Preparing to install new pair of 4cx300y tubes (rated 400w, packed in cans, 1 army green/ 1 silver color). This will be my second tube swap with tetrode amp. When I first got it working I used an old pair of 300Y's to get it going before I installed new 300A's. Past month or so I've got the old Y tubes back in to make the changes needed to run the Y's.
I've got about a dozen 4cx300 tubes. Most are old/used 300y's with 1 pair new Y's and 4 new A's. Over the past year I've learned what to expect concerning plate & screen current from the new 300A tubes (300w) so I should be able to discern the difference btwn them and the Y's (400w).
The last few months I Reset Screen standing current/trip, Bias/Screen Voltage and I'm only starting to recognize how the old Y tubes were deficient. Basically, low plate current. My only other tube experience is 811 & 572b's. These 4cx tubes are rather tough compared to the 811/572b's. I went through a new quartet of Penta 572b and several 811a's with half the rookie mistakes I've already made on my 4cx300's.
That's normal right? When tubes get old the plate current drops and/or datasheet zsac becomes unattainable despite correct voltage and current availability? I guess I should understand what a tube tester actually measures.
Anyway, the datasheet Filament currents for these tubes are freaking interesting: The 4cx250b is 2.6A; The 4cx300A is 2.9A and the 4cx300Y is 3.5A. Yet all 3 tubes have the same body/shell & Socket. There must be differences in operating Temps too.
My Heater Xfrmr is 10A so I'm good there. If my tank roller coil holds together, I'll have something to report. Soon.
I've got about a dozen 4cx300 tubes. Most are old/used 300y's with 1 pair new Y's and 4 new A's. Over the past year I've learned what to expect concerning plate & screen current from the new 300A tubes (300w) so I should be able to discern the difference btwn them and the Y's (400w).
The last few months I Reset Screen standing current/trip, Bias/Screen Voltage and I'm only starting to recognize how the old Y tubes were deficient. Basically, low plate current. My only other tube experience is 811 & 572b's. These 4cx tubes are rather tough compared to the 811/572b's. I went through a new quartet of Penta 572b and several 811a's with half the rookie mistakes I've already made on my 4cx300's.
That's normal right? When tubes get old the plate current drops and/or datasheet zsac becomes unattainable despite correct voltage and current availability? I guess I should understand what a tube tester actually measures.
Anyway, the datasheet Filament currents for these tubes are freaking interesting: The 4cx250b is 2.6A; The 4cx300A is 2.9A and the 4cx300Y is 3.5A. Yet all 3 tubes have the same body/shell & Socket. There must be differences in operating Temps too.
My Heater Xfrmr is 10A so I'm good there. If my tank roller coil holds together, I'll have something to report. Soon.
