I finally found a better power supply transformer match for my endlessly fiddly little DIY linestage/preamp project. Only 5V too high in this case.
But maybe it isn't really too high, taking into account the load presented by a 12AU7 after it warms up and starts to conduct? It sure would be nice if this is gonna be OK now that I have the hum issues worked out.
Specs say max. 300V on the plate.
Downstream of the 100K feed resistors on plate pins 1 & 6, at power-on with cold filaments, for a short time I have 305V.
Quickly drops to around 90V as filaments warm up.
Do the tube specs refer to plate voltage after idle conduction starts? Thus the second uncertainty: if that's supposed to be the unloaded value post-dropping-resistor, is 5V over still acceptable for a few seconds before filament warmup?
Once again, thanks in advance for all of y'all's lovely input on this. 🙂
But maybe it isn't really too high, taking into account the load presented by a 12AU7 after it warms up and starts to conduct? It sure would be nice if this is gonna be OK now that I have the hum issues worked out.
Specs say max. 300V on the plate.
Downstream of the 100K feed resistors on plate pins 1 & 6, at power-on with cold filaments, for a short time I have 305V.
Quickly drops to around 90V as filaments warm up.
Do the tube specs refer to plate voltage after idle conduction starts? Thus the second uncertainty: if that's supposed to be the unloaded value post-dropping-resistor, is 5V over still acceptable for a few seconds before filament warmup?
Once again, thanks in advance for all of y'all's lovely input on this. 🙂
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Don't worry about it at all... Those tubes can handle 500+ volts on the plate when it's cold and warming up. It's fine.
Thanks.
I just remembered that someone else thought the mfr. specs called for a higher-value feed resistor, too.
I just remembered that someone else thought the mfr. specs called for a higher-value feed resistor, too.
Yeah, you're fine. Less than a 2% difference is a level of precision way beyond DIY audio. That would be like NASA around here
All good fortune,
Chris
All good fortune,
Chris
Most european datasheets state max. plate voltages also for the switch on period where heaters are still cold (Va0 in datasheets) and anode current is zero. For the 12AU7 (=ECC82), Philips specifies +550V.
Danke schön and gracias. Exactly what I was needing to know. Evidently not necessary to change anything.
Oh happy joy. I'm a little ashamed at not having found that information on my own, and thanks.