VHT Tube Tester 2 - Manual (Page 3)

PLATE DISSIPATION AND ADJUSTING THE BIAS
Fixed biased amps are typically biased below the maximum plate dissipation rating; typically
between 50% to 75% of the maximum plate dissipation.
Each tube will have its own inherent capabilities, the tube will show you when its maximum plate
dissipation has been exceeded — its plates will begin to glow orange/red (“red plating”). Itʼs wise
to heed the tubeʼs “red plating” warning sign; “red plating” quickly leads to tube failure and
destruction.
TYPICAL GUITAR AMP VOLTAGE AND CURRENT MEASUREMENTS AND
TUBE MANUAL MAXIMUM PLATE DISSIPATION RATINGS
EL84 = 12 watts
Plate voltage = 350 x 34 mA = 12 watts
6V6 = 14 watts Plate voltage = 400 x 35 mA = 14 watts
6L6GB = 19 watts Plate voltage = 450 x 42 mA = 19 watts
5881 = 23 watts Plate voltage = 450 x 51 mA = 23 watts
EL34 = 25 watts Plate voltage = 450 x 55 mA = 25 watts
6CA7 = 25 watts Plate voltage = 450 x 55 mA = 25 watts
KT66 = 25 watts Plate voltage = 450 x 55 mA = 25 watts
KT77 = 25 watts Plate voltage = 450 x 55 mA = 25 watts
6L6GC = 30 watts Plate voltage = 450 x 65 mA = 30 watts
7581 = 30 watts Plate voltage = 450 x 65 mA = 30 watts
KT88 = 35 watts Plate voltage = 450 x 78 mA = 35 watts
6550 = 35 watts Plate voltage = 450 x 78 mA = 35 watts
6550A = 42 watts Plate voltage = 450 x 93 mA = 42 watts
CALIBRATING THE METERS
While testing tubes in an amp, plug a high-quality DMM into the test pin jacks and compare the
DMMʼs readings with the meter readings; adjust the meterʼs calibrating screw to match the DMM
reading.
DYNAMIC TESTING
Plug an audio signal generator into your ampʼs input and observe the meterʼs response as the
signal level is increased.
Many smart phone signal generator apps are available; all you need is a stereo-to-mono cable to
connect your phone to your amp.
Do the meters “track” the same as the signal level is increased?
Uneven dynamic tracking can indicate output tubes that have poor dynamic matching, or perhaps
a poorly matched phase inverter/splitter tube, or perhaps other internal amp imbalances. A
certain imbalance can be considered musical to some ears; again, itʼs a matter of personal taste.
Guitar accents can produce very dynamic pulses, confirm the signal generatorʼs dynamic
response with guitar accents; punchy chords are a good way to observe the real-world dynamic
response.
Caution: Exceeding the meterʼs maximum level can damage the meters.
FEATURES AND SPECS
Includes two standard 8-pin octal-base adapters with dual banana plugs.
Adapters accept all popular octal-base output tube types:
6V6, 6L6, EL34, KT66, KT77, KT88, 6550, etc.
Two high-quality 3” diameter metal and glass analog milliamp meters (100 mA max).
Additional test-pin jacks for external digital multi-meter connection.
Durable vinyl-covered wood cabinet.
Requires no external power.
Dimensions: Height: 5.25” (133mm), Width: 8.75” (222mm), Depth: 2.5” (63mm)