MIL-DTL-25576E
APPENDIX A
ALCOR MARK 8A TUBE DEPOSIT RATER MODIFICATIONS
A.1 Scope. This appendix gives instructions for the modification of Alcor Mark 8A Tube Deposit Rater
(TDR) so that accurate measurements of the Delta Spun TDR ratings can be obtained. This appendix is
a mandatory part of the specification. The information contained herein is intended for compliance.
A.2 Summary. JFTOT heater tubes often have a pretest Spun TDR rating of zero or below when rated
with the Mark 8A TDR IAW ASTM D 3241. This occurs because the surface finish of the heater tube test
section is difficult to control and new heater tubes have pretest ratings which range from about -5 TDR
units to about +5 TDR units. To compensate accurately for differences in the pretest ratings of the
JFTOT heater tubes, the pretest rating is subtracted from the post test rating to obtain the Delta Spun
TDR rating. However, the production model of the Mark 8A TDR cannot rate tubes below the zero TDR
level since the range of the meter is 0 to +50 TDR units. Accurate positive and negative TDR values can
be obtained when the original meter is replaced with a digital millivolt meter that can read both positive
and negative voltages. (NOTE: If the modification instructions given below are followed, 1 millivolt (mv)
will equal 1 TDR unit.) This appendix gives the instructions necessary to make this change.
A.3 APPARATUS
A.3.1 Tube Deposit Rater (TDR). Alcor Mark 8A Tube Deposit Rater IAW ASTM D 3241.
A.3.2 Digital meter. Digital millivolt meter with a minimum scale range of ±50 mv and a minimum
accuracy of ±2 percent at 50 mv. The digital millivolt meter must have a range of ±199.9 mv and input
power requirements of 120/240 VAC, 50 to 400 Hz.
A.3.3 Resistor. A 1000 ohm resistor, ¼ watt (required for Option 2, below).
A.3.4 Hardware. Suitable electrical wiring, connectors, and other hardware to connect
electrically the digital millivolt meter to the Mark 8A TDR and, if desired, to physically attach the digital
millivolt meter to the Mark 8A TDR.
A.4 PROCEDURE
A.4.1 Option 1. Leave the existing meter in place. This option will enable the use of the TDR
with either the existing meter or with the digital millivolt meter, but not concurrently. The two meters will
not give identical readings; therefore, the TDR must be calibrated using the meter selected for use.
A.4.1.1 Hook-up. Connect the digital millivolt meter in parallel with the existing meter. It may be
necessary to drill holes in the TDR case to bring out electrical leads from the existing meter terminals to
the digital millivolt meter. The 1000 ohm resistor is not used with this option. To avoid confusion, it is
suggested that the face of the existing meter be covered when the digital millivolt meter is used.
A.4.2 Option 2. Replace the existing meter. This option is recommended, as there will be a
small but significant difference in the readings of the digital millivolt meter and the existing meter when
option 1 is used. Confusion could arise with both meters operational.
A.4.2.1 Hook-up. Remove the existing meter from the Mark 8A TDR. Connect the 1000 ohm
resistor between the two leads that were connected to the existing meter. Connect the digital millivolt
meter in parallel with the 1000 ohm resistor. With the existing meter removed, leads from the TDR to the
digital millivolt meter can be brought out through the front of the TDR, as there will be a 2-inch diameter
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