• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

10M45S problem

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#21
ikoflexer said:
Keep the gate resistor 1k and replace the cathode resistor that sets the current with a 2k variable resistor and very carefully adjust it in the circuit. If that doesn't make it work then switch to a gyrator (just an extra couple of resistors and one capacitor) which will probably work better anyway. 🙂 (Be careful adjusting that resistor with the high voltage present.)
Click to expand...

I'm not familiar at all with the gyrator circuit. Do you know a good resource that will help me?

I'm going to replace the left channel CCS first, as the right channel seems to work fine.

Thank you.
 
#25
ultrafi said:
Stop! Read the datasheet for the 10M45. You really need more current through the 10M45 for it to work well.
Click to expand...

My datasheet says good for 2 - 100mA. I used the data sheet to calculate the correct resistor. I could not find on my data sheet where it says it needs more current to work well. I am interested in reading more about that. Do you have a link?

Thanks.
 
#27
I disconnected the gNFB feedback loop today and voila, the CCS works fine.

I haven't had time to go any further. Since the right channel worked, and the left channel had the problem, I'm guessing that one of the output transformers had the blue & brown plate wires reversed from the factory.

I'll put it on the scope when I get a chance and verify that.

Thanks for all the help.

Scott
 
#32
scott17,

I am thinking of using the current source in the same position as yours(the driving tube is a triode not a pentode like yours), do you use a heat sink on the 10M45? I am using about 2-3 mA though this IC and about 150V across it.
 
#33
Yes, I did use a heat sink. I'm not sure that it needs one at that current, but I erred on the side of safety anyway. I just cut a chunk off of an old CPU heat sink and tapped and threaded it. You can see them in this photo.

Don't be blinded by the LED bias circuit though!

ttan98 said:
scott17,

I am thinking of using the current source in the same position as yours(the driving tube is a triode not a pentode like yours), do you use a heat sink on the 10M45? I am using about 2-3 mA though this IC and about 150V across it.
Click to expand...
 

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#37
ttan98 said:
Scott17,

Thanks for info and warning. From your cct diagram, is the 100ohm and 1kohm positions interchange, i.e. your current cct diagram is incorrect.
Click to expand...

The drawing shown at post #20 is how it is now connected. 100R for the gate stopper, and 1K for the current set. The 1K is based on the calculation from the data sheet, and in my case it is correct and gives the correct voltage drop for my required current. The diagram is correct.
 
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#38
popilin said:
Since dissipation is small, no problem to isolate the device from heatsink with insulating washers.

Believe me, the temptation to touch a heatsink, is always stronger than our memory, and on your assembly would be a little dangerous. :wave2s:
Click to expand...

Well, my memory must be better than yours then. I know not to touch it when it is on, and I can remember not to. Since I am the only one with access to it, it is perfectly safe and not dangerous at all.
 
#39
Everything works now. It was a reversed OT primary. I know I should have checked that first, but since one channel worked and the other didn't, I suppose I overlooked it at first. My mistake. Never trust the color code or drawing. Sorry to waste so many folks time speculating since it was such an easy fix. Thanks very much.

Here is the schematic.
 

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#40
scott17 said:
Everything works now. It was a reversed OT primary. I know I should have checked that first, but since one channel worked and the other didn't, I suppose I overlooked it at first. My mistake. Never trust the color code or drawing. Sorry to waste so many folks time speculating since it was such an easy fix. Thanks very much.

Here is the schematic.
Click to expand...

Don't worry, can happen, Murphy lives...😀

The important thing is that you solved the problem. 🙂
 
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