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-   -   AVO CT 160 Regulated Grid Voltage Supply (https://www.vintage-radio.net/forum/showthread.php?t=161354)

Karsten 12th Nov 2019 8:25 pm

AVO CT 160 Regulated Grid Voltage Supply
 
2 Attachment(s)
I have designed a fairly simple and well functioning regulator circuit for the grid voltage. Details attached.

Dekatron 12th Nov 2019 9:13 pm

Re: AVO CT 160 Regulated Grid Voltage Supply
 
Is the CT160 still accurate on all other tests like GAS, Heater continuity and isolation measurements and the calibration setting?

Does the circuit affect the tester in any way on the frequency span that it is supposed to work at, 50-500Hz?

Karsten 12th Nov 2019 9:43 pm

Re: AVO CT 160 Regulated Grid Voltage Supply
 
HCONT, A/R, S/R, CH/R, C/H tests remain unaffected as they are independent of the grid voltage circuit.
SET~ had been modified before: voltage between the 99 V and 137.5 V taps is measured, similar to CT160A.
I have no means to run the tester with 500 Hz but I cannot see any functional obstacles. The regulator circuit "should work" as well. BTW, who will use the instrument nowadays on mains frequencies other than 50/60 Hz?

Dekatron 12th Nov 2019 10:08 pm

Re: AVO CT 160 Regulated Grid Voltage Supply
 
Good to know that no other tests are affected.

Also good to know that the SET~ circuit had been modified as that was my main concern when it comes to this regulator modification - that circuit relies on the two different AC voltage levels for the mean value of them to get the other measurements correct in the normal CT160 but only on one voltage in the CT160A.

Since the mains voltage can hardly be said to be 50Hz or 60Hz nowadays as it is sometimes not regulated well, as well as it is full with other frequencies overlaid on it for communication purposes of for instance electricity billing meters, I think that your circuit will work well on other frequencies as long as there is no bandwidth limit.

How well does the regulator withstand a short from the anode, or any other electrode, into the grid electrode (or short to ground)?

I guess that not many people run it on anything else than 50Hz or 60Hz except me when I ran some tests with the help of some military dynamotors (motor/generators) that could be used at 50Hz, 60Hz and 440Hz.

I wanted to check the difference between the voltages and frequencies as AVO stated that some small difference could be seen as well as the compensating capacitors being there for that reason. I also wanted to check what the difference was between the not so nice sinusoidal voltage from the mains outlet compared to a pure sinusoidal voltage from the dynamotor. Everything looked much nicer on the scope with a pure sinusoidal voltage compared to the regular mains voltage but the measurements wasn't affected much as long as the tester was properly calibrated, well within what AVO said it would work as.

/Martin

Karsten 13th Nov 2019 12:13 am

Re: AVO CT 160 Regulated Grid Voltage Supply
 
One of the front panel fuses has been rewired in line with the grid potentiometer wiper and fitted with a 32 mA fast blow fuse. This fuse should blow in case of a faulty valve or erroneous roller switch setting. The BC238 transistor is plugged into a short socket strip, not soldered even though the transistor cannot be destroyed by a short in the grid volts network because the 47 K base resistor limits the collector current (beta ~300).

Dekatron 13th Nov 2019 9:27 am

Re: AVO CT 160 Regulated Grid Voltage Supply
 
Ok, if you could make a completecdiagram with all dependencies and modifications to get this regulator to work properly and publish here would help a lot.

/Martin

Karsten 15th Nov 2019 3:55 pm

Re: AVO CT 160 Regulated Grid Voltage Supply
 
1 Attachment(s)
Attached I have compiled the relevant earlier modifications of my VCM https://www.vintage-radio.net/forum/...ad.php?t=85697 together with the more recent ones.


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