• 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.

Zeners and voltage regulation

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#41
No problem. Other than I don't know where the hell it is or for that matter what it is nor how to check the voltage to it or what the voltage should be. I am definitely going to need a bottle of Tequila before the night is over. Any help would be greatly appreciated. Not with the tequila but with the questions I have about this Q2. I have reached the limits of my expertise.

Dazed and confused,
Tom Wild [WILD1]
 
#43
WILD1 said:
No problem. Other than I don't know where the hell it is or for that matter what it is nor how to check the voltage to it or what the voltage should be. I am definitely going to need a bottle of Tequila before the night is over. Any help would be greatly appreciated. Not with the tequila but with the questions I have about this Q2. I have reached the limits of my expertise.

Dazed and confused,
Tom Wild [WILD1]
Click to expand...

Lets try an easy one first look at R144 see what voltage you have should be -253 its connected to the base of Q2 follow the connection down to bottom of the drawing..

Q2 is under the string of zeners..2n4403
 
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#45
Thanks Greg,
I will find it but I think it is under the lip of the chassis where the zeners are and to get to them I had to basically stand the amp up with face down and go in from the bottom. Not an easy task. Reminds me of working on compact cars, Give me a one ton truck or a John Deere. I will Post when I find it. Kevin do you know the M100s well enough to give me some clues?

Thanks everyone,
WILD1
 
#47
Just for reference,


SCR is Q4. Gotta go again it was just a thought...


Regards
M. Gregg
 

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#48
Okay guys and gals
I found them. One is tucked under the chassis up by the Transformer and one is tucked under the chassis way back by where the 120V line comes in. With the caps there I didn't even know any thing was back there I finally found The Q4 or SCR up by the Transformer and then traced two small wires back to Q2 2n4403. I need a break. Thanks Evette for your input and for that matter thanks to everyone. I will post when I get back.
 
#49
Can't see the schematic but one use of zeners in a tube amp is to temporarily limit voltages, either on start-up or under fault conditions.

I even did this on one of my Sansui 220 receivers, so when the HT appears the little tubes don't see too much voltage before the tubes warm up and drag down their anode voltages..
 
#52
It means that the SCR is not conducting, which is good - crowbar not activated.

I think you stated that grid voltage was 8.4V and cathode was 8V on the sick amp. If so, you have positve bias which would mean that the tube should draw a LOT of current. However it does not really make sense since this ought to produce even lower plate voltage than the 261V.

But please remeasure these values.

/Olof
 
#56
M Gregg said:
Ok so you have experience ...LOL
I'll step back which one normaly goes?
Why do it the hard way..LOL 😀

<snip>
Click to expand...
I'd start with U6. (Wise to replace U7 since it shares supply rails) In my experience the op-amps blow up frequently and almost nothing else. I used to repair a lot these amps back in the 1990s and the failures were so frequent that I finally refused to repair them anymore.

Tube rolling in the output stage with inferior tubes which fail catastrophically (not the recommended/screened ARC output tubes) will generally result in a lot of destruction due to amp wide power supply transients.

It is very difficult to get the parts out because of the heavy copper and thick pcb. You might consider socketing them with machine sockets. The TL-071 is stable enough for the additional lead inductance to not cause a problem.
 
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