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In Reply to: RE: He didn't specify class A1 or A2 posted by Ralph on April 02, 2025 at 12:44:57
Ok but I have never seen a data sheet showing Class A2 operation of a 300B.
I don't think the tube was designed for that but I could be wrong.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
What you do is make sure you're not exceeding the max dissipation; actually you can design the circuit so you're well within parameters.
I thought in a tube intended of Class A2 operation the grid had to be designed to stand up to the current that is not present in Class A1?Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/03/25 04/03/25
Some tubes are rated for maximum grid dissipation, or max grid driving power, or max DC grid current. The 211 is an example. Some tube data sheets even include curves for positive grid voltage. I presume these indicate suitability for A2/AB2/B2/C2 operation.The Type 45 is explicitly rated for AB2 operation.
Some other tubes specify a max grid voltage of zero, presumably they are not suited to such operation.
Edits: 04/04/25
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Its likely that some tubes are better at it than others. But I don't know which they might be. I do know from having done it that 300bs have no problems with it at all.
If I use 5VDC for 300B Filament, should I use separate 5V for each 300B. Or I can use the same 5VDC for both 300B?
That will make it trickier to have a hum balance setup that is only one control.
I have a PP type 45 power amplifier. I don't use a hum balance, instead I was careful about the filament connection so that the hum waveform cancels in the output section. That required a minor amount of matching but since the mu of the tube is so low that was not difficult.
In my 300B SE mono block amplifiers I use critical inductance LCRCL filters and replaced my hum pots with fixed resistors.By the way the hum will only cancel in a PP design. And only if it's in phase and equal amplitude in both tubes.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 04/09/25 04/10/25
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