The only WT110A
advertising I could find; not a lot of technical information, but
Here are the only
advertisements I could find for the RCA WT110A Automatic Tube
Tester. The advertisement top right comes courtesy of the
February, 1958 issue of Radio-Electronics, while the lower
center advertisement is from the August, 1959 issue of Electronic
Technician. The ads do not have a lot of technical information
explaining how it works, but then do we really need to know?
It does say enough to lure the prospective buyer over. What I like
about this tester is the following.
- The set up is 'automatic', including socket connections and all
- And, speaking of voltages, a 12VDC Plate supply is possible to
check the 'new' Automobile-Radio tubes.
- Rectifier tubes are tested at 140mA per plate.
- Leakage tests are done using either a high-sensitivity range or a
low-sensitivity range. Typical leakage tests, including those seen on B&K
tube testers, are limited to spotting about 1Meg leakage resistance.
- It tests 'twin tube balance', which is a fancy way of
saying you can test both halves of a 6SN7 or a 12AX7 without changing
switches or punch cards.
- The ad does mention that the pins are 'gold plated', and
this came in handy. When I bought my WT110A, it absolutely
needed a lot of TLC. The pins were still in great shape, and no
excessive cleaning under the panel was required. Bonus!
- Also mentioned in the ad is the thorough testing done; gas,
shorts, and the transconductance. This is all done with the simple
movement of the Telecaster-style selector switch. Very easy to
However, this tester isn't the perfect 'be-all-end-all' tube
tester. Remember; no tester is that good. What do I not
like about the RCA WT110A? A few things.
- The readings are not on a micromho scale, but an
arbitrary 'Replace - ? - Good' usually seen on emission testers.
This does not inspire confidence, despite the fact that this is a very
good tester. I suppose having micromho readings would necessitate
reading scales, and that would take away from the simplicity of just
inserting a card. It is still disheartening not to be able to 'see' how
matched the two sections of a 12AX7 are (or are not), and with a little
more accuracy than squinting over a 'Replace-?-Good' scale.
- Rather than having an AC fuse, RCA uses a 56-ohm
resistor. It is difficult to locate, and is not mentioned in the
owner's manual (you need to be able to interpret the schematic)! Not as
user-friendly as having a panel-mounted bulb (like Hickok), or
even a 'regular' fuse.
- The switching is very strange. The switch used is a
three-position 'center-off' switch. That's only half of the story; the
center position is the 'Test' position! It is always good practice to
do 'Shorts' tests before testing any tube; if the tube fails the
'Shorts' test, no further testing is advised. However, it is possible
to have the 'SELECTOR' control to 'QUALITY' by an oversight, and have a
shorted tube 'pin' the meter movement. You are supposed to hold
the 'CALIBRATE/TEST' switch in the 'calibrate' mode (which is just a
'Line Adjust' setting) and set the meter movement to show
'center-scale' while the tube is warming up. I damn near wrecked the
meter movement once, and I believe this is how that almost
happened. While the tube was warming up (it was not shorted at
all), the meter was measuring full B+ until the tube 'settled down',
and a voltage drop was developed across a plate load. As I watched the
needle try to jump right out of the meter housing, I cursed RCA,
and all of their heirs.
I still really like the RCA WT110A; it is a very good
tester. If you buy one, please make sure you have the owner's manual.
The calibration is very difficult at the best of times, and without
the manual it is useless to even try and 'wing it'. And an
'uncalibrated' tube tester is just as useless.
THE IDIOT'S GUIDE TO TUBE TESTERS