20-05-2024, 01:35 PM
(This post was last modified: 20-05-2024, 01:35 PM by Mike Watterson.)
So the minimum to test valves is
1) The equipment the valve is used in
2) A DVM/DMM. The cheapest ones might have a 750V DC scale, but often flash over above 300V. They also often have only 1 M Ohm input on all voltage ranges. The 50V range on an old 20 K Ohm per volt analogue meter is as good and the higher ranges are better. Get two that do at worst 200uA DC current (so you can see 1 uA) and 20 M Ohm on voltage ranges.
3) A leakage tester. Not a Megger or Electrician's tester, but something limited to 200 uA on a short and at least 300V into 20 M Ohms. A flash from a single use camera works. Remove the xenon tube and the trigger button. Replace the 300V electrolytic with 1uF 400V and put at least 2 x 1M in series on the output. A series neon with a 200V 0.1 polyfoil cap across it will give visual indication.
Optional is a signal generator. It's handy if it has AM, but that can be added. It also needs an attenuator, which can be added, to give down to the level of a very weak station. The harmonics of a 30MHz max generator may work up to 90 MHz or 120 MHz for VHF. You don't need FM on a generator to test an FM tuner!
A 20 MHz scope is needed for TV and maybe taperecorders, but not for amps, recordplayers, radios or transmitters. A scope and maybe a spectrum analyser are needed for designing stuff.
Also optional, particularly for valve TVs, SMPSUs and series heater chain mains radios is a tungsten or halogen lamp in series. I've only ever needed it for one radio.
Obviously you need a separate 40W or more soldering iron, with 3mm flat or 3mm chisel tip and 60:40 solder. You might want separate lead free solder and iron for "modern" stuff. A spring loaded solder sucker for tags and fluxed copper braid for PCBs.
Don't plug in the equipment "just to see". The first thing is to check the valve on the output stage. There are parts to replace and things to check before powering on to check the output valve.
Next: Testing the output valve using the equipment instead of a valve tester.
1) The equipment the valve is used in
2) A DVM/DMM. The cheapest ones might have a 750V DC scale, but often flash over above 300V. They also often have only 1 M Ohm input on all voltage ranges. The 50V range on an old 20 K Ohm per volt analogue meter is as good and the higher ranges are better. Get two that do at worst 200uA DC current (so you can see 1 uA) and 20 M Ohm on voltage ranges.
3) A leakage tester. Not a Megger or Electrician's tester, but something limited to 200 uA on a short and at least 300V into 20 M Ohms. A flash from a single use camera works. Remove the xenon tube and the trigger button. Replace the 300V electrolytic with 1uF 400V and put at least 2 x 1M in series on the output. A series neon with a 200V 0.1 polyfoil cap across it will give visual indication.
Optional is a signal generator. It's handy if it has AM, but that can be added. It also needs an attenuator, which can be added, to give down to the level of a very weak station. The harmonics of a 30MHz max generator may work up to 90 MHz or 120 MHz for VHF. You don't need FM on a generator to test an FM tuner!
A 20 MHz scope is needed for TV and maybe taperecorders, but not for amps, recordplayers, radios or transmitters. A scope and maybe a spectrum analyser are needed for designing stuff.
Also optional, particularly for valve TVs, SMPSUs and series heater chain mains radios is a tungsten or halogen lamp in series. I've only ever needed it for one radio.
Obviously you need a separate 40W or more soldering iron, with 3mm flat or 3mm chisel tip and 60:40 solder. You might want separate lead free solder and iron for "modern" stuff. A spring loaded solder sucker for tags and fluxed copper braid for PCBs.
Don't plug in the equipment "just to see". The first thing is to check the valve on the output stage. There are parts to replace and things to check before powering on to check the output valve.
Next: Testing the output valve using the equipment instead of a valve tester.
