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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Zeners and voltage regulation

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#61
Thanks for the input Wavebourn. I checked that tube out. #3 is the anode or plate and is getting somewhere around 650-655volts. It should be around 630 volts but my source at my house is 122 volts and I was thinking that might be why.#8 is the cathode and it is at 299volts it should be 330 volts. I felt that low voltage at the control grid #5 260volts where it should be around 320 volts might be the reason for the low voltage at the cathode. This control grid is associated with this circuit we have been discussing. Thanks again

WILD1
 
#62
There is Seven 1N4756s and they are 47 volts there is one 1N4759 and it is 24 volts That is 353 Volts, However the more recent schematic that I have says 320 volts up by the anode of V13. Thanks for the input.

WILD1
 
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#63
OK sometimes,

Its interesting to change direction and reassess so what voltages do you have on the supply rails. The drawing says 433V 330V 318V at the top.

So in the order above what voltages do you have?
Always post any measurments from the bad and good amp for a comparison.

Forget the Zeners and crowbar for now we know that they appear to be working. The current drawn by V13 is setting the voltage on grid of V11.

It looks like u6 is acting as a comparator to control v13 compared to v11 cathode voltage.

Check the supply rails across u6 / u7

What voltage do you have on pin 2 grid V13 on both amps?

Clearly post the values you get and from which amp they come from..

Also the ref voltage for the comparator is 6.9V it goes into pin 2 of u6, however you can't measure it their so if you trace it back to the zener and measure it at that point on both amps..post the value;

Its going to be helpfull to you if you print off the circuit diagram (Big) and put in the measured values from the good amp circle each value...then put in the values next to the good amp values dont circle them so you can see at an instant what is happening.

Regards
M. Gregg
 
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#65
Okay
I have the figures for the sick amp. Across the top with the schematic voltages in parenthesis. 450 volts [447] 299.2 volts [330] 288 volts [318 volts]

Pin 2 of U6-6.17 volts

"Check the supply rails across u6 / u7" By this do you mean pins 4 & 7?

I don't know about you but I'm a little hung over. Late night. I'm going to eat a few BC powders [aspirin and cafeine] and get the figures on the good amp. I shall return.

Hasta Lluego mi compadre,
Tomas
 
#66
Hey guys,
Here are the stats on the good amp: 440 volts [447] 329.4 volts [330] 319 volts [318 volts]

Pin 2 of U6-7.18 volts

I believe what you mean by voltage to the supply rails is pin 6. If that is not it let me know.

Pin 6 of U6- 7.19

Pin 6 of U7- 4.09

I will go back and edit my results on the preceding post for the sick amp when I get its stats for pin 6 of U6 and U7

Thanx
 
#67
Yes,

Check the supply rail on the Op amps..

Do you see how V13 is controlling V11..
What voltage have you got across the ref zener? on both amps.
If you swap V13 over does the supply voltage change?

Regards
M. Gregg
 
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#68
They will not let me go back and edit that post so here it is:

Sick amp:

Pin 6 of U6-8.04

Pin 6 of U7-4.09

I think this is a good way to start. It started out as a question about zeners because I was trying to solve the discrepancies that you are seeing and turned into a full blown discussion about the amp. With these stats It will be easier for you to analyze it. Thanks again.

Regards,
Tom Wild
 
#69
WILD1 said:
They will not let me go back and edit that post so here it is:

Sick amp:

Pin 6 of U6-8.04

Pin 6 of U7-4.09

I think this is a good way to start. It started out as a question about zeners because I was trying to solve the discrepancies that you are seeing and turned into a full blown discussion about the amp. With these stats It will be easier for you to analyze it. Thanks again.

Regards,
Tom Wild
Click to expand...

The outputs of the OP amps will vary with the supply fed into pin 3 so they may not be the same.

We don't know if U6 is controlling .. something worth a try is to swap V11 over and see if the voltages between the amps change..or stay the same.. I am thinking gain..The ref should overcome this but its still worth a try..

Regards
M. Gregg
 
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#70
Another test,

You could connect to the op of U6 with a volt meter when the amp is cold. at power up the OP should change as the tubes warm up.
Compare this between the two amps.
measure Input Pin 3 U6 on the two amps post the values..

Regards
M. Gregg
 
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#71
No I don't really understand that but I do see how one side is connected to the control grid of V13 and the other to the grid of V12. Are you saying that it is regulating the voltage to these grids?

Across zeners connected to cathode of V13

U6 side:

Sick amp- 12.37 volts

Good amp- 11.49 volts

U7 side:

Sick amp- 12.17 volts

Good amp- 11.69 volts
 
#72
OK,

Here is what is happening..The current drawn through R123 creates a voltage drop. if the current varies the VD will vary..

So U6 is controlling V13 this in turn alters the volt drop across R123
Some of the voltage from the cathode of V11 is fed back to u6 this is compared to Ref voltage at pin3 U6, the OP from U6 will vary dependant on what is seen at Pin3 U6, and will alter the current drawn by V13 until the voltage seen at Pin 3 U6 reaches a value this is closed loop control.

Regards
M. Gregg
 
#76
Okay Greg with the sick amp cooled down I connected to pin 6 of U6 [output] and turned the amp on. The voltage shot up to around 15 volts then collapsed to around 1 or 2 volts then settled down to the 8.04 volt reading. I really wasn't ready for what it did so I think I will check the good amp and then come back and check the sick amp again for some little more precise readings.
 
#77
WILD1 said:
So your saying don't check them just replace them?
Click to expand...


If you lack good diagnostic skills yes I would just replace them, and that IME will usually fix the problem.. Usually if pins 2 and 3 do not match each other to within a couple of mV the op-amp is bad, checking pin 6 if bad it will usually be stuck at one supply rail or the other.. I've seen some collateral damage, but in all cases those op-amps were bad. Also check the servo op-amp in the front end once the rest of it is working.

Most of the zener strings in the amplifier are for protection in the event of some component failures, or during warm up, the op-amps servo the output voltage from their specific references, and are always in control of the loop if everything is working as it should..
 
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