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Old 7th July 2004, 09:35 PM   #1
alk is offline alk  Europe
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Default amp in trouble

Hi tube freaks,

i have been tweaking in my amp= now it doesn't work.
Lat time i blew a condenser and i said to myself:you won't be touching it again but ....
What i did was change the power supply and resolder a few resistors. No power now...no wonder only 8v in the anode. Before the last resistor(anode one) i read 235V, once it passes through the 100K anode resistor multimeter(a new one) says 8V. Surprised it still sounds( low volume) but as bad as my PC soundcard.


Possibly is the new power trafo which was handwound...and hasn't got the power...but why it waits until the last resistor to drop?
Could it be something else? The last condenser? A short in the valve socket? Amp has only one valve. Monoblock.
How much juice a PCL86 se monoblock needs?

p.s. some people may be tempted to advice me against high voltage dangers seeing that i'm a newbie...i appreciate it but don't waste your time...i don't respect 230V anymore, i have taken several shocks and it's ok... i write faster now (this is a joke). Serious now, i would never attempt to build a 400V one.
But please tell what voltage really kills?
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Old 7th July 2004, 11:12 PM   #2
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Hi,

Quote:
once it passes through the 100K anode resistor multimeter(a new one) says 8V.
Have you measured that resistor already?

Quote:
But please tell what voltage really kills?
As far as I'm concerned: ANY voltage.

Cheers,

SAFETY
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Old 7th July 2004, 11:34 PM   #3
alk is offline alk  Europe
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Thanks for the reply fdgrove...now i know more, it's not the power trafo. I've plugged it to line and i guess if it can drive a microwave certainly could drive my amp.
The resistor is Kiwame and it reads exactly 100K Frank.
I suspect of the valve socket so i'm going to check.
I will read the safety measures.
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Old 8th July 2004, 12:56 AM   #4
alk is offline alk  Europe
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The valve socket seems to be ok...i don't get it. Forgot to say earlier that when connected to my house 230V line the plate read 24V. An improvement!!!! From line to anode there's the ss bridge, a 47 uf cap followed by a 330 Ohm resistor followed by a 100 uf cap followed by a 47k resistor followed by a 47uf cap and a final 100K resistor to plate. The voltage goes right until the final resistor but it reads ok so....

Now i'm lost and don't know what to check. At my wit's end.
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Old 8th July 2004, 06:53 AM   #5
dhaen is offline dhaen  Europe
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Please post a schematic, and tell us what voltages you are getting
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Old 8th July 2004, 06:54 PM   #6
alk is offline alk  Europe
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schematic? i have post it mant times...bored

the clue is here: as the filaments heat up the voltage drops slowly....Have 2 power suplies now and the plate reachs to 280V which is the correct value but when i switch on the filaments supply the voltage drops slowly to 140V. Yes before the drop was to 8V but i did rewire everything and found a mistake....had a 220 ohms cathode resistor in the triode input instead of the 330 Ohms which is the value that appears in the schema. That may be what has raised the voltage...so if put a bigger resistance in the cathode will i get more volts? The amp was working well with the original schematic. The 330 ohm resistor was there before and the amp worked at full potential now it doesn't.
Everything is ok so i must assume my OT went wrong. I have tried different valves and still the same problem.
What can it be?
I have checked all the resistors,they're ok. Could it be a faulty condenser?
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Old 8th July 2004, 07:15 PM   #7
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Hi,

Quote:
Everything is ok so i must assume my OT went wrong.
Just disconnect it and measure the voltages again.

Cheers,
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Old 8th July 2004, 07:28 PM   #8
dhaen is offline dhaen  Europe
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Quote:
schematic? i have post it mant times...bored
Fine
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Old 8th July 2004, 07:33 PM   #9
karma is offline karma  Canada
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heh i had that problem building my preamp the b+ would drop as it warmed up. was driving me nut's. i had one bad rectifier and needed a new cap on the power supply problem solved


not saying that is it. thats what it was for me


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Old 8th July 2004, 08:33 PM   #10
alk is offline alk  Europe
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Good Karma!!!
I have the feeling the ss bridge may be the cause....going to replace it now. John you are right...i was a bit stupid but i had the feeling the schema wouldn't help here and i have post it several times so i assumed ppl were already sick of seeing it....
Karma how did you find the leaky cap? Did you change one by one? Well i am going to work a little and stop the questions.
Thanks to all...and dhaen sorry for being rude...must have been solder fumes...
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