Valve testing

Most of the valve testing that I do is as a routine part of the service and repair of valve amps. I don’t charge for the testing of valves as a part of a repair and valve testing is included in every valve amp service. However I’m approached from time to time by people who just want valves testing either to sell or for peace of mind. For this, I charge £3/valve, with a minimum of 3 valves. For quantity valve testing requirements I’m happy to negotiate a reduced rate.

If you’re bringing me a repair and you have a couple of old valves you’d like me to test then no worries, that’s FOC and I can use them for the repair if they’re still good. If you’ve got a whole box, I may charge though!

Digital Valve testing

VT1000 Valve testingI do most of my valve testing with an Orange VT1000 valve tester. There are more advanced valve testers around, and I’ve used traditional units by Avo in the past but this does exactly what I need at Ampworks. It tells me if the valve works and whether it’s suitable for the customer’s amp. This is a digitally controlled basic valve tester that gives a pass/worn/fail result as well as a matching value to allow the grouping of power valves into matched pairs or matched quads (or matched duodecads like this mesa boogie bass 400+ repair!). If you’re testing a dual triode then it gives a matching value for each triode, allowing you to determine if a valve is suitable for phase inverter duties.

The valve tester tests the following valve types:

Octal power valve testing (pentodes and tetrodes):

  • EL34/6CA7;
  • EL34L;
  • 6L6;
  • 6V6/6v6GTA;
  • KT66;
  • KT77;
  • KT88;
  • 6550;
  • 5881;

Noval power valve testing (pentodes):

  • EL84/6BQ5;

Noval preamp valve testing (dual triode):

  • ECC81/12AT7;
  • ECC82/12AU7;
  • ECC83/12AX7;
  • ECC99;
  • 12BH7

Upon which it performs the following valve tests:

Valve tests:

  • Heater filament test: Short circuit
  • Heater filament test: Open circuit
  • Heater filament test: Tolerance check
  • Heater cathode insulation: Leakage
  • Heater cathode insulation: Short Circuit
  • Tests for heater current abnormalities
  • Amplification factor
  • Voltage gain
  • Power gain
  • Screen grid test
  • Mutual conductance test
  • Dual test for double triodes
  • Emission
  • Inter electrode leakage
  • Inter electrode short circuit
  • Flash-over (arc detection, high voltage breakdown)
  • Gas ionisation test

Other ‘basic’ valve testing

The above tester does nearly all the valves that are commonly available on valve amps from the late 1950s onwards. I also do a ‘basic’ test that checks basic function but cannot guarantee valve performance.

  • Heater test: Apply the rated heater voltage to the filaments, check the current draw and ensure filaments are glowing.
  • LV DC short test: Multimeter test to ensure that no pins (except filaments) measure a low resistance at DC. Low voltage, does not run the valves at rated anode voltages.

I’ve done these basic tests on:

MKT4/7 ( 7 pin Beam Tetrode) Sensibly equivalent¶ to:- 7A2 – AC/Pen – APP4A – CV1683 – MP/Pen – KT42 – Pen4VA – A70B – N40 – P4VA
B65 (Dual Triode) Sensibly equivalent to:- 13D2 – 6SN7GT – CV1988 – ECC32
B36 (Dual Triode) Sensibly equivalent to:- 12SN7GT – CV925
DL63 (Dual Triode) Sensibly equivalent to:- CV2912 – DH147 – 6R7G – OM4
GZ32 (Rectifier) Sensibly equivalent to:- 5AQ4 – CV593 – 52KU – 5V4G – 5Z4G
U18/20 (Rectifier) Sensibly equivalent to:- 45IU – AU1 – CV1264 – FW4-500 – NU12 – FW4-800 – CV31 – 4/100BU – RV200/600
U50 (Rectifier) Sensibly equivalent to:- 5Y3G – CV1268 – CV3754 – 5Y3G/GT
L63 (Triode) Sensibly equivalent to:- 6C5 – 6J5G – CV1067 – CV1932 – VR67 – VT154
H63 (Triode) Sensibly equivalent to:- 6F5G – CV1073 – VT73