I've always thought that if Lynn Olson's Karna had the output stage removed and an output transformer put in pace of the last interstage, it would make a dandy little PP 45 amp.
Is there any reason why not? Am I missing why VR tubes as shunt regulators (and maybe a CCS, as in the Karna) on the output of a low-power PP amp shouldn't be used?
There don't seem to be examples in schematics, which maybe should tell me something. Not effective? Cost? Causes other problems?
Thanks. As always, I'm much indebted to the collective knowledge here.
Is there any reason why not? Am I missing why VR tubes as shunt regulators (and maybe a CCS, as in the Karna) on the output of a low-power PP amp shouldn't be used?
There don't seem to be examples in schematics, which maybe should tell me something. Not effective? Cost? Causes other problems?
Thanks. As always, I'm much indebted to the collective knowledge here.
Plenty of designs use regulated B+. The limited current handling capability of gas discharge regulator tubes prevents their direct use with power triodes, even the #45.
Even as a shunt regulator?
The gas tubes seem to work fine as shunt regs for 45's drawing 56mA (pair) in the driver stage of the Karna
sorry if I'm being obtuse... but it seems that VR tubes would work as shunt regs in lowish current applications, say 50-75 mA draw, albeit over a narrow range of supply voltage for the gas tubes to strike
The gas tubes seem to work fine as shunt regs for 45's drawing 56mA (pair) in the driver stage of the Karna
sorry if I'm being obtuse... but it seems that VR tubes would work as shunt regs in lowish current applications, say 50-75 mA draw, albeit over a narrow range of supply voltage for the gas tubes to strike
Follow the link I provided. To function correctly, only a small current range is allowed for gas discharge tubes. Lynn Olson seems to have solved things, in the #45 case, via a CCS.
PP 45's when biased( and loaded ) Class A are well within what a gas tube can regulate. The dropping R to them will be small, or B+ will need to be substantially higher, and that puppy will get *HOT*.
Check out the SE operating points, idle current, and max current...that difference is HD2, and there will be nearly none of that in PP.
cheers,
Douglas
Having 30V of compliance with a CCS loading cold cathode regulator tubes works just fine. The datasheets even allow for 100mA operation during startup, provided the tubes get some time to run at reduced current after the rest of the circuit is up and running.
There are some ways one could get around this as well. If you had a little NPN transistor setup under the output stage such that when the output tubes started to conduct, the NPN would be biased on, then stack the VR tubes on top of the output of the NPN so that it can only conduct current when the output tubes are plugged in, warmed up, and operating properly.
There are some ways one could get around this as well. If you had a little NPN transistor setup under the output stage such that when the output tubes started to conduct, the NPN would be biased on, then stack the VR tubes on top of the output of the NPN so that it can only conduct current when the output tubes are plugged in, warmed up, and operating properly.
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