AVO CT-160 --- Help

[webercarbmann]

Hi there - I have a problem


I was just testing some EL34 when the meter stoped working

What am I going to do now. Does anny of you know where to get a "New" meter or where to get the old meter repaired?

Is there annything I can do myself to fix it again?

Thanks Peter Jensen

[fdegrove]

Hi,

Is there annything I can do myself to fix it again?

Quite possibly...
Have you already opened it/or looked for and checked for a popped fuse?

Have you tried it with a lower power valve? ECC83, EL84, something along those lines...

If the fuse(s) check out O.K. and the smaller valves aere fine it could be a faulty contact in the octal socket.

I'm not sure about the AVOs but alot of these meters used a rheostat to set/correct the line voltage. Maybe you incidentally turned it down too much.

Could be a dead rectifier valve inside as well....could be a number of things really but this is often stuff that just works and works, for ages.

Cheers,

[webercarbmann]

Hi again

Thanks for replying.

The valve tester is still working. The tube in the tester keept running. I am Quite syre that it is only the meter that is not working.


Peter

[analog_sa]

I have a service manual for the 160 which i once used to own. Send me an email if you want it. You should really open it up and test the moving coil system before jumping to conclusions. If a coil is really burnt you only stand a chance if the open circuit point is visible and accessible.

[316a]

Originally posted by webercarbmann
Hi again

Thanks for replying.

The valve tester is still working. The tube in the tester keept running. I am Quite syre that it is only the meter that is not working.


Peter

Hello ,
With the tester set to 'C/H' , does your valve under test light up ?Can you obtain a reading when set to mains calibration ? You should be able to obtain FSD on the meter . Inside the tester there is a pot which is the only adjustment , if you can't adjust FSD when calibrating the mains you will need to adjust this . If there is a red light on behind the meter scale , open the tester and reset the trip relay . If you can't get any meter movement , open the tester , check the fuses . Across the meter is a shunt resistor , desolder this and measure for continuity . If this is open , your meter is stuffed . If the meter obtains a measurement , solder the shunt back in and start to fault find .
The circuitry is very simple , there is only a single 6AL5 inside (I can send you one if you wish) , the grid pot can be a problem and is unreplaceable , also the thumbwheel switches may need a clean . Gerry at Crowthorne Tubes is the guru on these things . He can supply circuit diagrams and also has a replacement meter movement . Hope this helps

cheers

316a

[webercarbmann]

Hi again

Thanks a lot for the advide. I will open it up and check the things mentioned. It is nice to nav that a replacement meter it posible get get. About the grid pot - it sucks. I constantley have to ajust it to keep the negative grid voltage konstant. I always use a digital multimeter to check the actual voltage when testing.

I will let you know how the repair is comming up


Peter Jensen, Denamrk

[webercarbmann]

Hi again

Thanks a lot for the advice. I will open it up and check the things mentioned. It is nice to know that a replacement meter it posible get get. About the grid pot - it sucks. I constantley have to ajust it to keep the negative grid voltage konstant. I always use a digital multimeter to check the actual voltage when testing.

I will let you know how the repair is comming up


Peter Jensen, Denamrk

[316a]

Originally posted by webercarbmann
Hi again

Thanks a lot for the advice. I will open it up and check the things mentioned. It is nice to know that a replacement meter it posible get get. About the grid pot - it sucks. I constantley have to ajust it to keep the negative grid voltage konstant. I always use a digital multimeter to check the actual voltage when testing.

I will let you know how the repair is comming up


Peter Jensen, Denamrk

Hello ,
Good idea , I do this also . The grid pot in mine has been changed . The pot that should be fitted is a weird log/lin/log but mine is a linear so I can't use the dial . Remember to remove the meter when taking cathode leakage tests , that is if you get the thing working . Wish you the best of luck with your faultfinding

cheers

316a

[webercarbmann]

Hi again

Now I have tryed several things. Both the 2A fuses are ok. The meter powers up/read light in the bulb between the fuses. Are there anny fuses inside the meter? I tryed to lift the 10K resistor over the meter and mesure the resistance over the meter. It was 1.4 Mega Ohm. - So it is now open. The manual says somthing about setting the selector to 0 0 0 0 0 0 0 0 0. I tryed that also. Still no result. Anny ideas please??


Peter

[webercarbmann]

Hi again

When messuring across the meter at start ud, the voltage changes from 0 VCD to 340 mVDC in about 30 Sec. this relates to the movement of the neadle at startup. This must mean that the meater unit is defective. Where can I by a new meter?


Peter