tube-tester (Tweaks)

by madprofessor , 27777 Ganderkesee, Germany, Monday, April 13, 2009, 17:39 (5485 days ago)

I was simply fed up by the accuracy standard tube-testers deliver. So I got the idea to build something better:
For a start, I took a Neuberger 370 tube tester ( Build 1951 !). This tester has the advantage, that it is an excellent switch-matrix with access to all voltages. Also very easy operation. The disadvantage is the unstability of the build in power supplies, the unaccuracy of the http://forum.bd-design.nl/images/uploaded/2009041317212449e3587411274.jpg meters and it can not be remote controlled by a computer.
So I used the Neuberger 370 only as a switch matrix ( The unit on top of the rack) For meters I used two HP 34401A 6 1/2 digits mulimeters and a HP 34970A scanner with build in 6 digits multimeter. That unit has an input card with 20 inputs, which can be switched to the desired points of interest.
For grid voltage I use a very accurate Rohde & Schwarz NGPS dual voltage source.
For anode voltage I use a Rohde & Schwarz NGP 300/06 Powersupply.
For heater I use a HP 6632B Powersupply.
All units have also rear connectors, so wiring can be put inside the rack. All units can be controlled by IEEE ports by Computer.
That way selecting especially dual triodes is really a pleasure.
The system- accuracy is better than 0,01%.
Also having acces to all voltages, it´s easy, to input also ac-voltage from one of my sources and mesure the results with an analyzer (I use the Rohde & Schwarz UPD in that case). By removeable shorting plugs in the Neuberger 370 the necessary connections can be easyly done.
Matching the input tubes of an SET amplifier exactly gave of course some sonic improvements.
In comparison, the original Neuberger 370 was including drift and other hassles no more accurate than 10 % - complete system..
In case the anode-power supply has no high enough voltage, I´ve higher capacity psu´s which can be connected by jumper wires and adaptors ( for the GM 70, 845, etc).
A tester like that described, makes work much easier, especially tube matching - in the end I got an excel- list, with the matching tubes highlighted.
Best regards
Stephan