters to let you plot curves and are hard to use with out the table. The AVO VCM163 and related models let you test valves you don't have data for and plot the curves. As long as you can figure out the connections. Get the g1, heater (easy) and cathode right and the rest can usually be figured by trial and error.
My nearby friend has a simple Hickcock and the AVO VCM 163, I have a custom panel with the Ronald Decker uTester cpu board and serial connection to PC to trace curves. Like 163, I put loads of ferrite beads on every socket and looped to the start. I avoided expensive troublesome switches by a circle of 10 sockets and two in the middle (to TC outlets) and 2mm stackable patch cords to the test terminals.
If the tester has calibrated meters and a good range of Vg, Vg2 and Va then you can test ANY valve, it doesn't need a table.
If the tester is very basic and has no Vg2, then tie g2 it to Anode or add and extra switch to 50, 90, 120, 200 etc taps.
g3 to cathode.
If Hexode, Heptode, Octode etc then test the part used for oscillator first as a triode (one of the grids will be Anode), then tie all grids to 0V, or HT as required and vary RF in grid 0 to -15 and Anode as Anode.
Test Triode/Pentodes-Hexodes etc, triode first and then test mixer part as above
A "fail" valve but still 20% emission may still be perfectly usable. The "radio not working" is usually some other reason.
