VHT TUBE TESTER 2
MONITOR YOUR OUTPUT TUBE PERFORMANCE
The VHT Tube Tester 2 provides two completely independent current-measuring tube tester sections. Simply plug your tubes into the adapters and then plug the included 8-pin octal-based adapters into your amp.
The two high-quality analogʼs cathodemilliampcurrentmeters.Youmeasurecan usethe tube
these meaʼsurementsreal to observe your tube -time dynamicʼre performance, see how well they matched, adjust the bias, monitorʼs perfyormanceurtube as they age, check for unstable
conditions, and more.
Additional test-pin jacks are provided for precise digital multi-meter measurements and analog meter calibration.
The VHT Tube Tester 2 is an affordable bench and road tool that lets you see how your output tubes are performingʼs time inreplacereal timente,andor awhetherbias adjustment,it etc.
Get the most from you tubes — and amplifier — with a VHT Tube Tester 2.
SET UP
Setup is easy, simply unplug your output tubes andʼscarefully plug them into the Tube Tester 2 adapters, then plug the adapters into your tube sockets.
Pay cloʼsealigniattentiongguideto thepin,tubeand be sure the adapters are aligned correctly
with your tube sockets. (An incorrectly installed tube or adapter can cause serious damage to your amp and/or tubes.)
Some tubes may be a tight fit in the adapter. Tube pin diameter varies slightly between different tube manufacturers, and sometimes there will be some excess solder on the pin. For an easier fit, you can file-down excess solder with an ordinary fingernail file.
After the tubes andʼsadbananapters plugshave beento properly secured, connect the adapter the meter unit.
Test-pin jacks: For precise digital measurements and analog meter calibration, plug a DMM (digital multimeter) into the front panel test-pin jacks and set the DMM to its millivolt range; the test-pin jacks measure the voltage drop across a 1-ohm precision cathode resistor, 1 millivolt = 1 milliamp cathode current.
You canʼs alsobananaplugjacksthe adapterdirectly into a DMM (set for milliamps).
OPERATION
While other tube testers test your tubes externally, the truest and most relevant test is how your tubes perform in your amplifier.
The ʼTubeshighTester 2 -quality analog metersʼ provide a unique window into your tube performance. Analogʼs meters provide a much better view of your tube dynamic response than digital meters (which are still useful for precise measurement of stable idle currents and voltages, and also for meter calibration).
After the tubes and adapters have been installed properly, power-up the amp as usual.
OPERATION, CONTINUED
Observe the meters as the tubes warm up and slowly begin to draw current.
The meters will show a gradual rise in current until the tube idle current begins to stabilize. (If the meters deflectʼs polarityin the.)negative direction, reverse the banana plug
If one of the tubes, or both, continue to draw current without stabilizing, this is a clue that the tube is defective (prone to “runaway”); it needs to be replaced.
Do the two tubes rise at about the same rate, or does one tube rise faster than the other?
Tubes with similar characteristics will warm-up at similar rates. An unusually fast warm-up rate can indicate a problem; it could be a tube problem or perhaps an amp problem.
When the idle current stabilizes, how closely are they matched?
The analog meters show 4 milliamps per division; a close/acceptable match is generally considered to be something less than a 10% difference between the two tubes.
With practice, you will learn to quickly recognize common tube problems such as runaway “red plating” as well as unstable conditions that cause unreliable operation.
MICROPHONICS TEST
Tap the tubes and listen for microphonic rattles and rings while also watching the meter for unstableʼ rubberreadingsknee.(Areflexdoctorhammer can be purchased cheaply on eBay, or
a pencil with added eraser is also good, and a good alternative to the old-fashioned tried-and-true “fingernail flick.”) Unstable meter readings indicate a tube with loose internal components; these tubes should be discarded.
BIASING
Afterʼve cyonfirmedu that your tubes are stable and the idle current is reasonably matched, you
can use the Tube Tester 2 to adjust the idle current level (assuming your amp has an adjustable “fixed-bias” type circuit).
Simply put, “proper biasing” is any bias setting that sounds good to you without destroying the tubes. It is, after all, about tone, and tone is of course very subjective. Some people prefer a hot bias (high current), while some people prefer a colder bias (lower current). Fine-tune by ear, and
season to taste,ʼ practicalwhile alwayslimits (itsbeingrealaware of the tube |
-life maximum plate |
dissipation). |
|
An output tube has a maximum plate dissipation rating; these generalized ratings were developed many decades ago, and they can be found in old tube manuals and reproduced online.
But tube manufacturing is different now; some currently manufactured tubes can easily exceed the old maxiʼt measureumratings,up. Sowhileth othersldmaximumdon plate dissipation
ratings should be regarded as good guidelines rather than absolute limits. Your results may vary.
CALULATING PLATE DISSIPATION
To accurately calculate aʼstubeplate dissipation,ʼ plate voltageyou need.Thisto know the tube is the voltageʼs platebetweenand its cathodethe tube(pin 3 and pin 8). You can measure this with aʼll DMM,needtobutremoveʼsyousocketthe. chassis to access the tube
If this is not convenient, you can estimate; most amps with large octal (8-pin base) tubes (like 6L6 or EL34, for example) operate at around 400 to 475 volts on the plate, while smaller tubes like EL84s and 6V6 tubes will typically operate at lower plate voltages, around 350 volts or less if thʼreycathode biased.
PLATE DISSIPATION FORMULA
Plate voltage x current = plate dissipation (watts)
Example: 450 volts plate voltage x 40 mA (meter reading) = 18 watts plate dissipation; this would be considered safe for an EL34 but dangerous for a 6V6.
Some cathode biased amps are known to routinely exceed the recommended maximum plate dissipation,ʼ be surprisedso donif your meter readings indicate plate dissipation approaching or
exceeding the textbook maximum rating.
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