I have problem with red plating on my JCM800 50w clone,is the same on several pairs that i tried; EL34 450V plates-435 Screens,bias -30V, on pins 1 and 8 cant go over 5ma or 10mV without red plate on every tube that i tried in,left or right position. screen resistors 1K,Grid stop resistors 4,7K,Grid leak resistors 220K,bias is from separate winding with bridge rectifier.
I changed all filter caps,rewired all grounds and new output transformer,lifted coupling caps from phase inverter and connected sides from inverter to ground an no change, i see red plating even on stand by(don't know if is that normal),is the problem in bias supply?
Strange red plating tubes on new build
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Strange red plating tubes on new build
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Last edited by Guitarxtc on Sun Oct 31, 2021 8:48 pm, edited 2 times in total.
Re: Strange red plating tubes on new build
That's not normal. In fact, it's impossible in a properly wired amp.i see red plating even on stand by(don't know if is that normal)
Your bias supply is dangerous. Without a resistor on the bottom side of your bias pot, it's possible to adjust the bias voltage to zero! Very bad for tubes.
Re: Strange red plating tubes on new build
On a stock 2204, the standby switch interrupts the high voltage supply to the diodes. If you wired it that way, it can't possibly redplate on standby. How are you measuring plate current? Unless it's oscillating, I can't see how it could idle at 10mA and redplate.
Re: Strange red plating tubes on new build
Your diodes are wrong. That would short out your winding. Maybe you didn't draw it correctly?
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Stevem
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Re: Strange red plating tubes on new build
If you indeed have -35 on pin 5 of both outputs and indeed you are reading only 10 ma thru a 1 ohm resistor with a meter set for dc bolts across pins 1-8 and ground, then you can’t possibly be having tubes red plate with no signal going thru the amp.
Can you take a picture of them in the dark red plating a bit and post it up please?
You do However need a bleed resistor to ground off of the bias pot, like maybe 10k to 15k.
Can you take a picture of them in the dark red plating a bit and post it up please?
You do However need a bleed resistor to ground off of the bias pot, like maybe 10k to 15k.
Last edited by Stevem on Sun Oct 31, 2021 8:05 pm, edited 1 time in total.
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Strange red plating tubes on new build
I wired bias that is on with only power switch, actually is 5.17mA on through 1ohm resistor with -30V bias on pin 5. you can see in photo redplating on standby?
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Re: Strange red plating tubes on new build
sorry i did't draw correctly
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sluckey
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Re: Strange red plating tubes on new build
I think that's just illumination and reflections from the heaters.you can see in photo redplating on standby?
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Stevem
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Re: Strange red plating tubes on new build
And yes your diodes are wired wrong !
The point that you now have going to ground should be the negative output that you want, and what you now have as the output should go to ground.
Also you filters have way too high of a voltage rating, they will not last all that long and they will not provide the greatest filtering while they are still good!
I would not use more then 200 volt rated filters.
This is how the bridge should be used, with positive going to ground.
The point that you now have going to ground should be the negative output that you want, and what you now have as the output should go to ground.
Also you filters have way too high of a voltage rating, they will not last all that long and they will not provide the greatest filtering while they are still good!
I would not use more then 200 volt rated filters.
This is how the bridge should be used, with positive going to ground.
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Last edited by Stevem on Sun Oct 31, 2021 8:33 pm, edited 1 time in total.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Strange red plating tubes on new build
Left side on the photo is -103V after rectification and is negative on pin 5,previous i had 160V rated filters and is the same,i rewired many times to see if will improveStevem wrote: ↑Sun Oct 31, 2021 8:23 pm And yes your diodes are wired wrong !
The point that you now have going to ground should be the negative output that you want, and what you now have as the output should go to ground.
Also you filters have way too high of a voltage rating, they will not last all that long and they will not provide the greatest filtering while they are still good!
I would not use more then 200 volt rated filters.
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Stevem
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Re: Strange red plating tubes on new build
Pull out your outputs, set your meter for ac volts and read what you have on pin 5 of either tube, do you have AC volts showing up there?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Strange red plating tubes on new build
You have you meter set to current instead of voltage. Measuring across a 1 ohm cathode resistor you want millivolts, not milliamps. Let's see what the tubes are really pulling.
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Stevem
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Re: Strange red plating tubes on new build
Let me say this one more time for you, if you have a 1 ohm current check resistor going to ground off of pins 1-8 then your meter needs to be set for DC VOLTS to read the idle current, NOT like what’s in your posted picture with it set for ma!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Strange red plating tubes on new build
my mistake,sorry..
is about 10mV with -30V bias,i tried another EL34 pair and i got same readings
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