AVO 160A, Operating Instructions And Maintenance Manual

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This document is a collaboration between Martin forsberg, Sweden, and Euan MacKenzie, Australia. Copyright Martin Forsberg &
Euan MacKenzie 2010-11-18
AVO CT160A Operating Instructions and Service Manual
This AVO CT160A manual is the result of combining (and editing) two different sets of photocopies of
AVO CT160A manuals and also from information from the original AVO CT160 manuals. This AVO
CT160A manual has been kept as original as possible, even though some photocopies of the AVO
CT160A pages have been replaced with AVO CT160 pages where the text did not differ in any point, but
where the quality of the CT160 scanned pages was much better than the CT160A scanned pages. All
figures and photos have been kept in their original shape although most have had to be edited due to the
poor quality of the original photocopies.
The schematics at the end of the manual have been extended with three new sets where the first is an
unaltered original redrawn schematic, the second schematic is a redrawn and corrected schematic and
the third is a redrawn, corrected and modified schematic. The second schematic has been corrected in
the following areas:
D2: Changed from 66V RMS winding to 99V RMS winding, calculating the current in the circuit
shows that the 99V RMS winding is necessary for the circuit to work correctly.
R4 & R41: Changed places in schematic, the component list on page 17 of the Service Manual
and also the component list on the page before the original schematic shows this as the correct
order, as well as an internal component placement comparison between a CT160A and a CT160.
R37 & R37 shown as R37A and R37B as per component list on page 18 of the Service Manual,
consisting of one 13
Ω
"selected" resistor each.
SH6: Ground connection for tags 2-5, was missing from original CT160A schematic but can be
found in later CT160 schematics and also in the original CT160A & CT160 testers.
WIRES & COMPONENTS: Moved for clarity.
The third schematic has been modified in the following areas:
All of the corrections above from the second schematic plus:-
D5, R42 & R38: Anode voltage rectification added, components used D5 = D1, R42 = R38 = 100
k
Ω
± 10% 1 W – this modification has been tested and proved to work in an original AVO CT160
and is also used by AVO in the AVO Mk IV.
D6, D7 & C4: Meter protection circuit added, D6 = D7 = D1, C4 = 8µF / 63VDC Non polarized
(preferably Polypropylene) – this modification has been tested and proved to work in an original
AVO CT160 and is also used by AVO in the AVO Mk IV.
If you want to read more about the inner workings of the AVO Valve Testers including the AVO CT160
and AVO CT160A I recommend that you visit the “
UK Vintage Radio Repair and Restoration
Discussion Forum
“
here
http://www.vintage-radio.net/forum/index.php and read the threads:
“Everything you wanted to know about the inner workings of an AVO Mk IV Valve tester!”
“Some more that you wanted to know about the inner workings of an AVO Valve tester!”
“All that you wanted to know about the inner workings of an AVO CT160 Valve tester!”
“AVO CT160 - anode current measurements, calibration resistors and the meter workings!”
“AVO CT160A – Special edition of the AVO CT160 - comparison!”
I have included adapted versions of the CT160A and CT160 texts above in this document.
The work of editing and testing the corrections and modifications in the AVO CT160A manual, and writing
of the articles above, has been performed by Martin Forsberg, Sweden, and Euan MacKenzie, Australia.
Sweden 2010-11-18