Took the rocket to jam nite for a real world test and found my pair of celestions are blown . hooked up to an Ampeg 1 x 15" SVT cab. - Wow - talk about thunderous BASS - yikes . After a little tweaking sound was excellent , but way too loud , this amp seems as loud or louder than my Red Knob twin (Evil Twin) . Played for about an hour or so and found the PT getting quite warm .
I wonder if the VOX / Hammond replacement is up to snuff
primary 120vac
secondary 275/275 @ 200mA
6.3 vac @ 6 A
5 vac @ 3 A
If I pull 2 of the 84`s do I have to change anything besides output impedance????
If this is a cathode biased power amp, you *cant* pull two tubes... your bias will be WAY off and you may cook it. Same holds true for AC30's - which the Rocket is based on.
All four tubes are parallel with the single 50ohm cathode resistor to ground . Why would 2 draw more current , all cathodes see the same 50/220uF reference to ground ?? Total current in this circuit should drop in half? no??
Nope - 4 tubes sharing a 50 ohm cathode resistor is like each tube having a 200 ohm resistor. 2 tubes on a shared 50 ohm is like each tube having a 100 ohm resistor. Things will ensue - they will be bad things...
Macshaft wrote:All four tubes are parallel with the single 50ohm cathode resistor to ground . Why would 2 draw more current , all cathodes see the same 50/220uF reference to ground ?? Total current in this circuit should drop in half? no??
What's important is the voltage drop across the cathode resistor. With 4 tubes you have 4 times as much current flowing through the cathode resistor compared to one tube, so the cathode voltage will be 4 times greater. Hence, if you want the same cathode bias voltage, you use a resistor 4 times smaller (i.e., 200 ohms -> 50 ohms).
If you want to use 2 tubes, don't just pull 2 out. You have to bump up the cathode resistor. I would use 130R instead of 100R, though.
