I have an AVO 2 panel valve tester which I intend to clean and get working.

I have the circuit diagram and operating instructions. The Serial No. is
12372-147.



As I don't know if it is faulty or not I am proceding with caution.

At present I am checking the 'Meter unit' for correct operation before
plugging in the 'socket panel' as I don't want to damage the sensitive
moving coil meter movement.



The voltage outputs on the 9 pin socket on the side of the Meter box seem OK
(i.e. Anode, screen and heater)



I assumed that I could plug a 100kOhm resistor between the Cathode socket
(No.6) and a LT- heater socket (No.4) of the 9 pin socket and then push the
toggle switch sideways to check 'C INS' (cathode insulation).

However the meter needle does not move. If I turn the 'Set Zero' knob
anti-clockwise the needle vibrates and moves to the left.



I have cleaned and tested the contacts on the toggle switch. I have
soldered an IN4006 diode in series with the metal rectifier in case it was
faulty.

35 volts AC can be measured across the test resistor.



Am I wrong to expect the tester to measure this 'simulated faulty cathode
insulation'?



Furthermore, should I replace the 0.05microFarad paper capacitor with a
polypropylene version to improve reliability?



Any other tips would be greatly appreciated.



Regards,

Rudge

Rudge wrote in message
...
I have an AVO 2 panel valve tester which I intend to clean and get
working.

I have the circuit diagram and operating instructions. The Serial No. is
12372-147.



As I don't know if it is faulty or not I am proceding with caution.

At present I am checking the 'Meter unit' for correct operation before
plugging in the 'socket panel' as I don't want to damage the sensitive
moving coil meter movement.



The voltage outputs on the 9 pin socket on the side of the Meter box seem
OK
(i.e. Anode, screen and heater)



I assumed that I could plug a 100kOhm resistor between the Cathode socket
(No.6) and a LT- heater socket (No.4) of the 9 pin socket and then push
the
toggle switch sideways to check 'C INS' (cathode insulation).

However the meter needle does not move. If I turn the 'Set Zero' knob
anti-clockwise the needle vibrates and moves to the left.



I have cleaned and tested the contacts on the toggle switch. I have
soldered an IN4006 diode in series with the metal rectifier in case it was
faulty.

35 volts AC can be measured across the test resistor.



Am I wrong to expect the tester to measure this 'simulated faulty cathode
insulation'?



Furthermore, should I replace the 0.05microFarad paper capacitor with a
polypropylene version to improve reliability?



Any other tips would be greatly appreciated.



Regards,

Rudge




Is that Avo and then "2 panel" as it has one panel of meter + controls and
one panel with valve bases? or "Avo 2" as a model number?

The basic filament check function is OK I take it.
I use an Avo 160 and would suggest that if its got an electromechanical
meter cut-out it would be advisable to confirm that the trip mechanism and
overall function is in good working order.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On Oct 28, 8:51 pm, "Rudge" wrote:
I have an AVO 2 panel valve tester which I intend to clean and get working.

I have cleaned and tested the contacts on the toggle switch. I have
soldered an IN4006 diode in series with the metal rectifier in case it was
faulty.

Furthermore, should I replace the 0.05microFarad paper capacitor with a
polypropylene version to improve reliability?

Any other tips would be greatly appreciated.

Rudge:

I have seen only two AVO testers in the flesh, so the tips I give you
will be generic, and not specific to that tester.

a) Having the schematic is important and helpful.
b) REMOVE the questionable diodes and REPLACE them. If you must leave
them in place for originality and/or authenticity, then disconnect and
secure one end of the diode(s) and leave only the working
replacement(s) only in the circuit.
c) 1N4007 would be my suggestion as a general replacement rectifier
diode. A bit of overkill, perhaps but no more expensive than the
1N4006.
d) Yes, replace the cap. Equal capacity, equal-or-greater operating
voltage.
e) Clean the switches, pots and sockets (see more below) carefully.
For switches, a lubricating cleaner is worthwhile. For plugs use only
100% volatile cleaners and _NEVER_ clean the socket itself, especially
if it uses phenolic wafers anywhere. Cleaning sockets with solvents
can drive metallic particles everywhere the fluid goes and leave them
behind to form carbon tracks, annoying shorts and so forth. If you
must clean a socket, use a wooden toothpick or fat needle. Nothing
that may cut or abrade the contacts.

AVOs are nice testers. The closest US equivalent would be the upper-
end Hickoks.

Peter Wieck
Wyncote, PA