Well ok, true that's hot switching... but rectifiers still surely find the hardest service of anything, <40uF or whatever limit or not. And they work fine.
So getting to my point, if we agree that especially class AB amps have no chance of cathode stripping, why are people worried about it to such lengths? I know I've seen threads here, vaguely recall seeing you in them somewhere, recommending soft starts...
Nope, my amps all discharge that completely all due to the tubes. Even that 5x12AX7 + 6SN7 active preamp I made, which uses a whopping 220uF on it (yep... I just said, to heck with winding a choke, I'll just weigh it down after a resistor). Although that has a few dividers, three being insignificant but the fourth is two 22ks in series (for heater bias... it's a very DC coupled circuit) which ought to help it out a bit.
Just because tubes are used at >200V doesn't mean they don't conduct at 10V. Hept'AU7, which features 60uF around the CLC filter still produces sound 20 seconds after killing power. It's really quiet and distorted but still conducting.
And the final point... Pentodes have a CCS plate curve (like transistors). Hence Zo is almost exclusively the load resistor, and slew rate is determined by the supply current. A 6AU6 at a common level of say 1 or 2mA, especially driving a triode, ought to be very slow indeed...
Tim
So getting to my point, if we agree that especially class AB amps have no chance of cathode stripping, why are people worried about it to such lengths? I know I've seen threads here, vaguely recall seeing you in them somewhere, recommending soft starts...
Nope, my amps all discharge that completely all due to the tubes. Even that 5x12AX7 + 6SN7 active preamp I made, which uses a whopping 220uF on it (yep... I just said, to heck with winding a choke, I'll just weigh it down after a resistor). Although that has a few dividers, three being insignificant but the fourth is two 22ks in series (for heater bias... it's a very DC coupled circuit) which ought to help it out a bit.
Just because tubes are used at >200V doesn't mean they don't conduct at 10V. Hept'AU7, which features 60uF around the CLC filter still produces sound 20 seconds after killing power. It's really quiet and distorted but still conducting.
And the final point... Pentodes have a CCS plate curve (like transistors). Hence Zo is almost exclusively the load resistor, and slew rate is determined by the supply current. A 6AU6 at a common level of say 1 or 2mA, especially driving a triode, ought to be very slow indeed...
Tim
Hi,
Yes...Never said anything to the contrary.
Because people read all kinds of wrong information as far as I can tell.
If I'd recommended a soft start it would be in a different context but nothing to do with cathode stripping...
See, I told you before you had the wrong idea in the first place.
If the filaments are biased they're probably not floating either but referenced to ground, so I assume that's how the caps are drained.
Provided the cathode is heated, yes they will of course conduct.
The load resistor being which one exactly? g'?
Not sure I follow you on this...
Cheers,
Yes...Never said anything to the contrary.
Because people read all kinds of wrong information as far as I can tell.
If I'd recommended a soft start it would be in a different context but nothing to do with cathode stripping...
See, I told you before you had the wrong idea in the first place.
If the filaments are biased they're probably not floating either but referenced to ground, so I assume that's how the caps are drained.
Provided the cathode is heated, yes they will of course conduct.
The load resistor being which one exactly? g'?
Not sure I follow you on this...
Cheers,
fdegrove said:
Ok then, hoped so.
No, referenced to half B+. But filaments are beside the point. (Interestingly enough, they floated around there without the bias. Says something for the H-K diode!)
So why do you doubt they are discharging it?
The load resistor being which one exactly? g'?
Not sure I follow you on this...
Cheers,
All resistance in this case. If the tube had a (perfect) CCS supply, Zo would be Rp alone, some 10s of megohms depending. Rl and Rg will shunt that a bit...
Tim
Hi,
Because I very much doubt the cathode will remain hot once you've switched off the amp....
That's how those caps keep their charge for a month or so in the amp I was referring to....
We could have discussed this for ages....
O.K....That's what I thought you'd mean anyway.
Oh...just to make sure you don't have the wrong idea again: I have nothing against penthodes per se...
Must be that other person...again...
Because I very much doubt the cathode will remain hot once you've switched off the amp....
That's how those caps keep their charge for a month or so in the amp I was referring to....
We could have discussed this for ages....
O.K....That's what I thought you'd mean anyway.
Oh...just to make sure you don't have the wrong idea again: I have nothing against penthodes per se...
Must be that other person...again...
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