Hello All,
Can anyone tell me the best way to measure plate and screen dissipation using an ultralinear output transformer when tubes are wired directly to the transformer.When running the amp,the plate voltage is much less than the screen voltage.Is this a problem?I always thought the screen voltage should be at or below plate voltage.
Much Thanks,
Tom
Can anyone tell me the best way to measure plate and screen dissipation using an ultralinear output transformer when tubes are wired directly to the transformer.When running the amp,the plate voltage is much less than the screen voltage.Is this a problem?I always thought the screen voltage should be at or below plate voltage.
Much Thanks,
Tom
we are concerned with idle conditions, a check on the cathodes for current is usually all it takes, and at idle we do not want the tube dissipating more than what the datasheets say, 80% of plate dissipation is typical, lesser for longer tube life...
connect a 100 Ohm resistor between the screen and UL tap, and a DMM allows you to measure the screen current, Is.
You will get 100mV/mA of current.
Screen current x screen voltage = screen Watts.
Is it below the maximum rating for the tube?
If the cathode has a self bias resistor Rc, measure the cathode voltage, Vc.
Vc/Rc = cathode current, Ic.
Ic - Is = Ip, the plate current.
Measure the plate voltage, Vp.
Ip x Vp = plate watts.
Is this within the maximum plate dissipation rating of the tube?
If there is no self bias resistor, then connect a 10 Ohm resistor between the plate and the plate tap. Measure the voltage across the 10 Ohm resistor with a DMM.
You will get 100mV/10mA of current.
You will get 100mV/mA of current.
Screen current x screen voltage = screen Watts.
Is it below the maximum rating for the tube?
If the cathode has a self bias resistor Rc, measure the cathode voltage, Vc.
Vc/Rc = cathode current, Ic.
Ic - Is = Ip, the plate current.
Measure the plate voltage, Vp.
Ip x Vp = plate watts.
Is this within the maximum plate dissipation rating of the tube?
If there is no self bias resistor, then connect a 10 Ohm resistor between the plate and the plate tap. Measure the voltage across the 10 Ohm resistor with a DMM.
You will get 100mV/10mA of current.
that is no easy matter for a newbie, safety is prime concern, but for those used to doing tubes, go ahead...
TonyTecson,
Thanks for the safety reminder to all of us, Newbies and Old Hands.
I wish all the readers on this forum would read the Danger High Voltage warning at the Home Page.
Unfortunately, there are less than 4000 reads of that message.
Also, It never ceases to amaze me how many schematics on this site do not even include
bleeder resistors.
And so often the ones that do include a bleeder, are too high of a resistance to discharge the caps before the amp is turned off, and the screws come out of the bottom plate, and the hands go in for a shocker!
Speed kills.
Thanks for the safety reminder to all of us, Newbies and Old Hands.
I wish all the readers on this forum would read the Danger High Voltage warning at the Home Page.
Unfortunately, there are less than 4000 reads of that message.
Also, It never ceases to amaze me how many schematics on this site do not even include
bleeder resistors.
And so often the ones that do include a bleeder, are too high of a resistance to discharge the caps before the amp is turned off, and the screws come out of the bottom plate, and the hands go in for a shocker!
Speed kills.
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i use bleeder resistor as a matter of practice....
schematics do not indicate them maybe because it is assumed that the user will use bleeders, an unsafe assumption i know...
schematics do not indicate them maybe because it is assumed that the user will use bleeders, an unsafe assumption i know...
TonyTecson,
I always enjoyed my time in the Philippines, but I forgot about the 220V power there.
I always enjoyed my time in the Philippines, but I forgot about the 220V power there.
in some parts like in the vicinity of the former Clark Air Force base, there are still 110 volt service still existing...
I lived on and off Clark Air Base.
There were so many Airman and Civilians there, it made sense to
have 110V at their residences.
It was such a beautiful place before Mt. Pinatubo blew up.
There were so many Airman and Civilians there, it made sense to
have 110V at their residences.
It was such a beautiful place before Mt. Pinatubo blew up.
You can also measure the resistance of the transformer windings (amp switched off), and then with the amp switched on you can measure the voltage drop across each part of the winding, and figure the current that way. (You'll need to subtract the anode current portion from the total, to find the screen current)
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