Zeners and voltage regulation

[M Gregg]

The tube would not draw to much current if it was "bad" unless short circuit so forget the tube 12AT7.

Check the voltage on pin 3 it should be regulated with the zener. Compare with other channel.

I hope you are familiar with HV working?

You can just check across the zener (DC volts).. remember not to run the amps with no load... If the drawing is correct it should be the cathode.



Regards
M. Gregg

 

[WILD1]

Hi DF96,
Grid voltage on that side of the tube is 8.4 volts I believe And the voltage at the cathode is 8 volts I believe. I checked that two days ago. I could check it again. I could also check the other amp for a comparison.

 

[WILD1]

Hi greg
That is the cathode. Like I said I checked it several days ago and didn't really compare them to the good amp.

 

[M Gregg]

So pin 3 is 8 volts on both channels?

You must compare..


Regards
M. Gregg

 

[WILD1]

Hi greg
By the other channel I take it you mean the other side of the tube. Voltage at the cathode pin # 8 is 12,2 volts. Pretty much right

 

[M Gregg]

There also seems to be some form of crowbar protection.

We need to find out if its V13 or the protection.


Regards
M. Gregg

 

[M Gregg]

Hi greg
By the other channel I take it you mean the other side of the tube. Voltage at the cathode pin # 8 is 12,2 volts. Pretty much right

Compare all voltages to the same point on the good amp..

 

[WILD1]

Is that what you needed Greg or are you talking about a comarison between pin 3 in the sick amp and the good amp

 

[M Gregg]

Q2 should have -25 V on the base. If the drawing is correct



Regards
M. Gregg

 

[M Gregg]

Is that what you needed Greg or are you talking about a comarison between pin 3 in the sick amp and the good amp

Yes..

 

[WILD1]

Okay I will get you those figures Greg. Boy you people are running me ragged. One minute I can't get an answer the next I can't keep up. I' a bovine herder not a typist. I do greatly appreciate it.

 

[M Gregg]

Just for info...Stay with the tube at the moment..

Q4 is the crowbar protection.

Do not disconnect it..Untill we know more..

Regards
M. Gregg

 

[M Gregg]

Okay I will get you those figures Greg. Boy you people are running me ragged. One minute I can't get an answer the next I can't keep up. I' a bovine herder not a typist. I do greatly appreciate it.

We can't go further untill you get the values on the tube. It may be that the crowbar is in operation.

This would mean out of spec voltage... so i'll catch you laters when you get the values.


Regards
M. Gregg

 

[WILD1]

Okay Greg, this is values for the good amp. Pin1 [anode] 300.4 volts pin 2 [grid] 7 volts pin 3 [cathode] 11.5 volts pin 8 [cathode] 11.7 volts

 

[M Gregg]

11.7 on pin 3?

This is 8~ on the bad amp?

What was pin 1 value on the bad amp?


Regards
M. Gregg

 

[WILD1]

Yes pin 3 0n the sick amp is 8 and pin 1on the sick amp is264 volts. I could check it again .

 

[evette]

Check that the 2n4403 is turning on the scr or is it just triggering incorrectly,, Evette

 

[M Gregg]

If the scr crowbar is on you will have no or low voltage.

Check the voltages around Q2 compared to the drawing and also the good amp..List what you get for the good amp and the bad amp in the same post..

As evette has said.
You have to be carful the crowbar is their for a reason if you stop it working to see whats wrong then you may damage something..

Regards
M. Gregg

 

[M Gregg]

Something else you could check,

R144 has a value of -253V check with both amps what you have?


Regards
M. Gregg

 

[kevinkr]

Check ALL op-amps - this is usually what blows up in the regulator circuits of these amps. Don't ask me how I know this.. 😀