I have this amp:
http://www.schematicheaven.com/gibsonamps/ga19rvt.pdf
I really love the tone this cheap little amp gives.
I dropped the 5y3 and need to get another. I have a NOS RCA 5r4 and as I understand its the next step up from the 5y3. Thats just from reading on KCA's rectifier swap chart.
I popped the 5r4 in and I like the sound even better than the 5y3 and think I could easily gig the amop with that tube cause it has more headroom.
So its the usual question: will it hurt the amp?
I dont know how to check plate voltage but have a multimeter. I dont know what it takes to do it.
The amp has new atoms and new tubes. Im just installed a pair of new Tung Sol 6v6's and also have a paid or EH's I could use.
So Im also asking what specifically would it harm if the amp can't take that rectifier? If its just that the power tubes wont last as long then I dont care. If the tranny will melt then that would be bad unless I could get a bigger tranny and run a gz34.
I appreciate your thoughts . In the meantime, Im going to search about checking plate voltages but if you could point me to the right direction I'd be grateful!
Thanks
Gibson falcon GA-19 rectifier/plate voltage question?
Moderators: pompeiisneaks, Colossal
Re: Gibson falcon GA-19 rectifier/plate voltage question?
The 5Y3 tube drops around 60 volts while the 5R4 drops around 67 volts.
So no big difference there.
They both draw 2 amps current.
The 5R4 looks to be a heavier duty rectifier.
Your amp was built when house current was 110 volts.
Most places are 120v nowadays.
So all the voltages will be higher as a result. Too high?
That remains to be seen.
But I think you are safe running the 5R4 rectifier tube.
Your amp is cathode biased so it is what they call self biasing.
But, since the house current is now 10 volts higher it may be biased higher too.
Checking the bias current in a cathode biased amplifier is easy, just measure the voltage across the cathode resistor and divide by the resistance value to obtain the cathode current. Note that if the output tubes share a common cathode resistor, you must divide the current reading by the number of tubes sharing the resistor. Note also that a common cathode resistor does not allow you to determine the individual currents of each tube, so if one tube is drawing more current than the other, you would not be able to determine which is causing the mismatch, and, in fact, you would not be able to tell there was a mismatch at all. You can add individual 1 ohm resistors from the cathode of each tube to the common bias resistor, but you must then measure across the 1 ohm resistors, not from the cathodes to ground, to determine the voltage drop, and thus the cathode current. You can also use individual cathode bias resistors on each tube. The value of the resistor will be double that of the common resistor if two tubes are used, or four times that of the common resistor if four tubes are used. Each resistor would also have to be bypassed with its own electrolytic bypass cap.
http://www.aikenamps.com/
So no big difference there.
They both draw 2 amps current.
The 5R4 looks to be a heavier duty rectifier.
Your amp was built when house current was 110 volts.
Most places are 120v nowadays.
So all the voltages will be higher as a result. Too high?
That remains to be seen.
But I think you are safe running the 5R4 rectifier tube.
Your amp is cathode biased so it is what they call self biasing.
But, since the house current is now 10 volts higher it may be biased higher too.
Checking the bias current in a cathode biased amplifier is easy, just measure the voltage across the cathode resistor and divide by the resistance value to obtain the cathode current. Note that if the output tubes share a common cathode resistor, you must divide the current reading by the number of tubes sharing the resistor. Note also that a common cathode resistor does not allow you to determine the individual currents of each tube, so if one tube is drawing more current than the other, you would not be able to determine which is causing the mismatch, and, in fact, you would not be able to tell there was a mismatch at all. You can add individual 1 ohm resistors from the cathode of each tube to the common bias resistor, but you must then measure across the 1 ohm resistors, not from the cathodes to ground, to determine the voltage drop, and thus the cathode current. You can also use individual cathode bias resistors on each tube. The value of the resistor will be double that of the common resistor if two tubes are used, or four times that of the common resistor if four tubes are used. Each resistor would also have to be bypassed with its own electrolytic bypass cap.
http://www.aikenamps.com/
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Gibson falcon GA-19 rectifier/plate voltage question?
You should be able to use 5Y3, 5R4, 5V4 OR 5AR4 with no problems. All need the same filament current. You'll likely see a little more B+ voltage with the 5R4. You'll definitely see more B+ with the 5V4 and the 5AR4 (especially the 5AR4) as these are indirectly heated.
To measure plate voltage, just set your DMM for VDC and put the black lead to ground and the red lead to an output tube plate.
To measure plate voltage, just set your DMM for VDC and put the black lead to ground and the red lead to an output tube plate.